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Audio Glossary

5-way binding post A terminal often used on Subwoofers and amplifiers that can accommodate five different connection options: banana plugs, ring and spade terminals, bare wire and through-hole pins.
A/B test A form of listening test in which two sounds are compared with each other in a rapid A/B fashion. Ideally, the listeners would not know the identity of the two products being compared. See Double-Blind Listening Test
A/D Converter A device that accepts an analog signal at its input, and outputs a digital version of the signal.
A/V Audio/Video
A/V receiver Combines the following functions in one device: audio- and video-signal switcher; surround sound decoder; multichannel amplifier; preamplifier, including tone controls and other effects; and radio tuner
Absorption In acoustical absorption, sound energy is converted into heat. See: Resistive Absorbers, Diaphragmatic Absorbers, Resonant Absorbers, Absorption Coefficient, Sabine
Absorption Coefficient The proportion of incident sound that is absorbed by a surface. Usually this is expressed as a number between 0 and 1, or a percentage. In most materials, the amount af absorption changes with the angle of incidence. The specification is normally a 'random incidence' measurement.
AC see Alternating Current
AC Line Conditioner or Protector A device inserted between the wall outlet and your equipment to isolate it from voltage spikes and unwanted high frequency signals that may be picked up by the power lines. High quality audio equipment may already have some of this kind of isolation built in. See also: AC Voltage Stabilizer
AC Voltage Stabilizer A device inserted between the wall outlet and your equipment to isolate it from voltage spikes and unwanted high frequency signals that may be picked up by the power lines. High quality audio equipment may already have some of this kind of isolation built in. See also: AC Voltage Stabilizer
AC-3 The first descriptor for what is now called Dolby Digital.
Acoustic Suspension A closed box loudspeaker enclosure in which the compliance (spring) of the air inside the box is a substantial portion of the total compliance of the system, including the mechanical suspension of the woofer. See: Suspension, Compliance
Acoustical Interference When two or more sounds arriving from different directions combine at a point in space, e.g. at an ear or microphone, those components which are in step with each other (in phase) will add (constructive interference) and those that are out-of-phase will subtract, or cancel each other (destructive interference). See: In Phase, Out-of-Phase, Comb Filter.
Acoustics The physical science dealing with how sound is produced, propagated, manipulated and perceived. See also: Room Acoustics
Active Crossover An analog or digital device performing high-pass, low-pass and bandpass functions ahead of power amplifiers driving the transducers in a loudspeaker
Active Loudspeaker A loudspeaker which has a built-in power amplifier for at least one driver, usually the woofer or subwoofer. It may also have amplifiers for mid and high frequency drivers. See: Powered Tower
Active Matrix Decoder See: Matrix Encode/Decode
AES/EBU The two-channel digital audio communication process that was standardized by the Audio Engineering Society (AES) and the European Broadcasting Union (EBU).
Aftermarket The sale of components for installation after the customer has purchased the original item. For example, aftermarket car audio equipment can embellish or replace the originally supplied system
Algorithm A step-by-step procedure for solving a problem or accomplishing a task, usually by using a microprocessor or DSP (see below). In digital audio, algorithms are often used for sound processing, data compression and surround sound en-/decoding.
Alternate Channel Selectivity A measure of the ability of a radio tuner to reject information from a radio station close to the frequency of the one being listened to
Alternating Current An electric current that moves in both directions, cycling at a regular rate, as in 60 Hz home power, or at a variable rate as in an electrical music signal being supplied to a speaker. Also used to describe the accompanying alternating voltages, cycling between positive and negative
AM see Amplitude Modulation
AM Rejection A specification describing to how well a radio tuner can ignore changes in the amplitude of an FM signal, such as those caused by propagation effects and interference
Ambience In audio this refers to the reflected and reverberant sound characteristics of an acoustic space. All rooms can be acoustically 'live' or 'dead'. Large rooms can be flattering to musical performances (concert hall) or hostile (gymnasium).
Ammeter A device used to measure current flow in amperes
Amperage The magnitude of an electrical current as expressed in amperes.
Ampere Unit of measurement for the electric current flowing through a circuit. Abbreviated: amp.
Ampere-hour A measure of the quantity of electricity delivered by a battery determined by multiplying the integrated current in amperes by the duration of the current flow in hours
Ampere-hour capacity Rating for a battery describing current in amperes that can be drawn over a period of time in hours before the discharge limit is exceeded
Amplification An increase in signal level.
Amplifier A device that increases the magnitude of the voltage, current or power in an electronic system. In audio systems, preamplifiers and surround processors amplify voltages. Power amplifiers amplify both voltage and current, therefore providing more power output in order to drive loudspeakers
Amplitude The magnitude of an electrical signal (voltage, current or power), sound (sound pressure or intensity), or movement of a mechanical device such as a loudspeaker diaphragm.
Amplitude Modulation A method of radio broadcasting in which the radio carrier frequency is amplitude modulated by the audio signal. Typically limited in bandwidth, and susceptible to interference and static. However, it propagates well over long distances and around hills and buildings. Abbreviated AM.
Analog An electrical signal in which the voltage (or current) waveform has the same form as the original acoustical sound waves. See also Digital
Analog-to-digital converter See A/D converter.
Anamorphic A film or video format in which a widescreen image has been "squeezed" horizontally (either with lenses or by digital manipulation) to fit a standard 4:3 aspect ratio. Correct picture geometry is restored on playback by "unsqueezing" the image into its original aspect ratio. Anamorphic DVDs are sometimes marked "Enhanced for widescreen TVs." See: Widescreen, Aspect Ratio
Anechoic Without echoes, reflections or reverberation.
Anechoic Chamber A room without echoes or reflections that is used for precise acoustical measurements, not contaminated by normal room acoustical factors, including noise. It is the ultimate 'dead' room. See Reverberation
Anode The electrically positive terminal of a battery, or the plate of a vacuum tube
Aperture Ratio In digital display devices, this is a measure indicating the percentage of the available area that is used for active pixels. Some displays have obvious inactive 'frames' around individual pixels, leading to the description 'screen-door' effect when viewing such a display from insufficient distance
Aquaplas A water based compound high in particulates which is used to adjust the mass of, and to add damping to, a variety of loudspeaker diaphragm materials
Articulation / Articulation Index Having to do with the intelligibility of speech. This is measured using listeners who try to identify randomly presented 'nonsense' words and phrases. The Articulation Index is the percentage of correct identifications. Used mainly in large venues.
Artifact In video, the degradation of picture details when a video decoding system cannot keep up with frame-by-frame changes. Video compression systems (codecs) rely on the common reality that only portions of a picture change from frame to frame. If a lot of the picture is changing (as in panning across a crowd of people) decoders may not be able to keep up, and the result is that portions of the picture may momentarily revert to large blocks of color. Other artifacts can be seen in jagged edges, 'staircasing' of guitar strings, etc. Fortunately, most are brief.
Artificial Reverberation Synthesized reflected sounds intended to add to a recording the acoustical impression of being in a specific size and kind of room, such as a concert hall, stadium, club, etc. Inexpensive versions tend to be very artificial sounding. The best versions are hardly distinguishable from the real thing, and in fact are used in numerous concert performing spaces to improve on less-than-perfect natural acoustics. Also, the electronic reverberation added to close-miked recordings
Aspect Ratio The width-to-height ratio of a visual image. Standard NTSC television sets have an aspect ratio of 4:3 (4 units wide by 3 units high). Widescreen television sets have an aspect ratio of 16:9. Many films are produced with even wider ratios. Pictures with aspect ratios different from the display will show dark bars at the top and bottom, or at the sides. See: Widescreen, NTSC
ATRAC Acoustic Transformation Adaptive Coding. A perceptual encoding system used in the Sony MiniDisc format. See: Perceptual Coding
Attack In music, the onset of a sound or note.
Attenuation A reduction in signal or sound level
Audio Frequency Range The range of human hearing commonly accepted as 20 to 20,000 Hertz (cycles per second)
Audio Interconnect Cable A shielded wire used to link the audio signal output of one device to the input of another audio device
Audio Oscillator A test instrument that produces single frequency tones for measuring the performance of audio devices.
Audio Signal An audio frequency signal in electronic form or after conversion to sound
Audiometer A closed box loudspeaker enclosure in which the compliance (spring) of the air inside the box is a substantial portion of the total compliance of the system, including the mechanical suspension of the woofer. See: Suspension, Compliance
Audiophile Anyone interested in the reproduction of sound.
Auto Convergence An automated feature for aligning the red, green and blue guns of a CRT projector or rear-projection television. See: Convergence
Auto Turn-on A signal sensing circuit designed to turn an audio component on when it receives a music signal.
A-weighting See Frequency Weighting
Axial Modes The acoustical resonances in rooms that occur between opposing parallel surfaces: walls, or floor and ceiling. See Room Resonances
Azimuth In tape recorders, the angle made by the magnetic gap in the record/play heads and the direction of tape motion. The playback azimuth must equal the record azimuth or there will be a loss of high frequencies on playback
Background Noise In listening, it is any sound (normally unwanted) that is not part of the sound track being auditioned. In measurement, it is extraneous sound that, if too loud, can cause errors in the measured data
Baffle The board to which loudspeaker drivers are mounted in a loudspeaker enclosure
Balance Control In stereo systems, a control to adjust relative sound levels in the left and right loudspeakers. In multichannel systems there is a front-back balance adjustment. In car audio, the front-back adjustment is called a 'fader'
Balanced Connection A method of interconnecting audio components using a three-wire cable in which there are two signal wires and one ground wire, all of which may be inside a cylindrical shield that is also grounded. The two signal conductors both have the identical impedances to the common ground terminal, hence the name Balanced. Because of this such interconnections are highly immune to ground-originated noises and hum. It is widely used in professional audio systems which routinely have very long cable runs and very complex interconnections of signal and power grounds. The XLR plug is commonly used. See: Unbalanced Connection
Banana Plug and Jack A largish, pin-type, connector commonly used to connect loudspeakers to power amplifiers
Bandpass An adjective describing a system or device that operates only over a specified range of frequencies. In audio, there are bandpass filters, as in loudspeaker crossovers, and bandpass loudspeakers as in bandpass subwoofers. In all cases, frequencies outside of the pass-band range are severely attenuated
Bandpass Enclosure A form of low-frequency loudspeaker enclosure in which chambers, drivers, and internal and external ports are configured in an integrated acoustical design that behaves as an acoustical bandpass filter, exhibiting natural low-and high-pass limits to the acoustical output. See: Low-Pass Filter, High-Pass Filter.
Bandwidth The difference between the upper and lower usable frequency limits of a circuit, a device, or a communications (radio, TV or digital data transmission) channel
Barrel Distortion In video, a form of geometric distortion in which straight lines bulge or bow outward toward the edges of the screen, e.g. making a square look barrel shaped. See: Pincushion Distortion
Basket The outer frame of a loudspeaker driver that supports the magnet, the diaphragm and other moving parts.
Bass Low-frequency audio signals. Frequencies below approximately 300Hz (below 100Hz in cars)
Bass Boost/Cut An electrical filter designed to increase or decrease the amount of bass reproduced by an audio system
Bass Control A tone control allowing the user to boost or cut the low frequency portion of the audio signal.
Bass Management A function in a multichannel surround processor that combines the low bass frequencies from all of the channels (including the LFE channel) in a recording, and directs it to the appropriate loudspeakers. To do this, the customer must tell it the number, kind (small or large), and placement of loudspeakers, and whether there is a subwoofer in the system. See: LFE
Bass Reflex A low-frequency loudspeaker enclosure design in which the volume of the enclosure and the dimensions and shape of a vent, or port, form a Helmholtz resonance which is designed to integrate with the performance parameters of a woofer. Such systems are characterized by increased acoustical output at certain frequencies near the system resonance, less output at lower frequencies, and the potential for reduced distortion at high sound levels. See: Helmholtz Resonance
Beaming See Directivity
Beats The combination or difference tone heard when two closely spaced frequencies combine in the ear. It is an intermodulation effect, or distortion
Bi-Amping In loudspeakers that have the appropriate connections, bi-amping is the practice of using two power amplifiers to drive a single loudspeaker, one for the woofer and one for the mid/high frequency section. Normally, the internal passive crossovers are used so that the manufacturer's system design is left intact (assuming that the amplifiers gains are identical, and they are in phase). In large professional systems an external electronic crossover is often used, in which case it is essential to equalize the system afterwards, since the user is really designing the loudspeaker system from the ground up. See: Bi-Wiring
Binaural Literally, two ears, or listening through two ears. Also used to describe recordings made with a dummy head microphone, with microphones at each ear location, intended for playback through headphones or two loudspeaker with acoustical crosstalk cancellation so that the sound of each loudspeaker is heard primarily by only one ear. See Monaural
Binding post terminal A terminal that provides several connection options. See also 5-way binding post
Bipole A loudspeaker system with forward and backwards firing transducers connected in the same polarity (in phase). The directional pattern is almost omnidirectional at frequencies up to a few thousand Hz, beaming slightly forward and back at the highest frequencies
Bit A binary digit, the basic unit of digital data of all kinds. It has two states, off and on, high or low, zero or one. In the encoding of audio signals, each bit translates into approximately 6 dB of useable dynamic range. Thus, the 16-bit encoding of CD's permits a maximum dynamic range of 16 x 6 = 96 dB, accompanied by very low distortion and noise. Current technology permits higher bit rates, and so we are seeing even wider dynamic ranges, e.g. 24 bits, which is useful for professional audio, and more than enough for a delivery medium
Bi-Wiring In loudspeakers that have the appropriate connections, bi-wiring is the practice of using two sets of wires from a single amplifier to a loudspeaker system, one for the woofer and one for the mid/high frequency section. See: Bi-Amping
Black Level The level of brightness at the darkest part of a visual image
Blind Testing See Double-Blind Listening Test
Blooming Video distortion in CRT display devices, caused by excessive white level (contrast) settings resulting in images that have lost focus or sharpness
BNC A high quality bayonet (push and turn to lock) connector used with some high frequency video and digital signal cables
Bookshelf Speaker A small loudspeaker system, capable of fitting on a bookshelf or in a cavity in A/V furniture. However, from a sound quality perspective, shelves and cavities are the worst possible locations for such loudspeakers. They sound best when mounted on stands away from walls and other objects
Boomy Bass reproduction in which certain notes are exaggerated or prolonged by one or more resonances. See Resonance
Boundary Effects In acoustics, the interactions between loudspeakers and listeners, and the room walls, floor and ceiling. Often refers to the interactions with boundaries that are adjacent to the source or receiver
Breakup When a loudspeaker diaphragm fails to move in a pistonic fashion, and flexes, or breaks up, distorting the sound
Bridging Combining the outputs of two amplification channels to provide one more powerful channel. Note that bridging may raise the minimum load impedance that the amplifier can safely drive
Bright, brightness In video displays, the Brightness control is used to set the black level, which determines how dark the black portions of a picture are. In describing sound quality, it refers to an excess of high frequency sound. It can be caused by electronics or loudspeakers with excess output at high frequencies, or by rooms that are too reflective, or live, at high frequencies.
Broadband A term implying very wide bandwidth. In the context of data communications it implies a connection with higher data rates (wider bandwidth) than telephone modems
Bus A signal distribution system, normally employing wire, optical fiber, which enables many components to be operated from a single control unit without each being individually linked to it. Some bus systems have two-way communication.
B-weighting See Frequency Weighting
Capacitance The property of a circuit element that permits it to store charge. The number of electrons (charge) it can hold under a given electrical pressure (voltage) is called its capacitance which is measured in farads, or fractions thereof, e.g. microfarads
Capacitor Two metallic surfaces separated by an insulator creating a device that can store an electric charge. It cannot pass DC and will pass AC signals with an impedance that decreases as frequency increases. This property makes capacitors useful in filter and crossover designs.
Capture Ratio A specification describing the ability of an FM radio tuner to lock on to one station when there is another on the same frequency that is only slightly less strong
Cathode The electrically negative terminal of a battery, or the electron source of a vacuum tube.
Cathode Ray Tube See CRT.
CATV Cable television
CAV Constant Angular Velocity. A method of recording a disc (e.g. laserdisc) in which the rotational rate is kept constant from beginning to end. Each rotation can be contrived to hold the same amount of information, such as a single frame of a picture, making perfect 'pause' functions possible in an analog medium. It is wasteful of space, however, as the density of recorded data reduces with increasing distance from the center of the disc. See: CLV
Caveat Emptor From the Latin: let the buyer beware. It is a principle in commerce that, without a warranty, the buyer takes the risk
CD CD = Compact Disc. An optical disc format for storing digital signals, developed jointly by Sony and Philips.
CD-DA CD-DA = Compact Disc Digital Audio, the original PCM digital music storage format, defined by the Red Book standard
CD-R A disc in the CD format that can be recorded once. Defined by the Orange Book standard
CD-ROM A Read-Only Memory (ROM) in the CD format, used for storing computer data. Defined by the Yellow Book standard
CD-RW A disc in the CD format that can be recorded many times. It is rewritable
CEA-2006 An amplifier rating standard provided by the Cnsumer Electronics Association and adopted my many reputable makers of car-audio amplifiers. CEA-2006 attempts to provide a basis for rating amplifers using RMS output power and a specific load impedance to ensure a useful rating.
Center channel A channel driving a loudspeaker located midway between the front left and right loudspeakers. It does most of the work in movie and television audio, anchoring dialogue to the screen. In multichannel music, the featured artist can have a private channel. Must sound as good as, and as similar as possible to, the left and right loudspeakers. In automobiles it is especially important to solidly anchor the center portion of the front soundstage for both the driver and the passenger. See Channel.
C-Format See VHS-C
Channel A signal path. Stereo consists of two channels, starting from the signal source, and ending at the loudspeakers. Multichannel audio can have 5, 6 or 7 channels, plus a so-called .1 channel for low bass sound effects
Channel Separation See: Separation
Chassis The metal frame of a vehicle, or the metal base on which an electrical circuit is constructed
Chroma The color information in a video signal consisting of hue and saturation. See: Chrominance, Saturation, Hue
Chrominance The color (hue and saturation) of light, independent of luminance (brightness), or that portion of a video signal that carries this information. Designated by the symbol 'C'. See: Luminance
Circuit Breaker A device designed to protect other electronic devices by opening the circuit when the system is drawing too much power. Since it uses relay contacts, it can be reset manually or automatically. See: Fuse
Circumaural Headphones Headphones having cushions that surround the external ear, resting on the sides of the head, not on the ear itself. See: Supraaural Headphones, In-Ear Headphones
Class A An amplifier design in which both positive and negative polarities of an audio waveform pass through devices that are active (conducting current) at all times. All low-level analog amplifiers are of this type. Class A power amplifiers are relatively uncommon because they generate a lot of heat, even when no signal is being reproduced, thus requiring enormous heat sinks and many output devices if large amounts of power are needed. See: Class AB, Class B
Class AB Basically a Class B power amplifier in which the positive and negative output devices never completely shut off, leaving a residual Class A activity at low signal levels and to smooth the transition from one polarity to the other. Less efficient, and therefore hotter, than Class B, but much cooler running than Class A. The most common form of power amplification. See: Class A, Class B
Class B A power amplifier design in which positive and negative polarities of an audio waveform pass through separate output devices that conduct only when needed. It is difficult to eliminate all distortions created when the devices transition from one polarity to the other (crossover distortion), which has relegated this design to low quality audio and other applications of power amplification where efficiency and cost are of greatest importance
Class D An amplifier design in which the positive and negative output voltages are defined by a pulse-width-modulated output section where the transistors are biased to be either on or off and provide the full voltage available from the power supply directly to an output filter. The output filter turns the pulses into an analog waveform suitable for driving loudspeakers
Clipping Distortion that occurs when an amplifier is driven beyond its voltage, current or power limit. Clipping describes the "cutting off" of signal peaks when the amplifier's limit is exceeded by playing the system too loud. Clipped signals have excess high frequencies, putting tweeters at risk, and some amplifiers become unstable when overdriven, and this also can result in damage to the loudspeakers. So, small amplifiers driven too hard can be more dangerous to loudspeakers than large amplifiers driven within their design range.
Closed Captions Text captions that can be made visible on demand. Open captions are a permanent part of the video signal
CLV Constant Linear Velocity. A method of recording a disc (e.g. laserdisc) in which the rotational rate is varied from start to finish so as to maintain a constant velocity of the 'groove' being read by the playback laser. This results in a more uniform data density over the surface of the disc, from inside to outside, allowing for longer recordings. See: CAV
CMMD™ Working in collaboration with metallurgy specialists, the resourceful Infinity transducer engineers identified a special combination of materials that exhibit a remarkably useful set of mechanical properties. Infinity’s new Ceramic Metal Matrix Diaphragms are much stiffer than standard metal diaphragms, moving the natural modes significantly upwards in frequency. At the same time, CMMD™ cones have more damping than metal cones, making this an excellent cone material for all transducers: woofers, midranges and tweeters
Coaxial Cable A transmission line in which a central conductor is located within a cylindrical outer conductor, separated by insulation. Can be designed to have specific characteristic impedances at radio and TV frequencies to minimize losses. Sometimes used in the much less demanding role of interconnect cables at audio frequencies, where they function as simple shielded wires
Coaxial Loudspeakers Loudspeakers in which the tweeter is located on the central axis of the woofer, and the two are combined in a single structural unit
Codec A combination encoder and decoder for any kind of digital signals, audio or video. See: Perceptual Coding, Compression
Coherence In listening, it describes a kind of perceptual realism in sounds. In measurements, it is a measure of the correlation between the phases of two or more signals.
Coil Turns of wire used to create inductance for use in an electrical circuit, or to create a magnetic flux when current is passed through it, or to respond to a changing magnetic field. An electrical impedance of a coil increases with frequency. See also Inductance, Inductor, Voice Coil
Color Temperature A measure of the color of light. In video, the underlying basis for a picture. A low temperature would be associated with a reddish picture, while a high temperature would yield one more bluish. NTSC standards require 6500 degrees Kelvin
Coloration In listening evaluations, a perceived characteristic of a sound that was not in the original recording. Coloration modifies the timbre of voices and musical instruments, and is therefore not a good thing.
Comb Filter AUDIO: A characteristic of a frequency response curve that appears when a sound is combined with a delayed version of itself. The name comes from the orderly, repeated, bump-dip-bump-dip visual appearance, looking like a comb. Comb filtering that occurs in a simple signal path can be annoying. However, rooms are very complicated comb filters, due to the many reflected sounds, and common experience tells us that this is usually perceived as a benefit e.g. concert halls. VIDEO: a filter that separates a composite video signal into luminance (black and white) and chrominance (color) components. See: Luminance, Chrominance, Frequency Response, Acoustical Interference
Compliance The force required to move an elastically suspended object a certain distance - e.g. the 'stiffness' of a spring. The diaphragm suspensions in loudspeakers have mechanical compliance. The air inside an enclosure has acoustical compliance
Component Video A video signal consisting of three components: red/green/blue (RGB) or a Color Difference method going by one of several names: Y,U,V or Y, Pb, Pr or Y, B-Y, R-Y. The latter is the method of video storage on DVD's and the component connection is the preferred way to communicate video infomation to displays. The green, blue and red cables may be terminated in either RCA or BNC plugs. See: Chrominance, Luminance, RCA, S-Video, BNC
Composite Video A video signal in which the chrominance and luminance signals are combined, along with synchronizing signals. These tend to use cables, looking like yellow audio cables, with RCA connectors. This is the most basic form of video found on virtually all TV's, VCR's, etc. See: Chrominance, Luminance, RCA, S-Video, Component Video
Compression AUDIO: A reduction in the dynamic range of a system. This can be done deliberately, as is common in radio broadcasts, or it can be the result of overdriving something, such as a loudspeaker where, above a certain level, the device does not respond proportionally to increases in signal level (see Power Compression). ACOUSTICS: A momentary increase in pressure as a sound wave passes. See: Rarefaction, Sound Wave. DIGITAL DATA: Reducing the amount of digital data required to store audio or video. Data compression can be lossless or lossy, depending on whether the reconstruction is exact or not. Perceptual coding is used in lossy systems. See: Perceptual Coding
Compression Driver A loudspeaker driver especially designed to drive a horn. The name derives from the fact that the sound radiating from a diaphragm is forced through a phase plug to a smaller opening (i.e. compressed) at the throat, or beginning, of the horn expansion. See: Phase Plug
Cone A cone-shaped diaphragm of a loudspeaker that vibrates and radiates sound. Loosely used to describe all diaphragms, some of which have other profiles, such as domes
Constant Directivity Horn A horn design that has a relatively constant angular dispersion of sound over its useful frequency range
Convergence In front or rear projection devices using combined red, green and blue images to form the final picture, it is necessary that all three be perfectly aligned, or converged, with each other in order to maximize the sharpness and color accuracy of the picture. It may be necessary to converge the pictures at many locations all over the picture area. A special test signal is used
Critical Band In hearing perception, it is a band, or range, of frequencies over which the ears tend to combine sounds for purposes of detection or loudness perception. It is not the frequency resolution of hearing, as it relates to the perception of timbre, which is much higher
Critical Distance The distance from a sound source in a room at which the direct sound and the reverberant sound are equal in level
Crossover Electrical filters that direct the appropriate frequencies to the woofer, midrange, tweeter, etc. in a loudspeaker system. The crossover frequency is the frequency at which the loudspeaker driver being turned off (e.g. a woofer) is at the same sound level as the one being turned on (e.g. a tweeter).
Crossover Frequency See crossover
Crossover Slope The rate, expressed in dB per octave, at which audio signals are attenuated as frequencies move into the crossover range. A high attenuation rate, e.g. 24 dB/octave means that there is little interaction between adjacent loudspeaker drivers. Low attenuation rates, e.g. 6 dB/octave allow adjacent drivers to operate simultaneously over a wide frequency range. See: Crossover, Octave
Crosstalk Unwanted sound from one channel that leaks into another
CRT An abbreviation for cathode ray tube. A device in which a finely focused beam of electrons scans the phosphor coated front surface of a picture tube causing changes in brightness according to the current flow in the beam. Multiple beams can energize different colored phosphors for color video displays. Used in direct view televisions and projection units.
Curvilinear Cone A diaphragm with a reducing curvature from center to edge, used to achieve specific performance objectives
C-weighting See Frequency Weighting
cycles per second The frequency at which a periodic event, such as alternating current, occurs. Now called Hertz, abbreviated Hz
D/A Converter A device that accepts a digital signal as an input and converts it to analog form at its output
D2B Optical This Digital Data Bus (D2B) was developed by Becker in 1995 in collaboration with Philips and C&C Electronics. D2B Optical was the first fiber-optic data transmission system to be used for audio and control data in vehicles with a data rate of approximately 5Mbit/s.
DAB DAB (Digital Audio Broadcasting) is a technology standard for broadcasting audio using digital radio transmission. The term digital radio was first used for DAB in 2001
DAC See D/A Converter.
Damping Reducing the energy in a vibrating or resonating system by adding electrically, mechanically or acoustically lossy materials or devices
Damping Factor In power amplifiers, it is a measure of the output impedance of the device. Expressed as a number arrived at by dividing the impedance into 8 ohms. For example, an amplifier with an output impedance of 0.04 ohms would have a damping factor of 8/.04=200. This, and higher numbers are common for solid state amps. Tube amplifiers have much higher output impedances and lower damping factors. In practice, the output impedance of the amplifier has almost no effect on loudspeaker damping, but it can have a significant effect on the frequency response of loudspeakers, most of which have frequency-dependent impedances. Within reason, higher numbers are better
DAT Digital Audio Tape. A popular version is R-DAT which employs rotary heads, as is done in VHS video recorders, but on tiny cassettes. Signals are digitally encoded
dB see Decibel.
DBO Dynamic Bass Optimization)A high pass filter with variable cutoff frequency and variable Q, designed to enhance the performance of subwoofers mounted in sealed and vented enclosures. DBO provides bass boost and protection from overexcursion at the lowest frequencies simultaneously
DC Direct Current. A condition in which the polarity of the voltage is constant, and current flows only in one direction. Batteries and rectified AC power supplies are examples of DC power sources
Decade A factor of ten. In frequency, humans can hear a range of about 3 decades: 20-200, 200-2000,2000-20,000 Hz
Decibel A logarithmic measure of relative voltage, current or power. A decibel is one-tenth of a bel, abbreviated dB. In terms of power, 3 dB = 2x, 10 dB = 10x. In terms of current or voltage: 6 dB = 2x. In terms of perceived loudness: 1 dB is just audible, a 10 dB sound level change represents double or half loudness
Demo Demonstration
Diaphragm The vibrating portion of a loudspeaker driver that radiates sound. In woofers, diaphragms are commonly conical in shape. Tweeters are often dome shaped. Midrange speakers can be either
Diaphragmatic Absorbers Sound absorbers that remove energy from a sound field by making it do work, moving a surface. Most effective at low frequencies. Vibrations in walls, floors, ceilings, windows, etc are all indications of diaphragmatic absorption at work. Sometimes it is necessary to add custom built units to absorb more energy at specific low frequencies in order to control room resonances. See: Resistive absorbers, Reactive Absorbers
Die Cast Aluminum Baskets Driver baskets that are cast from aluminum. Cast baskets are much stronger than stamped steel and allow for tighter production tolerances and precise driver operation under even the most demanding situations
Diffraction When the direction of a sound wave is changed by obstacles or geometric changes in the sound path. Not to be confused with reflection or refraction. Hearing sound around a corner is an example. In loudspeaker systems, sound is diffracted by the edges of a baffle, in an amount depending on wavelength and the size and shape of the edge. It is a factor in the design.
Diffuse Sound Field A sound field in a room that, at any point in the room, has equal energy arriving from all directions. This is an idealized concept that, in practical listening spaces, is never perfectly realized
Diffuser An acoustical device, or surface that, by its shape causes incoming sounds to be reflected outward in many different directions
Diffusion A lack of directional order in a sound field. More reflections from more directions add diffusion
Digital The representation of a quantity in numeric form, normally in binary. In audio, this means that waveforms of sounds are sampled at very high frequencies, and each sample is stored in numeric form, so that the waveform can subsequently be reconstructed. See A/D converter, D/A converter, Analog
Digital Light Processing Developed by Texas Instruments, the heart of this image projection device is a semiconductor chip, operating as a light switch. It contains a rectangular array of hinge-mounted microscopic mirrors; each of these micromirrors measures less than one-fifth the width of a human hair, and corresponds to one pixel in a projected image. Single-chip devices use a color wheel to reproduce color, while three-chip devices dedicate a chip to each of the primary colors, red, green and blue
Digital Multimeter A meter that measures voltage, current, and resistance, and displays the result in numerical form
Digital Satellite System A broadcast system in which digital video and audio signals are delivered to customers' homes by means of signals radiated from a satellite in stationary orbit and received by a small dish antenna
Digital Signal Processor see DSP
Digital Television A generic term that describes any of several systems capable of delivering digital video signals. High Definition (HDTV), Intermediate Definition (IDTV), Enhanced-Definition (EDTV) and standard definition (SDTV) are some of the systems. See: HDTV, IDTV, EDTV, SDTV.
Digital-to-analog converter See D/A Converter
D-ILA D-ILA = Direct Drive Image Light Amplifier. A development of the original light valve in which the reflectivity of the polarized liquid crystal surface is controlled directly by pixels arrayed on a semiconductor backing. Each pixel can be addressed individually. Hence an alternative description has evolved Liquid Crystal on Silicon, or LCOS. The technology allows for a very high aperture ratio, meaning that the pixels are harder to see. See: ILA, Light Valve, Aperture Ratio, Projector
DIN Stands for: Deutsches Institut für Normung e.V., the German Institute for Standardization. In audio we find such things as DIN connectors, and car audio head units with DIN specified dimensions.
Diode An electronic device that blocks current flow in one direction, but allows it in the other.
Dipole Classic definition: a loudspeaker that radiates sound from both the front and back faces of the diaphragm. The forward and backward radiated sounds are therefore of opposite polarity (out-of-phase), and they cancel each other when they meet at the +/- 90 degree axes, producing acoustic nulls. The radiation pattern is nominally that of a figure 8. This also applies to microphones, in terms of their directional sensitivity. Contemporary usage: a loudspeaker with bidirectionally aimed drivers that are connected out-of-phase. Since the drivers are not coincident, the null is not perfect, and the off axis frequency response can be very irregular
Direct Sound Sound that arrives at a listener's ear (or a microphone) directly from the sound source, without reflection
Direct Subwoofer Input A connection bypassing the internal crossover of a subwoofer, to allow the connection of A/V receivers and surround processors that already contain their own subwoofer crossovers and adjustments. See: Crossover
Directional Interconnects/Wire Since audio is an alternating (AC) signal, overall the electrons in wires will spend exactly half of the time moving in one direction, and half of the time moving in the other. They end up where they started. Since there is no net flow of current, there can be no directional preference in the conducting wires. If there were directional behavior in interconnects or speaker wire, we would have the beginnings of diode behavior, meaning that one half of the audio signal would be distorted - clearly not a good idea. This is part of the 'smoke' of audio. There is, however, one legitimate situation where the orientation of an interconnect matters, and that is if one ground connection has been broken to eliminate a ground loop. In this case the end with the attached ground should be plugged into the signal source. See: Alternating Current, Ground Loop, Unbalanced Connection, Diode
Directivity A measure of the angular dispersion of sound radiating from a loudspeaker. It is known that, for good sound in rooms, loudspeaker system directivity should be relatively constant over most of the frequency range. See: Directivity Index
Directivity Index A numerical representation of the sound dispersion characteristics of a loudspeaker, expressed in dB. It is the difference between the measured on-axis frequency response and the sound power. 0 dB describes an omnidirectional loudspeaker, radiating sound equally in all directions. Increasing numbers describe an increasing bias for sound radiated in the forward direction. See On Axis, Sound Power, Directivity
Discrete In the audio context, discrete refers to sound recordings in which all channels are stored separately. Each channel is completely independent of each other channel
Discrete 5.1 media Discrete 5.1 media include DVD-Audio, DVD-Video and DTS-CDs. The popular 5.1-channel digital formats, like Dolby® Digital and DTS®, have three front channels (left, center and right) and two surround channels, all of which are full bandwidth, and a “.1” channel that is low-frequency only, and used for occasional special effects
Discrete Circuitry The use of separate components such as transistors, resistors, capacitors, and diodes in an electronic circuit instead of IC's (Integrated Circuits) in which these components are fabricated in microscopic size on a silicon chip. Performance and economic factors usually determine which alternative is chosen
Discrete Logic 7® technology See Logic 7 technology
Distortion When an audio signal has been changed by the nonlinear behavior of the microphones, electronics, and loudspeakers. The nonlinearities, whether acoustical, mechanical or electrical, change the audio signals which are passed through them. See: Linear Distortion, Non-Linear Distortion
Diversity Reception An antenna system, occasionally used in cars, employing two or more antennas in a system that constantly seeks out the one(s) with the strongest signal. Advantageous in difficult FM reception areas, like downtown in cities where multipath problems abound. See: Multipath
DLP See: Digital Light Processing
DMM see Digital Multimeter.
Dolby Pro Logic® An active matrix decoder for Dolby® Surround (Lt, Rt) signals outputting four audio channels (left, center, right and surround). See: Matrix Encode/Decode, Dolby® Surround, Dolby Pro Logic® II
Dolby Pro Logic® II A development of Dolby Pro Logic® in which there is some separation introduced into the two surround audio channels, as well as several other playback options, some of which apply to the playback of stereo music
Dolby® See Dolby® Digital; Dolby® Pro Logic®; Dolby ProLogic® II; Dolby® Stereo; Dolby® Surround; Dolby® B, C and S
Dolby® B, C and S Noise reduction systems developed by Dolby Laboratories, and widely used in tape record/play devices
Dolby® Digital An audio signal encoding/decoding system, developed by Dolby Laboratories, that uses perceptual coding to reduce the data rate required to transmit, and the amount of digital space required to store, digital audio signals. Different consumer and professional versions use different amounts of compression, and therefore have different levels of audio quality. It can store mono, stereo and multichannel formats. See Perceptual Coding
Dolby® Digital (audio coding 3/AC-3) An audio signal encoding/decoding system, developed by Dolby Laboratories, that uses perceptual coding to reduce the data rate required to transmit, and the amount of digital space required to store, digital audio signals. It can store mono, stereo and multichannel formats. Different consumer and professional versions use different amounts of compression and, therefore, have different levels of audio quality. See Perceptual coding
Dolby® Stereo The name commonly given to Dolby® Surround as it is used in movie theaters
Dolby® Surround A multichannel audio signal that has been matrix encoded for storage in two channels, called Left total and Right total (Lt,Rt). This is not a discrete system, as it incorporates a lot of crosstalk (sounds from one channel leaked into the others). The name also was used in early decoders that did not incorporate active steering to enhance the channel separation. See: Crosstalk, Channel Separation.
Dome Loudspeaker A loudspeaker driver having a diaphragm shaped like a dome. Commonly used for tweeters and midrange units
Double-Blind Listening Test A listening test in which the listeners are not aware of the product identities (the first 'blind') and the person conducting the test also is unaware of, or has no control over, which products are being auditioned at any given time (the second 'blind'), and therefore cannot influence the results
Downmix Generally, the process of combining several channels of information into a smaller number of channels. Specifically, a feature of some Dolby Digital playback devices, allowing users to convert the multichannel digital audio into a two-channel Dolby ProLogic compatible signal (Lt, Rt), or a stereo signal, or a mono signal. In all of these downmixes the LFE channel is not included, therefore the downmixed signals are not exactly the same as the original. See: Dolby Digital, LFE, Lt, Rt
downmixing The process of converting a program created in a multichannel format so that it can be played through a system with fewer channels, e.g. 5.1 to stereo
DRC See: Dynamic Range Contol
Driver Another name for a raw speaker or transducer, such as a woofer, midrange or tweeter. See: Compression Driver
DRM DRM (Digital Radio Mondiale) is a digital radio system for short-, medium- and long-wave. Compared to conventional AM radio, DRM can fit more channels, at higher quality, into a given bandwidth
DSP Digital Signal Processing. Any form of manipulation performed on an audio or video signal while it is in digital form. The term DSP acquired an unfortunate reputation when, in the early days, it came to be associated with artificial reverberation (hall, stadium, etc.) effects that could be added in during playback. Many of these effects were not good. Now, the quality of DSP processing is undisputed, and limited only by the competence of the programmers.
DSS See: Digital Satellite System
DTCP DTCP (Digital Transmission Content Protection) is a digital encryption method that enables the transport of content-protected audio and video signals via a digital transmission channel from a source (e.g., DVD player) to an end point (e.g., amplifier or display).
DTS® An audio signal encoding/decoding system, developed by DTS, Inc., that uses perceptual coding to reduce the data rate required to transmit, and the amount of digital space required to store, digital audio signals. It can store mono, stereo and multichannel formats. Different consumer and professional versions use different amounts of compression and, therefore, have different levels of audio quality. See Perceptual coding
DTS-CDs DTS-CDs are music CDs produced with five discrete channels for playback in multichannel format through suitable decoders
DTV See: Digital Television
Dual Cone A speaker that includes a small cone attached to the apex of the woofer cone. At high frequencies, where the woofer cone is unable to respond to the movement of the voice coil fast enough, the small cone vibrates and helps to augment the high frequency response of the speaker. Dual-cone speakers are often used in enrty-level car-audio systems
Dual Voice Coil A speaker that includes two voice coils wound on the same voice coil former. The two voice coils, connected in either series or parallel provide a choice between two total impedance values
Dubbing In film sound, the act of mixing or re-recording components that make up a sound track is called dubbing
Dull In sound quality: the opposite of 'bright', implying a deficiency of high frequency sounds.
DVC (Dynamic Volume Control) In car audio systems, this adjusts the volume and frequency response of the playback to compensate for the auditory masking effects of road, aerodynamic and mechanical noises in a moving vehicle
D-VCR A video cassette recorder (VCR) which can record digital audio and video signals on standard VHS tape
DVD Initially interpreted as meaning Digital Video Disc, but now that there are several uses for the medium, it is more popularly known as the Digital Versatile Disc
DVD, DVD-Video DVD initially stood for Digital Video Disc but, now that there are several uses for the medium, it is more popularly known as the Digital Versatile Disc
DVD-A (DVD-Audio) An audio version of DVD, in which multiple digital audio channels can be stored in uncompressed PCM form, or using a lossless compression algorithm (the digital audio signals are reconstructed without alteration). The massive storage capacity of DVD allows for many options
DVD-Audio An audio version of DVD, in which multiple digital audio channels can be stored in uncompressed PCM form, or using a lossless compression algorithm (the digital audio signals are reconstructed without alteration). The massive storage capacity of DVD allows for many options
DVD-Video DVD with a special directory structure for files that contain uncompressed or compressed audio signals, and still or moving images plus optional subtitles. Usually protected by various digital copy protection measures
DVI Digital Visual Interface. A standard created to convert analog signals into digital signals to interface with both analog and digital monitors. It handles bandwidths in excess of 160 MHz and thus supports UXGA and HDTV. Common in computers and some television and video products. Currently (2003) being combined with HDCP, a copy-protection scheme, for connections between some video sources and displays. See: HDCP, UXGA, HDTV.
DVR Digital Video Recorder. A device that records and plays back streaming audio and video signals using a digital hard drive for storage
DX A short form for 'distance', referring to radio reception. Some radios have local/DX settings to optimize performance when close to or far from the transmitters
Dynamic Range The difference between the loudest and softest sounds that can be reproduced by a device or format. Usually expressed in dB
Dynamic Range Control DRC is a feature of some Dolby Digital decoders which enables users to reduce the dynamic range of the sound so that late-night listening need not disturb others in the house, or neighbors. See: Dynamic Range
Early Reflections Those sounds that arrive at a listener's ears after one reflection from a room boundary.
Echo A reflected sound that arrives after a delay sufficient for a listener to distinguish it as a discrete event in time. In rooms this is modified by the reverberation time of the space
Edge-driven Dome Tweeter A tweeter that uses a voice coil wound around a voice coil former that has the same diameter as the tweeter's radiating area. Edge-driven tweeters often provide higher power handling than balanced, or W-Dome tweeters
Edgewound Ribbon Voice Coil A loudspeaker voice coil that is made from wire flattened into a metal ribbon and then wound on edge. This maximizes the amount of wire in the magnetic gap, improving the performance of a loudspeaker motor
EDTV See: Enhanced-Definition Television
Efficiency The measure of a device's ability to convert input power to work. Expressed as a percentage. See: Sensitivity
Electrolytic Capacitor A common form of capacitor consisting of a conductive film in an electrolyte. Tends to be used for larger values of capacitance
Electromagnet A magnet consisting of wire wound around a soft iron core. It becomes an active magnet when current is passed through the wire, and it ceases to be a magnet when the current stops. See: Magnet
Electronic Crossover An electrical filter designed to limit the band of frequencies that is sent to the input of an amplifier connected to a loudspeaker designed to reproduce only a certain band of frequencies, i.e. a subwoofer, midrange driver or tweeter. See also Crossover
Electrostatic Commonly referring to loudspeakers in which a thin conductive membrane serves as the diaphragm driven by electrostatic forces generated between it and fixed perforated electrodes in front of and behind it. Requires a polarizing voltage, and high voltages to drive it. Electrically capacitive. Usually radiating a dipole sound field. Small maximum displacements limit low frequency output and necessitate large diaphragms, and consequent directivity issues. See: Dipole, Directivity
Elliptical Oblate Spheroidal™ (EOS™) waveguides Developed for the JBL Pro LSR studio monitors, EOS™ waveguides evenly disperse high frequencies for more precise stereo imaging over a wider listening area
EMC EMC (Electromagnetic Compatibility) refers to electromagnetic disturbance that occurs when different electronic devices are connected. See EMI
EMI Electromagnetic interference created when a device radiates electromagnetic waves that are received by other devices. Some kinds of electric motors, car ignitions and computers are notorious for radiating EMI. AM radio is a common indicator of EMI.
Enclosure The box, or other shape of volume, that accommodates the transducers in a loudspeaker system. Normally, its shape is dictated by the acoustical needs of the mid and high frequency drivers, and the volume is determined by the design chosen to complement the performance of the woofer. There are several options for low-frequency enclosures, closed, bass reflex, passive radiator, etc. See: Transducer, Driver, Woofer, Bass Reflex, Acoustic Suspension
Enhanced-Definition Television A broadcast system in which existing equipment is used to transmit an enhanced signal. It looks no different on standard television receivers but is enhanced when viewed on those with the extra feature
EOS™ Waveguide Developed for the JBL Pro LSR studio monitors, EOS™ waveguides evenly disperse high frequencies for more precise stereo imaging over a wider listening area
EQ See: Equalizer
Equal Loudness Contours Graphs displaying contours of equal perceived loudness for single frequencies or narrow band sounds. Each contour is referenced to 1 kHz, and shows the variations in physical sound level required to maintain equal perceived loudness at all audible frequencies. There have been several determinations, for different sounds, under different listening conditions. Fletcher and Munson, Robinson and Dadson, and Stevens are among the best known investigators. See Phon.
Equalization The process of using an equalizer to correct for problems in an audio system. The difficulty is to know what the problem is caused by, and whether it is the kind of problem correctable with an equalizer. Measurements are usually advised.
equalization A feature of the THX Home program, in which high frequencies are attenuated to compensate for excessive high frequencies in many movies. Problem is that it is a fixed equalization, and not all movies need the same amount of compensation, or any at all. Concert programs usually need none. It is a feature that should be easily accessible for turning on and off, but often is not. A treble control is an imperfect alternative as they usually start attenuating at too low a frequency.
Equalizer A device consisting of adjustable filters that can change the frequency response of an audio system. Equalizers can compensate for frequency response aberrations in loudspeakers, loudspeaker/room combinations, and also for adjusting the tonal balance of recordings. See also: Graphic Equalizer, Parametric Equalizer, Tone Controls
Excursion The in and out movement of a loudspeaker diaphragm
Extended Pole Piece A form of loudspeaker motor design in which the front of the pole piece is extended to improve the uniformity of the magnetic field within which the voice coil moves. This reduces distortion at large excursions
EzSet™ EzSet™ uses a built-in sound pressure measurement and calibration system that lets you automatically balance speaker channel levels for optimum surround sound enjoyment – regardless of the speaker type or room conditions
F Connector A cylindrical, often threaded, connector in which the central wire in a coaxial cable is used as the center pin. Widely used for cable and antenna connections in television.
Fader In car audio, the front-to-back sound level adjustment
Far Field Moving away from a sound source, the far field is the region in which the sound level drops 6 dB for each doubling of distance. The larger the sound source, the farther away the far field begins. When measuring loudspeakers it is necessary to be in the far field, otherwise the frequency response will be different for every measuring distance. Normally, 2 meters or more is required. See Sensitivity
Farad The basic unit of capacitance
Fast Fourier Transform A computationally very efficient way to calculate a Fourier Transform. See: Fourier Transform
Feedback In Amplifiers: the practice of connecting (feeding back) a portion of the output signal to the input so that it can be compared to the input signal and errors corrected. The signal must be inverted (negative feedback) to prevent oscillation, or uncontrolled, very loud, howling (positive feedback). Positive feedback is sometimes experienced in public address systems as a ringing or howling when too much of the amplified sound is picked up by the microphones
FEM (Finite Element Method) FEM is a form of computer-aided modeling used in engineering. It is used to solve problems in many disciplines. The area or volume to be analyzed is divided into a large number of small elements, and the behavior of each element is modeled by solving the large system of simultaneous equations. FEM is used to predict the behavior of materials and assemblies during the design phase, speeding the process and allowing for experimenting with different alternatives without having to construct prototypes
FFT See: Fast Fourier Transform
Fidelity See: High Fidelity
Field In a video display of interlaced scan lines there are two fields, presented alternately, one consisting of even-numbered lines, and the other of the odd-numbered lines. See: Interlace.
Fill Polyfill, glass or mineral fiber or something similar used inside a loudspeaker enclosure. Filling a closed box makes it seem acoustically larger to the woofer, and in all boxes, fill damps standing waves within the box.
Flat Response Refers to a flat, or linear, frequency response, meaning that an audio component can reproduce all audio frequencies at the same, correct, level. See Frequency Response
Fletcher and Munson Scientific pioneers in the investigation of perceived loudness as a function of frequency and sound level. See: Loudness Contours','Glossary',775,400,'right')" class="link">Equal Loudness Contours
Flush mount A speaker mounting system that places the front of the speaker on nearly the same plane as the speaker's baffle
Flutter Acoustical: a rapid succession of reflected sounds occurring between two parallel surfaces, normally stimulated by a transient sound such as a hand clap. Electronic: in recording media, especially analog tape, a periodic variation in pitch caused by uneven motion of the tape.
FM see Frequency Modulation
Foley Effects Sound effects of all kinds, wind, footsteps, door slams, telephones, gunshots, etc. that are added to a movie soundtrack
Foot-Lambert A measure of picture brightness. 1 Foot-Lambert is 1 lumen per square foot of screen surface. The SMPTE (Society of Motion Picture and Television Engineers) specification for a film-type movie theater is 16 foot-Lamberts of brightness, a level not always achieved. Direct-view televisions can be as high as 30 foot-Lamberts
Fourier Transform Developed by a French mathematician in the early 1800's, the Fourier transform basically separates a waveform into sinusoids (pure tones) of different frequencies, storing the data as amplitude and phase as a function of frequency. These sinusoids can be added together to reconstruct the original waveform. The transformation, therefore, is between the time-domain waveform and the frequency-domain spectrum of a signal or sound. Both are complete descriptions of the signal, and one can be computationally converted into the other. See: Transform, Spectrum, Transfer Function. Impulse Response, FFT, Spectrum Analyzer.
Frame In video, the portion of a signal that contains all of the scan lines that comprise one image. Interlaced systems have two fields per frame. See: Interlaced, Field.
Free Air Resonance The natural resonance frequency of a loudspeaker driver when it is suspended in "free space".
Free Field See Anechoic.
Frequency The number of vibrations or cycles completed by a signal in one second. Frequency is expressed in cycles, or more commonly, Hertz (Hz).
Frequency Modulation A method of radio broadcasting in which the radio carrier frequency is frequency modulated by the audio signal. Capable of high sound quality, and relatively immune to interference and static. However, it propagates poorly over long distances and suffers from multipath interference and shadow zone problems in cities and hilly areas
Frequency Response A measure of the amplitude vs. frequency performance of an audio component, measured from its input to its output. A perfect electronic device should have a flat, or linear, frequency response over its useful frequency range, indicating that it reproduces all frequencies at the correct level. Loudspeakers are more complicated since the output is sound which is radiated in all directions. It is necessary to measure the frequency response at many locations all around the loudspeaker in order to be able to predict how it may sound in a room. For loudspeakers, there is no single frequency response measurement that is completely descriptive of its performance. See: Transfer Function, Spectrum
Frequency Weighting Used in measurement of overall sound levels to take account of the frequency-dependent loudness characteristics of ears at different sound levels. A-weighted measurements attenuate sounds below about 1000 Hz (low sound levels), B-weighting rolls off frequencies below about 200 Hz (middle sound levels), and C-weighting rolls off below about 50 Hz (high sound levels). All three weightings roll off high frequencies above about 7 kHz. Sound levels measured using these weightings are designated dB (A), dB(B), dB(C), as opposed to unweighted (linear) measurements of sound pressure level (SPL).
Front Projector A projector that delivers an image to the front surface of a reflective screen allowing the audience to view the reflected image. See: Rear Projector, RPTV.
Fundamental The lowest in a series of harmonically related sounds. In musical sounds, it is the basis for all higher harmonics. In acoustically or mechanically resonant systems, it is the lowest of all resonant modes. See: Missing Fundamental
Fuse A device designed to protect other electronic devices by melting and opening the circuit when the system is drawing too much power. If a fuse blows it must be replaced with an identical part, otherwise future protection may be compromised. See: Circuit Breaker
Fusion Zone A horribly abused term, evolving from misinterpretations of the Haas effect, implying that all sounds arriving within an interval of time, ranging from about 20 to 50 milliseconds, are perceptually fused or integrated. This is wildly simplistic at best, and totally wrong at worst, because within these time limits there are several levels of clearly distinguishable perceptions including spaciousness, timbre change, image shift, multiple sound images and, at large delays, echoes. See: Haas Effect
Gain AUDIO: The difference in amplitude between the input to a device, and the output. The amount of amplification applied to a signal. VIDEO: the difference between the brightness of an image projected on a screen, and the brightness of the reflected light. Screens can have gains greater or less than one. The amount of gain is related to the uniformity of brightness as viewers move away from the direct axis. High-gain screens tend to be more directional. The color of the screen material is another factor.
Graphic Equalizer An equalizer consisting of several identical percentage-bandwidth (e.g. fractional octave) filters covering the Frequency Range audio frequency range or portion thereof. For example: 30 one-third-octave filters would cover the frequency range from 20 Hz to 20 kHz. See: Parametric Equalizer.
Gray Scale A measure of how well a video display tracks the shades of gray between perfect black and white. It is an assessment of the quality of the high resolution black and white picture that underlies the lower resolution color information.
Ground An electrical connection to the earth, or a conductor or chassis serving as a common reference.
Ground Loop When multiple ground connections are made at separated points in an electrical system there is the possibility of voltages existing between the connecting points. The common result is hum and/or noises introduced into the audio signal. See: Balanced Connections, Unbalanced Connections.
Haas Effect Haas, a German researcher, determined that a delayed sound could be as much as 10 dB higher in level than the direct sound before it was judged to be as loud as the direct sound. This means that, in a public-address system, the sound from a delayed loudspeaker could be that much louder than the voice of the person speaking, before the audience was attracted to the loudspeaker rather than the person. See: Precedence Effect, Localization, Direct Sound, Fusion Zone.
Harmonic A tone that is a whole-number multiple of the original, or fundamental, tone. Numerically, the first harmonic is the fundamental. Harmonics are abundant in musical sounds, helping to give instruments and voices their distinctive qualities. When harmonics occur as a result of nonlinear distortion, they change the timbre of musical sounds and voices. See: Missing Fundamental, Overtones.
Harmonic Distortion The form of distortion that occurs when a nonlinear device is driven with a pure tone. See Harmonic, Non-Linear Distortion, Distortion.
HD Radio™ One of DAB’s competitors, HD Radio is a digital radio system for transmitting audio on the FM and AM bands. It was developed in the USA by iBiquity, a company founded specifically to develop this technology. In contrast to DAB, HD Radio is not only a digital system, but one that can be operated as a hybrid system with analog AM and FM radio.
HDCD High Definition Compatible Digital. An encode/decode process aimed at enhancing the performance of conventional 16-bit audio signals on compact discs.
HDCP High-Bandwidth Digital Content Protection is a specification developed by Intel Corporation to protect digital entertainment content across the DVI interface. See: DVI.
HDTV See: High Definition Television
Head Unit A factory or aftermarket car radio, possibly including a CD or cassette tape player.
Headroom The difference between the maximum, or peak, signal levels in a program, and the maximum level that the audio component is capable of. E.g. a movie sound track requires 100 watt peak output to satisfy a listener, but the listener is using a 200 watt power amplifier. There is 100 watts of headroom. Headroom is inaudible, but it is there in case it is needed. See: Loudness.
Hearing Level A measure of how the hearing threshold level for a specific ear relates to the statistical normal hearing threshold for people in general. Audiometers are calibrated to show 0 dB for normal, and some number of dB for hearing thresholds that have been elevated because of hearing loss. See Audiometer, Hearing Loss, Hearing Threshold
Hearing Loss A reduction in hearing sensitivity, or the ability to hear small sounds, that is caused by exposure to excessively loud sounds, age, illness, drugs, etc. Hearing loss can be temporary or permanent. Repeated temporary losses often lead to some amount of permanent loss.
Hearing Threshold The smallest sound that can be heard. Humans are most sensitive in the middle frequency range, showing progressively reduced sensitivity at low frequencies and greatly reduced sensitivity above about 20 kHz. This characteristic is highly individual, and it changes with age and exposure to loud sounds.
Hearing Threshold Level See Hearing Level.
Heat dissipation The property by which a device transfers potentially damaging heat to the surrounding air.
Helmholtz Absorber A sound absorbing panel designed with holes or slots acting as the masses in a Helmholtz resonance with the volume of air behind the panel.
Helmholtz Resonance The 'classic' acoustical resonator (named after the acoustic research pioneer) consisting of a mass of air bouncing on a volume of air acting as a compliance, or spring. The common example is the soda bottle resonance, excited by blowing across the mouth. The air in the neck of the bottle is the mass, the bottle is the compliance. Drinking more soda lowers the resonant frequency. Many practical applications. See: Bass Reflex, Resonant absorbers, Helmholtz Absorbers.
Hertz The basic unit of frequency also called cycles per second. The number of full cycles completed by an alternating signal in one second.
High Definition Television A video system with approximately twice the horizontal and vertical resolution of conventional NTSC television, and presented in a 16:9 aspect ratio. See: NTSC, Aspect Ratio, Resolution
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High-Pass Filter An acoustical device or electrical network that blocks frequencies below a designated point, and allows higher frequencies to pass.
Horn An expanding acoustical waveguide in front of a loudspeaker driver, or compression driver, that shapes the wavefront of the sound as it radiates away from the source. This allows designers to control vertical and horizontal dispersion characteristics, essential to achieving good audience coverage in sound reinforcement systems, and increasingly used to finesse the frequency-dependent directivity of consumer loudspeakers to improve sound quality. Being acoustical transformers, horns can also improve the acoustical efficiency of the drivers. See: Compression Driver, Driver, Directivity, Throat.
Hue The quality of a color, e.g. a red hue, green hue, blue hue. Tint.
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Hz Abbreviation for Hertz. See Hertz.
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ILA Image Light Amplifier. See: Light Valve, D-ILA.
Image See Imaging
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Impedance In electronics: the opposition to alternating current flow in a circuit or device. Properly expressed as a complex quantity, it is also simplified as a magnitude only. The latter is commonly used in describing the impedance of loudspeaker drivers and systems. There are also acoustical and mechanical impedances.
Improved-Definition Television A television receiver that can improve the appearance of a standard video signal by employing signal processing techniques such as line doubling.
Impulse Response A measure of the time domain response of a system, input-to-output, to a very brief transient signal at its input. The Fourier transform of this time-domain waveform is the frequency-domain transfer function. See: Transfer Function, Fourier Transform, FFT.
Inductance The property of a circuit whereby a change in current causes a change in voltage. The unit of inductance is the Henry: the amount of inductance required to generate one volt of induced voltage when the current is changing at the rate of one ampere per second. See Inductor, Coil.
Inductive Coupling When signals or noises are coupled magnetically into a wire or cable. This is the principle that allows transformers to function, a good thing, and that can let unwanted signals creep into parts of an audio system, a bad thing.
Inductor See Coil, Inductance.
In-Ear Headphones Tiny headphones that are inserted directly into the ear canal. See: Circumaural Headphones, Supraaural Headphones.
Infinite Baffle In theory, an infinitely large flat baffle, used to isolate the sounds radiated by the front and back surfaces of a loudspeaker diaphragm. In practice, a baffle that is large compared to the longest wavelength of sound radiated by the loudspeaker. Also, incorrectly, used to describe a closed-box loudspeaker enclosure.
Infotainment A media device that provides a combination of music or video playback and navigation, telephone, traffic, cellular communication and internet access
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In-phase Two signals having the same waveforms that are in perfect synchronization with each other. There is no phase difference between them at any frequency. The signals will add (constructively interfere). See: Acoustical Interference.
Input Sensitivity The voltage required at the input of an electronic device in order to produce the rated electrical output. For example: in power amplifiers, the input voltage needed to produce the rated steady-state output power.
Intensity See Sound Intensity.
Interference See: Acoustical Interference
Interlace A video display made up of two alternating fields, one that scans the even-numbered lines followed by one that scans the odd-numbered lines. The field repetition rate is normally tied to the local AC power line frequency e.g. 60 fields/second in North America, thus presenting a complete picture, or frame, 30 times per second. See: NTSC, PAL, SECAM, Scan Line.
Intermodulation Distortion Distortion created when a nonlinear device is driven by multiple tones. Intermodulation distortion products are complex multiples and submultiples of the test signals, making them more easily audible than the harmonic distortion products which are simultaneously created in such a test. Music, being a complex signal, generates abundant intermodulation distortion when processed by a nonlinear device. See: Harmonic Distortion, Non-Linear Distortion.
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Inverse-Square Law In a free sound field (no reflections) the sound level of a non-directional source will diminish by 6 dB for every doubling of distance from the source. In rooms this can only apply to the direct sound from some kinds of sources. See also: Far Field
In-Wall Loudspeaker A loudspeaker designed to function best when it is mounted flush with the surface of a wall or ceiling. Special mounting hardware is used, and some models incorporate mechanical vibration isolation to minimize the coupling of vibration to the wall itself.
IR Remote A remote control that communicates by means of Infrared (IR) light. Such controls need line of sight to the devices being controlled, or good optical reflecting surfaces to help the light signal to get there. See: RF remote.
Kaladex® Tweeter This breakthrough tweeter material is ideal for the new GTO Series. It is smooth and natural, and has incredible UV- and moisture-rejection properties, making it ideal for automotive use. In addition, these are not commonly used w-domes, but actually edge-driven domes with a larger voice–coil diameter, yielding increased power handling and low-end response.
Karaoke Audio devices that allow the connection of a microphone for sing-along activities. Special videos are available with missing vocal tracks, and showing the lyrics as a subtitle.
Keystone Distortion/Correction In front projectors, if the projector is tilted up or down relative to its design axis, the image will take on a trapeziodal shape, being narrower at the top or bottom than it should be. The common distortion comes from an upward tilt, making the image larger at the top, like the wedge-shaped keystone at the top of a stone arch - the last one to be placed and the one that holds the arch up. Some display devices allow this to be corrected, but there may be some picture degradation.
Kilo- A prefix meaning thousand. For example: one thousand Hertz is 1 kilohertz, abbreviated 1 kHz.
Laserdisc An optical disc, 12 or 8 inches in diameter, that can store video in analog form along with analog and digital audio signals in stereo and multichannel formats. The analog signals are frequency modulated. See: FM, CAV, CLV
LCOS Liquid Crystal on Silicon. A digital video display device using a liquid crystal surface the reflectivity of which is controlled by a pixellated solid state control device underneath it. See: D-ILA, Projector.
LED Liquid Crystal Display is one in which the reflectivity and/or transparency can be changed by the application of a voltage. It is divided into many tiny independently conrolled pixels. They are very common: digital watches, calculators, dashboards, computer screens, rear and front projection video displays, etc. Since they are used as light transmission devices in most applications, there are losses, and getting the control voltages to each of the pixels presents challenges in maximizing the aperture ratio. See: Aperture Ratio, Projector.
LEDE Low-Noise Blocking Converter. The active receiving element in a satellite dish antenna. Some systems may have two or three LNB's on one dish, each aiming at a different satellite.
Letterbox The method of displaying a widescreen image on a standard 4:3 aspect ratio display. The width of the image is the width of the display, but the height is less, meaning that there are black bars above and below - like a letterbox.
LFE See: Low-Frequency Effects
Light Valve A video display device in which a powerful light source is modulated by a 'valve' controlled by a much smaller, less powerful one, thus making it possible to project a very large image. The valve is a polarized liquid crystal device in which one surface reflects a powerful light in proportion to the amount of much weaker light falling on the reverse side. The contolling light can be an image created by a CRT. Three valves, red, blue and green, are necessary for color projection. Being analog, there is no pixel structure. Also known a ILA (Image Light Amplifier) by its creator Hughes/JVC. See: D-ILA, LCOS, Projector.
Line Doubler A video processor that can double the number of lines in a scanned display, making each of the lines smaller, and therefore less visible. One common form of line doubler converts an interlaced picture into a progressively scanned picture. See: Interlace, Progressive Scan, IDTV
Line Level A low-level audio signal. The kind of signal that is typically communicated between components using shielded interconnects with RCA type connectors. Sometimes called preamp level, to distinguish it from speaker level signals. See: Speaker Level
Linear Distortion Changes to the amplitude vs. frequency characteristic and the phase vs. frequency characteristic of a signal. Such distortions are assumed to be constant at all signal/sound levels. See: Non-Linear Distortion, Distortion.
Localization Assigning a perceived direction to a sound. A full description would include horizontal angle (azimuth), vertical angle (elevation) and distance. The size of the perceived sound image may also be a consideration.
Logarithm In common logarithms, representing a number by the power to which 10 must be raised to equal it. For example, 10 to the exponent (or power) 2 = 10 squared = 100. The log of 100 is therefore 2.
Logic 7 An active matrix multichannel audio processing system, originally developed by Lexicon® and now used in several Harman products. It converts, or upmixes, two-channel stereo signals into five- or seven-channel signals, allowing listeners to better experience the surrounding ambient sounds that are already in the stereo mixes. Discrete Logic 7 expands this capability to include upmixes of 5.1-channel recordings to seven channels. All of these systems may have modes optimized for movie and music soundtracks, and for conventional stereo music recordings. It is especially designed to maintain a solid front soundstage, while expanding the perceived ambience beyond the room walls. Automotive versions address the unique circumstances of listening within cars, with special processing, loudspeaker design and placement all contributing to a greatly enhanced listening experience. See Matrix Encode/Decode, upmix.
Logic 7® An active matrix multichannel audio processing system, originally developed by Lexicon® and now used in several Harman products. It converts, or upmixes, two-channel stereo signals into five- or seven-channel signals, allowing listeners to better experience the surrounding ambient sounds that are already in the stereo mixes. Discrete Logic 7 expands this capability to include upmixes of 5.1-channel recordings to seven channels. All of these systems may have modes optimized for movie and music soundtracks, and for conventional stereo music recordings. It is especially designed to maintain a solid front soundstage, while expanding the perceived ambience beyond the room walls. Automotive versions address the unique circumstances of listening within cars, with special processing, loudspeaker design and placement all contributing to a greatly enhanced listening experience. See Matrix Encode/Decode, upmix.
Logic 7® technology An active matrix multichannel audio processing system, originally developed by Lexicon® and now used in several Harman products. It converts, or upmixes, two-channel stereo signals into five- or seven-channel signals, allowing listeners to better experience the surrounding ambient sounds that are already in the stereo mixes. Discrete Logic 7 expands this capability to include upmixes of 5.1-channel recordings to seven channels. All of these systems may have modes optimized for movie and music soundtracks, and for conventional stereo music recordings. It is especially designed to maintain a solid front soundstage, while expanding the perceived ambience beyond the room walls. Automotive versions address the unique circumstances of listening within cars, with special processing, loudspeaker design and placement all contributing to a greatly enhanced listening experience. See Matrix Encode/Decode, upmix.
Loudness The perceptual correlate of sound level. Subjective perception of loudness is highly non-linear. Doubling or halving loudness requires about 10 dB change in sound level at middle and high frequencies. At low frequencies, it can be as little as 4 dB. The smallest audible change in overall loudness level is about 1 dB. 3 dB is just nicely audible. Loudness also depends on the frequency, bandwidth and duration of the sound. See: Loudness Contours','Glossary',775,400,'right')" class="link">Equal Loudness Contours.
Loudness Contours See: Loudness Contours','Glossary',775,400,'right')" class="link">Equal Loudness Contours.
Loudness Control A separate control or, more commonly, a switch-selected addition to a volume control, that causes bass frequencies to be amplified as the overall volume is turned down. The idea is to compensate for the fact that the ear becomes progressively less sensitive to bass at low sound levels. See: Loudness Contours','Glossary',775,400,'right')" class="link">Equal Loudness Contours.
Loudspeaker An transducer that converts an electrical signal into sound.
Loudspeaker System A set of transducers, with a crossover network, in an enclosure. A two-way system has a woofer and a tweeter, a three-way system adds a mid-range, and so on. Up to a point, more transducers allow a designer more capability in designing a good sounding system, but there are no guarantees. More transducers should, however, allow for higher sound levels. See: Woofer, Tweeter, Crossover, Enclosure.
Low Frequency Generally refers to sounds below about 300 Hz.
Low Frequency Effects The 0.1 channel in 5.1-channel Dolby Digital signals. All 5 main channels are full range, so this additional channel, covering the frequency range 3 Hz to 120 Hz is there to accommodate very loud low frequency special effects sounds, such as explosions. It is included in the bass managed subwoofer outputs of surround processors and receivers, but is discarded in the two-channel downmixes of Dolby Digital that occur in many DVD players. See: Downmix, Dolby Digital, Bass Management
Low Pass Filter An electronic or acoustical device designed to pass all frequencies lower than the design frequency, and to attenuate, or block, all higher frequencies.
LP recordings LP = Long Playing - relative to the 78 rpm discs of the previous generation. The familiar 12-inch diameter vinyl discs, containing analogue recordings played back at 33 1/3 rpm. Almost all are two-channel stereo, although some were encoded in four channel formats during the Quadraphonic era in the late 1970's.
LP recordings LP = Long Playing - relative to the 78 rpm discs of the previous generation. The familiar 12-inch diameter vinyl discs, containing analogue recordings played back at 33 1/3 rpm. Almost all are two-channel stereo, although some were encoded in four channel formats during the Quadraphonic era in the late 1970's.
Lt, Rt Left total, right total. Names given to the left and right channels of a two-channel audio signal which contains Dolby Surround encoded information. See: Dolby Surround.
Luminance Brightness, or the black and white content of a picture. The symbol 'Y' designates the luminance signal. Combined with chrominance (C) to complete a color video picture. See: Chrominance, Chroma.
M.T.S. Multichannel Television Sound. The common method of broadcasting stereo audio with a television signal.
Magnet Steel or other magnetic material that has been magnetized. A permanent magnet will hold its magnetization indefinitely. Used in loudspeakers to provide the static magnetic field within which the voice coil operates. See Voice Coil, Electromagnet.
Magnetic Shielding A design of loudspeaker motor in which the stray magnetic field is suppressed to avoid distortions to CRT, or other magnetically sensitive, video displays.
Masking Audio: A perceptual phenomenon in which the presence of one sound reduces our ability to hear another. Loud music may mask a doorbell. The music that creates distortion in a nonlinear device may prevent us from hearing all of the distortion created by the problem. VIDEO: The black area surrounding the picture area in a front projection screen. See Simultaneous Masking, Temporal Masking
Matrix Encode/Decode A method of electrically combining, or encoding, several channels of information into a smaller number of channels for communication or storage, e.g. Dolby Surround. The reverse matrix can be used to decode the original channels on the other end. However, channel separation between some of the channels can be as low as 3 dB, so the reconstruction is imperfect. Active or steered matrix decoders can enhance the separation when not all channels are operating simultaneously, making the effect seem to be more discrete (e.g. Logic 7, Dolby ProLogic). See: Channel Separation, Dolby ProLogic, Logic 7, Discrete.
Mega- A prefix meaning million. For example: one million Hertz is 1 megahertz, abbreviated 1 MHz.
Membrane Absorbers See: Diaphragmatic Absorbers.
Micro- A prefix meaning one-millionth. For example: one-millionth of a Farad is 1 microfarad, abbreviated 1 (NEED SYMBOL FOR MICRO)farad.
Midrange Frequencies between 300Hz and 3000Hz. See Midrange driver.
Midrange Driver A speaker that is designed to reproduce middle frequencies, from about 300 Hz to about 3000 Hz. This is where most speech and much musical information lies.
Milli - A prefix meaning one-thousandth. For example, a milliampere is one-thousandth of an ampere. Abbreviated ma.
Missing Fundamental A perceptual phenomenon in which listeners may perceive a low pitched sound when there is no physical sound energy at that frequency. Musical notes are combinations of a fundamental (the lowest harmonic) and a collection of harmonics. If only the fundamental is missing, as it might be in a sound system with poor, or no bass output, humans can still perceive the correct pitch for the note. Of course, the timbre is changed, and the tactile bass sensations are missing, but the essential tune will be there. See: Harmonic, Fundamental.
Mixing In audio recordings of all kinds, it is common for several 'tracks' of single instruments, voices, or sound effects to be combined, or mixed, into the final product. At the same time, equalization, reverberation and other electronic enhancements can be made to the recording.
MLP MLP (Meridian Lossless Packing), also known as Packed PCM (PPCM) or Dolby MLP Lossless™, is a proprietary lossless compression algorithm for digital sound recordings. The format was specifically designed for high-resolution audio data and is mandatory for DVD-Audio.
MMD Derived from our patented CMMD technology, Infinity's new Metal Matrix Diaphragms (MMD) continue the Infinity tradition of using advanced materials to improve sonic accuracy. By adonizing both sides of an aluminum core, we're able to significantly improve cone performance and outperform cones made of traditional materials.
Mode See: Room Resonances.
Monaural Literally, one ear, or listening through only one ear. Commonly used to describe a single channel or monophonic system or device, e.g. a single channel, monaural, amplifier. See Monophonic.
Monophonic A single channel system or component.
Monopole Classic definition: a sound source that is small compared to any wavelength that it radiates, and is therefore uniformly omnidirectional. Contemporary usage: a conventional forward-firing loudspeaker. Most consumer loudspeakers are small compared to the wavelengths at very low frequencies and so, at least at those frequencies, they qualify as true monopoles.
MOST® MOST® (Media Oriented Systems Transport). Digital network for the optimized transmission of data (particularly all multimedia data used in vehicles) via fiber-optic or electric cables. As with D2B Optical, the defining characteristic of MOST is synchronous data transmission, which coordinates sound and image signals. Many European and Asian vehicle manufacturers use MOST. The system was developed in 1997 by the MOST Cooperation, a consortium of Harman/Becker, Audi, BMW, DaimlerChrysler and SMSC; the consortium also works with other industry partners.
MOST® (Media Oriented Systems Transport) Digital network for the optimized transmission of data (particularly all multimedia data used in vehicles) via fiber-optic or electric cables. As with D2B Optical, the defining characteristic of MOST is synchronous data transmission, which coordinates sound and image signals. Many European and Asian vehicle manufacturers use MOST. The system was developed in 1997 by the MOST Cooperation, a consortium of Harman/Becker, Audi, BMW, DaimlerChrysler and SMSC; the consortium also works with other industry partners.
Motor The assembly on the back of a loudspeaker, consisting of a magnet, iron magnetic circuit elements, and a voice coil which together cause the diaphragm to move in response to an electrical audio signal from a power amplifier.
Moving Coil Loudspeaker A conventional loudspeaker driver in which a diaphragm is driven by a voice coil. See: Motor, Voice Coil
MPEG MPEG (Motion Picture Experts Group) develops standards for the compression of digital audio and video signals. There are different MPEG standards, depending on the application. MPEG-2 is the video standard used for DVDs; the correct name for the popular term MP3 is MPEG-2 audio, layer 3.
MPEG (Motion Picture Experts Group) MPEG develops standards for the compression of digital audio and video signals. There are different MPEG standards, depending on the application. MPEG-2 is the video standard used for DVDs; the correct name for the popular term MP3 is MPEG-2 audio, layer 3.
MPEG Audio MPEG-1 is a perceptual coding algorithm for two audio channels. MPEG-2 does multichannel audio. See: Perceptual Coding
MPEG Video MPEG-1 is a data compression algorithm for low-quality video, such as that on Video CD. MPEG-2 is used for DVD and HDTV. See:
Multichannel A sound recording/reproduction system with more than two channels and loudspeakers. Current systems have 5, 6 or 7 channels plus a low-frequency effects (LFE) channel. Multichannel sound can also be simulated from two-channel sources. See Logic 7, Dolby ProLogic Plus.
Multimeter An analogue or digital meter capable of measuring voltage, current and resistance.
Multipath When a radio or television signal arrives at a receiver from two or more different paths (at least one of which is a reflection) the signals interfere with each other causing distortion in FM audio and ghosting in television pictures. See: Diversity Reception.
Multiroom A feature of custom whole-house systems, and of some AV Receivers, allowing sound to be delivered to loudspeakers in other rooms, without interfering with what is happening in the main entertainment room.
Multi-way loudspeaker A loudspeaker system in which different drivers handle different parts of the frequency range. E.g. two-way = woofer + tweeter, three-way = woofer + midrange + tweeter.
Music Power A non-standard power rating used mostly for amplifiers, trying to bridge the gap between the relatively low steady-state (RMS) power rating, and the much higher peak power rating. Both are repeatable, but unrealistic in terms of representing what happens with music. However, since music is so variable, there can be an infinite number of music power ratings.
Mute, Muting A button or control that, in one operation, reduces the sound level by a fixed amount. Depending on the equipment, the sound can be completely turned off, or simply attenuated by a chosen amount. Useful for relief from commercials and for answering the telephone.
Navigation A device that uses GPS (Global Positioning System) to provide route mapping and directions
NC Rating See: Noise Criteria
Negative Feedback See Feedback.
Neodymium A rare earth magnet that is several times more powerful than conventional materials such as ferrite. This allows for very compact loudspeaker motors, which can be designed to be self shielding to minimize interference with CRT video displays. See Motor, Magnetic Shielding.
Noise Cancellation The process by which a signal processor samples ambient noise through a microphone and inserts the inverse of the noise into the playback signal. Often used in industrial settings to reduce noise from machinery or other steady-state noise. It's now being applied to in-car audio systems to reduce ambient noise caused by the movement of the vehicle.
Noise Criteria In acoustics, normally used to describe a rating system for evaluating noise from heating, ventilating and air conditioning (HVAC) systems. It has come to be used as a basis for evaluating and establishing requirements for background noise in listening spaces. Based on a set of sound level vs. frequency curves known as the NC criteria. The lowest curve that the spectrum of the measured sound does not exceed is defined as the noise criterion (e.g. NC-30) for that room. There are other variations on this theme, adopted for different purposes, or in different parts of the world (e.g. NR - noise rating - in Europe).
Noise Reduction Coefficient A simplified rating of the sound absorbing properties of materials, in which the sound absorption coefficients at 250, 500, 1000 and 2000 Hz are averaged. Abbreviated: NRC. Obviously this is of no value in evaluating what happens at low, or very high frequencies. It is a speech-oriented measure. See: Sound Absorption Coefficient.
Nominal Impedance The stated impedance rating of a speaker, used by manufacturers to represent the load the speaker will present to an amplifier. In fact, the impedance of most loudspeakers varies considerably with frequency, so the nominal impedance is only a very rough guide. In practice, the minimum impedance also needs to be known.
Non-Linear Distortion An undesirable characteristic of a device in which audio signals are modified, and modified differently at different sound levels. Usually, the problem increases in magnitude with increasing level, although there are some problems that are more noticeable at low levels. The audible significance of the nonlinearity is evaluated by applying test signals and measuring the harmonic and intermodulation distortion products that are added. See: Linear Distortion, Harmonic Distortion, Intermodulation Distortion.
NR Rating SEE: Noise Criteria.
NRC See: Noise Reduction Coefficient.
NTSC Stands for National Television Standards Committee, which set the television broadcast standard for North America, also used in much of Central and South America, the Carribean Islands, Japan and Taiwan. It is a 525 line interlaced raster-scanned system displayed at 60 fields/second. Of these, about 480 lines contain picture information. See: PAL, SECAM, Television Systems
O.E. Original Equipment see also OEM
Oblique Modes See Room Resonances.
Octave A doubling or halving of frequency. Example: 80Hz is one octave above 40Hz. In measurements and audio analysis, it is common to examine what is happening within octave or fractional-octave bands. 1/3 octave band analysis is very common, with new instruments capable of even higher resolutions. See: Real-Time Analyzer, Spectrum Analyzer.
OEM Original Equipment Manufacturer. When one company supplies systems or components to another manufacturer for installation at the time of manufacture. For example, Harman supplies many automobile manufacturers with audio, video, navigation and other systems and components on an OEM basis. See: Aftermarket.
Ohm Basic unit for measuring resistance and impedance.
Ohm`s Law The basic relationship between current, voltage, and resistance. Ohm's law states that voltage = current x resistance, current = voltage/resistance, and resistance = voltage/current.
Omnidirectional Referring to microphones or loudspeakers, having equal sound sensitivity or output, respectively, in all directions.
On Axis In a loudspeaker it is the imaginary axis that projects perpendicular to the plane of the loudspeaker drivers. Normally it originates at the tweeter axis, or at a point close to the tweeter and midrange drivers.
Oscillator See: Audio Oscillator
OTA Meaning Over The Air. See: Terrestrial.
Out-of-phase Two signals having the same waveforms that are in perfect synchronization with each other but with a perfect 180-degree phase shift at all frequencies. Equivalent to a polarity inversion of one signal. The signals will cancel each other (destructively interfere). See: Acoustical Interference, Polarity Inversion.
Overtones Sounds with frequencies that are higher than the fundamental frequency and that normally occur with the fundamental. The first overtone is the second harmonic, since the first harmonic is the fundamental. See: Harmonic.
PAL The television broadcast coding standard used in England, Europe, and many countries in the rest of the world. It has 625 lines displayed at 50 fields/second. Of these, about 576 lines contain picture information. See: NTSC, SECAM, Television Systems.
Pan and Scan A method of converting widescreen programs and movies for viewing on a standard 4:3 aspect ratio television. It involves rerecording the program while panning and scanning (sweeping left and right) with a camera, selecting the portion of the picture to be shown in the reduced size. Obviously, the result is not the same movie that the director created, but it fills the entire TV screen. Letterboxing is the alternative. See: Letterbox, widescreen, aspect ratio.
Parallel Connection Connecting two or more devices across the same terminals so that each device carries the full applied voltage. In loudspeakers, parallel connection of two identical units halves the impedance seen by the power amplifier, which can create problems with amplifiers not able to drive low impedances. For example, two 6-ohm loudspeakers operating together will present a 3-ohm load, which is below the safe operating load range for many power amplifiers. This is a consideration in the A, B, A+B loudspeaker switching feature of A/V receivers. See Series Connection.
Parametric Equalizer An equalizer consisting of several filters each of which can be adjusted in each of three parameters: frequency, bandwidth or Q, and amplitude, allowing it to closely match the properties of resonances which are to be attenuated. See:Resonance, Graphic Equalizer.
Particle Velocity Air is constantly in motion due to wind or thermal convection currents. The particle velocity of interest in audio is that which is added by the alternating pressure fluctuations of sound as it passes through. Due to sound alone, particles stay in place and simply vibrate.
Pass Band See Bandpass.
Passive Radiator Often called a "drone cone." A diaphragm with a suspension but no motor assembly. Passive radiators can be substituted for a vent or port in a speaker.
PCM A straightforward, uncompressed coding method in which analog signals are sampled at regular intervals, and each sample is represented by a digital number representing the amplitude at that instant in time. Sampling is done at a frequency at least two times the highest frequency of interest, and the digital number must have a sufficient number of bits to capture and reconstruct the essential qualities of the audio signal (dynamic range, low distortion and noise, etc.). For example, typical CDs are recorded using a sampling frequency of 44.1kHz, using a 16-bit digital number. See Bit, Compression.
Peak In time: the instantaneous maximum value of a time-varying quantity. E.g. peak power in power amplifiers. In frequency response: an elevated output that is concentrated over a narrow range of frequencies, describing a peak in the frequency response curve.
Perceptual Coding A method of processing a digital audio signal in which knowledge of auditory masking is used to predict what portions of the signal would not be heard by normal listeners. These portions are then either discarded, or more simply encoded, so that the data rate used to communicate the signal is reduced, as is the storage capacity. Several such "lossy" coding systems exist, and they all sound excellent at high data rates, degrading by different amounts in different ways as the data rate is reduced.
Perforated Panel Absorber A form of acoustically resonant absorber in which a Helmholtz resonance is created with the air mass in the perforations reacting with the compliance of the air behind the perforated panel. See Resonant Absorber, Helmholtz Resonance..
Period The time interval between identical points in a periodic signal or sound. For a sinusoid (single frequency) the period (in seconds) is calculated as 1 / frequency (in Hz). See Periodic.
Periodic In this context, a sound wave that repeats itself exactly at regular intervals. The simplest of these is a pure tone, a single frequency.
Phantom Center In stereo or surround-sound systems, a phantom center image is perceived when the same sound is radiated from left and right loudspeakers, and the listener is exactly equidistant from both loudspeakers. In multichannel systems, it may not always be possible to use a real center channel loudspeaker, in which case, a phantom center can be selected (or will occur automatically when no center loudspeaker is indicated to the surround processor during setup). A real center loudspeaker is advantageous because the sound image is heard to be in the same place by listeners in different locations. See: Center Channel, Stereophonic.
Phase For a single frequency, a periodic signal, the repetition period is divided into 360 degrees. Phase is measured as angular degrees within the period. For a single frequency, there is an equivalent time for a given phase shift, but the time for a given phase shift will be different for every frequency because the period is different for every frequency. 180-degree phase shift is equivalent to a polarity reversal. See Phase Shift.
Phase Adjustment (Subwoofers) Because they are in different locations in a room, the sound from a subwoofer and that from the satellite loudspeakers do not always combine properly, resulting in too much or too little sound in the crossover region. This is a control allowing the user to make small adjustments to the phase of the subwoofer in the hope that the situation can be improved. Sometimes it can. See: Phase, Crossover.
Phase Plug In a compression driver for a horn, this is a device conveying sound energy from the large diaphragm to the smaller throat of a horn in such a way that, over most of the operating frequency range, sound originating at all parts of the diaphragm arrive at the throat in phase. See: Horn, Compression Driver, In Phase, Throat.
Phase Response A measurement of phase as a function of frequency from the input to the output of an audio component. See Frequency Response, Transfer Function.
Phase Reversal See Polarity Inversion
Phase Shift A change in phase angle between the input and output of a device or system. This would normally be specified at several frequencies, or as a continuous curve as a function of frequency.
Phon A measure of perceived loudness originated by Fletcher and Munson. The loudness level, in phons, is the sound pressure level of a 1 kHz pure tone that is judged to be equally loud. Each of the equal-loudness contours, therefore, is identified in phons. See Equal-Loudness Contours
Phono Input/Preamplifier An input designed to accept the small voltage signals from a phonograph cartridge, to amplify them to normal line levels and to perform the inverse RIAA equalization necessary to produce properly balanced low and high frequency sounds. See: RIAA
Pincushion Distortion Geometric distortion in video pictures in which straight lines take on a concave shape, curving inward from the screen edges between the picture corners. See: Barrel Distortion
Pink Noise Random noise having a continuous spectrum and energy distributed equally on a percentage-bandwidth (e.g. octave, 1/3-octave) basis. Commonly used for audio measurements since the energy distribution is close to that of music. See: White Noise
Pitch The perceived quality of sound that is most closely related to frequency, but is also influenced by sound level. The position of a note on a musical scale.
Pixel The smallest element in a picture. An individual dot in a picture composed of dots, as in all digital video systems.
PLUGE Stands for: Picture Line-Up Generation Equipment. A test pattern used for setting the black level (brightness at the darkest part of an image) of a video display.
Polarity Being electrically positive or negative, as in the terminals of a battery or DC power supply. Being, at an instant in time, positive or negative, relative to zero voltage, in an AC signal.
Polarity Inversion In an AC signal path, to reverse the connections (as in a loudspeaker), or to invert the waveform (as in electronic circuitry). Sometimes confusingly called Phase Reversal - meaning that the instantaneous phase at all frequencies is simultaneously reversed by 180 degrees. See Phase, Out-of-Phase.
Pole Piece The cylindrical core of a loudspeaker motor, one end of which forms the inside of the magnetic gap within which the voice coil moves.
Polypropylene Thermoplastic used in speaker diaphragms. Polypropylene is weather resistant and well damped.
Port A vent or tube that forms part of a resonant system in a bass reflex loudspeaker enclosure. See Bass Reflex.
Potentiometer A resistor with an adjustable tap, used for many purposes in electronics, including the common one of volume control.
Power The amount of energy delivered or used by a device or system, expressed in Watts. In audio, power ratings of amplifiers and loudspeakers are subject to a lot of variation and uncertainty because of the very large difference in the long-term, steady-state, power rating, and the transient, or momentary, power rating, which can be several times larger. Further confusion is added when ratings at a single frequency (say, 1 kHz) are compared with the more realistic 20 - 20 kHz rating. In multichannel amplifiers, there is the further variable of ratings done with a single channel operating vs. ratings with all channels operating. The result, for consumers, is that advertised power ratings are often almost meaningless.
Power Compression In loudspeakers at high sound levels, an effect in which the acoustical output of the device increases less than the electrical input to the device. Caused mainly by the heating of the voice coil, and the consequent increase in electrical resistance. In multi-way systems, power compression affects the different drivers differently, causing the loudspeaker system to have a different spectral balance at different sound levels.
Power Handling The amount of power that may be applied to a device without causing destruction. May be expressed as "RMS" or as "continuous average" to indicate how much power can be applied for long periods. It mnay also be expressed as "peak" to indicate how much power can be applied for extremely short periods--the beat of a drum, for instance. See also Power
Power Rating See: Power.
Powered Tower A floor-standing loudspeaker with an amplified woofer or subwoofer.
Pre-amp See Preamplifier
Preamplifier An audio component that selects signal sources, and provides volume and tone compensation functions. There may be special gain stages for phono cartridge inputs. It has line-level outputs to drive a power amplifier. Normally a stereo device, its multichannel equivalent is a surround processor.
Precedence Effect In sound localization, the fact that the first arriving sound (the direct sound) normally dominates our sense of direction. This allows us to correctly identify the direction of a source of sound in a reverberant space. See: Direct Sound, Haas Effect.
Progressive Scan A video display that scans all lines sequentially in each pass. A Line Doubler can create a progressively scanned image from an interlaced scan signal. See: Line Doubler.
Progressive spider A speaker's spider that provides increasing force (to restore the cone to the resting position) as it stretches
Projector There are two ways to get an image on a screen. Shine light through an image forming element, or let light reflect from an image forming element. Both are very common. CRT projectors use an electron beam from behind and LCD devices rely on transmitted light to create the image, which is then communicated to a screen by lenses. Light valve (ILA), and D_ILA/LCOS devices rely on light reflecting off an image element, which is then focused on a screen using lenses. See: Light Valve, ILA, D-ILA, LCOS, CRT.
Psychoacoustics The branch of acoustics that relates the physical dimensions of sound with the perceived dimensions - the relationships between what we measure and what we hear.
Pulse-Code Modulation A straightforward, uncompressed, coding method in which analog signals are sampled at regular intervals and each sample is represented by a digital number representing the amplitude at that instant in time. Sampling is done at a frequency at least 2 times the highest frequency of interest, and the digital number must have a sufficient number of bits to capture and reconstruct the essential qualities of the audio signal (dynamic range, low distortion and noise, etc.). E.G. normal CD's are recorded using a sampling frequency of 44.1 kHz using a 16 bit digital number. See: Bit, Compression.
Pure Tone A single frequency having a line spectrum. The periodic waveform is that of simple harmonic motion, a sinusoid. See: Spectrum.
PVR Personal Video Recorder. A digital hard-drive video recorder (DVR) which, when combined with a program guide, can record one's personal favorite television programs. See: DVR.
Q The 'quality factor' of a resonance, related to the amount of damping or losses in the resonating system. High-Q resonances have little damping. They are very frequency specific, or narrow bandwidth, and they ring energetically. Increasing amounts of damping lower the Q, resulting in lower amplitude, wider bandwidth effects in frequency responses, and less ringing in the time responses.
Quadraphonic Four channel recodings, promoted during the late 1970's, some on tape, but mostly on matrix-encoded two-channel LP's. There was even an attempt to popularize a discrete four channel LP format using signals recorded up to about 50 kHz. It all collapsed because the industry could not agree on a single standard. Some of the clever matrix technology was incorporated in Dolby Stereo and Dolby ProLogic for movie sound tracks.
R.A.B.O.S.™ Room Adaptive Bass Optimization System (R.A.B.O.S.) utilizes a single band of parametric equalization to tame the most prominent room, mode or bass peak. These bass peaks exaggerate the sounds at their frequency resulting in bass performance that is often sloppy or boomy. By reducing the level of this peak, you are able to hear deeper, more detailed low frequencies. The sound-pressure-level meter included with the R.A.B.O.S. accessory kit allows the listener or installer to easily make the measurements required in order to properly calibrate the RABOS settings for your particular listening room.
Rarefaction A momentary pressure reduction as a sound wave passes. See: Compression, Sound Wave.
Raster The collection of horizontal lines that make up a video display. E.g. in NTSC there are 525 lines in a frame (two interlaced fields), of which 480 are visible. See: Frame, Interlaced, NTSC.
RCA Plug/Socket Radio Corporation of America, which gave its name to the very common plug and socket used for line level audio and many video interconnections.
RDS Radio Data System. RDS is digital data coded into FM transmissions which displays information such as station name, time, program information and traffic announcements alphanumerically on the receiver visual display. Obviously, an RDS compatible radio receiver is required.
Reactive Absorbers Sound Absorbers that function because of the interactions of mass, compliance and damping. E.g. Helmholtz absorbers, Diaphragmatic Absorbers. See: Helmholtz Absorbers. Diaphragmatic Absorbers, Resistive Absorbers.
Real-Time Analyzer A measuring instrument that presents spectral information, in 'real time', in the form of levels in octave or fractional/octave bands covering the audio bandwidth. Traditional instruments used 1/3-octave frequency resolution, but nowadays higher resolutions are needed, especially at low frequencies, in order to identify and correct room acoustic problems. See: Octave, Spectrum Analyzer..
Rear Projection Television A rear projector which, by using special lenses and a mirror, delivers an image to the rear of a translucent screen in a (relatively) compact enclosure. See: Rear Projector.
Rear Projector A projector that delivers a left-right reversed image to the rear surface of a translucent screen allowing the audience to view the transmitted image. See: Front Projector, RPTV.
Reflection When sound changes direction due to reflection (angle of incidence = angle of reflection) from a surface that is large compared to a wavelength.
Reflection Free Zone Location within a listening room where, for a specified interval of time following the arrival of the direct sound, reflected sounds have been attenuated by a specified amount. The purpose is to place the listener in a predominantly direct sound field for that interval of time. Used in some recording control rooms and listening rooms. Effectiveness, and need, depend on the directivity and quality of the loudspeakers, and on the 'tastes' of the listener with respect to soundstage and imaging. See: Direct Sound, Directivity, Imaging, Soundstage.
Refraction When sound changes direction as it passes through media exhibiting different speeds of sound. E.g. warm air near the ground and cooling with altitude, will cause sound waves to bend upwards. The inverse will cause sound waves to bend downwards, allowing us to hear sounds over great distances.
Resistance Electrical: The opposition to direct current flow offered by a device or material. Measured in ohms. There are also acoustical and mechanical equivalents to resistance.
Resistive Absorbers Sound absorbers, like fiberglass, drapery, upholstery, etc. that remove energy from a sound field by making it difficult for the air molecules to move in the 'fibrous tangle'. The sound energy is converted to heat. Most effective when located in regions of high particle velocity, meaning that, when placed on a surface, thick layers will be required to be effective at middle to low frequencies.
Resolution VIDEO: in digital displays, it is the number of pixels along the width and height of the picture. In any display, it is an assessment of the clarity of details in the picture. This can be different for stationary and moving objects, and the perceived resolution can be different from that which is technically defined. AUDIO: a loosely defined term used to describe perceptions of small details in music. See: Pixel
Resonance A 'natural frequency' for an acoustical, electrical or mechanical system, at which the system exhibits elevated vibration amplitude and sustained activity (ringing) after the input excitation is removed. The frequency bandwidth over which the resonant activity exists, and the duration of ringing, are related to the amount of damping in the system. This is described as the 'Q' of the resonance. See Q, Ringing, Bandwidth.
Resonant Absorbers Sound absorbers that are mechanically resonant (e.g. diaphragmatic absorbers) or acoustically resonant (Helmholtz absorbers), being most effective at and around their tuned frequencies.
Reverberation In a room, it is the sound that has been reflected many times from many objects and surfaces. In large rooms and concert halls the reverberation can last long enough to be heard as a gradual decaying of sound after the source has stopped radiating. So called 'live' rooms have a lot of reverberation. 'Dead' rooms have little.
Reverberation Time The time it takes for reverberation to decay by 60 dB (roughly, to inaudibility) after the sound source has ceased. See: Sabine.
RF Audio/Video An antenna or cable-like connection provided to allow audio and video signals to be communicated to TV's which have only this kind of input. Many VCR's and cable boxes provide these RF (audio and video are modulated on a VHF carrier) outputs. Technically, it is the worst form of connection. Use only when absolutely necessary.
RF remote A remote control that communicates by means of radio frequency (RF) waves. These can travel through walls, and other objects, like a cordless telephone, thus making them very useful in a home. See: IR remote.
RGB RGB = Red, Green, and Blue the three 'primary' colors which, in different combinations, can form all other colors. Also the three connectors and cables that can be used to communicate picture information in this format.
RIAA Recording Industry Association of America. Also, the name of the standardized equalization curvess used in making and playing back LP recordings.
Ringing The natural tendency of an activated resonant system remain active after the excitation is removed, decaying gradually over time. The decay time decreases with increasing damping. See Resonance, Q, Tinnitus.
RMS See Root Mean Square.
Roll-off The attenuation of frequencies above or below a certain point.
Room Acoustics The collection of physical properties in a room that collectively give it a recognizable character when listening to live or reproduced sounds.
Room Proportions The ratio of length to width to height of a room. Significant because this ratio determines the distribution, in the frequency domain, of all of the acoustical resonances in a simple rectangular room. Large openings and non-parallel surfaces upset the relationship.
Room Resonances Acoustical resonances in rooms that occur between opposite parallel surfaces (axial modes), among four surfaces, avoiding a pair of opposing parallel surfaces, e.g. the four walls, or two walls and the floor and ceiling (tangential modes), and among all surfaces (oblique modes). See Standing Waves.
Root Mean Square Electrical: the square root of the time average of the squared (voltage or current) over one cycle of a periodic signal. Also called the 'effective value', it is used to calculate power in AC signals. Thus, the RMS power rating of a power amplifier is calculated using the RMS values of voltage and current, and represents its ability to produce continuous power, as opposed to momentary or peak power.
RPTV See: Rear-Projection Television
RT60 See: Reverberation Time.
RTA See: Real-Time Analyzer.
Sabin A unit of measure for sound absorption. 1 Sabin = the absorption of one square foot of a surface having 100% absorption e.g. an open window). See: Absorption Coefficient, Sabine.
Sabine Wallace Clement Sabine, a founder of modern architectural acoustics (1868-1919). Developed a relationship between reverberation time and the amount of acoustical absorption in a room. Designed Boston Symphony Hall, considered to be one of the best concert halls in the world. See: Reverberation Time, Sabin, Absorption.
Satellite Loudspeaker A loudspeaker designed to function with a subwoofer, and therefore it has limited low-frequency output. At higher crossover frequencies, the satellites can be very small, the size of a coffee cup, but maximum loudness is limited and the risk of localizing the subwoofer increases. At lower crossover frequencies, say 80 Hz (a common high-quality standard), satellites need to be "bookshelf" size or larger, but the whole system has more dynamic range and potentially higher sound quality. See: Subwoofer, Crossover, Localization, Dynamic Range.
Saturation The extent to which a pure color has been diluted with white. Highly saturated colors have little white in them. Lower levels of saturation look washed out with the white content.
Scan Line One horizontal line in the raster of a video display. See: Raster.
Scan Rate The frequency with which a video display reproduces scan lines. Standard NTSC television has a scan rate of 15,734 lines per second (525 lines per frame multiplied by 29.97 frames per second).
SDARS SDARS (Satellite Digital Audio Radio Services) is an umbrella term for satellite-supported radio systems in North America. There are currently two different systems: Sirius Satellite Radio and XM Radio.
Sealed Enclosure See Acoustic Suspension
SECAM The French original, SEquential Couleur Avec Memoire means SEquential Color with Memory. A television broadcast standard used in France, several European/Mediterranean and African countries, and others. 625 lines displayed at 50 fields/second. Of these, about 576 lines contain picture information. See: PAL, NTSC, Television Systems.
Sensitivity A standardized measure of the sound output of a loudspeaker for a known input signal. Originally, the input power was 1 watt. Nowadays, the input is standardized to 2.83 volts (1 watt into 8 ohms). Measurements are made on axis in an anechoic space, at a distance that places the microphone in the far-field of the loudspeaker system, and then the sound pressure level is calculated for a microphone distance of 1 meter. A measurement distance of 1 meter is too close for all but single drivers and very small loudspeaker systems. See also: Far Field, Input Sensitivity.
Separation A measure of the independence of the channels in a multichannel system. It tells us how much unwanted signal leaks into any of the channels. In practice, from the point of view of maintaining good sound image localization, 20 dB or more channel separation is required.
Series Connection A circuit where components are wired sequentially, in head-to-tail fashion, across a pair of terminals. The terminal voltage is then divided between them in proportion to their impedance characteristics. Each of two identical loudspeakers would receive half of the voltage, and half of the power, delivered to the series combination. This connection is often used in A/V receivers in A, B, A+B loudspeaker switching, to prevent confronting the power amplifiers with loads they cannot drive. The tradeoff is reduced maximum power to each loudspeaker. See Parallel Connection.
Series-Parallel Connection A circuit where there are components wired in series and also in parallel to get the desired result out of the combination. This is often used in multi-loudspeaker systems to optimize the impedance seen by an amplifier.
Servo Control Subwoofer A powered subwoofer that uses feedback from the motion of the voice coil to control the power provided to the speaker by the amplifier.
Set-Top Box A device, including a tuner, for receiving terrestrial, cable or satellite signals and feeding them to the television display. Set-top boxes may include other features, like games, storage, web access, etc. See: Tuner, Terrestrial.
Shielded Loudspeaker A loudspeaker in which the stray magnetic field has been minimized so that it can be located near a CRT video display without distorting the picture.
Short Circuit A direct connection, usually accidental, between the positive and negative portions or terminals of a circuit, bypassing some or all of the components of the circuit and preventing operation. Connecting both leads of a loudspeaker wire together presents the power amplifier with a short circuit, causing it deliver far more current than it was designed to. With luck it will sense the danger and protectively shut down. If not it will lapse into an expensive silence.
Simultaneous Masking Masking that occurs when a loud sound prevents us from hearing other, smaller, sounds that occur simultaneously. See Masking, Threshold Shift.
Sine Wave See: Pure Tone.
Sinusoid See: Pure Tone.
Slat Absorber An acoustically resonant absorber in which the air mass in the spaces between the slats reacts with the compliance of the air behind the slats to form a Helmholtz resonator. See: Resonant Absorber, Helmholtz Resonance.
SLM See Sound Level Meter.
Sone The unit of perceived loudness. One sone is the loudness of a 1000 Hz tone at a sound pressure level of 40 dB. Two sones would be twice as loud and, at middle and high frequencies, that would require an increase in sound level of about 10 dB. At low frequencies it would require less. See: Loudness, Equal-Loudness Contours, Sound Pressure Level.
Sound There are two definitions. Physically, sound consists of pressure fluctuations, at any frequency, that propagate in an elastic medium, such as air. Perceptually, sound is the human response to those physical pressure fluctuations, which are normally considered to occur in the frequency range 20 Hz to 20 kHz.
Sound Absorption Coefficient See: Absorption Coefficient.
Sound Intensity A measure of the sound energy propagated in a specific direction. Measured as watts/square meter over an area normal to the direction of propagation. The term is often incorrectly used when sound level, or sound pressure level is really intended.
Sound Level Sound pressure in decibels, usually referenced to the standard level near the hearing threshold at middle frequencies, and almost always weighted according to one of the standard frequency weighting contours, A, B or C. Such sound levels should be described as dB (A), for example. See Frequency Weighting.
Sound Level Meter A meter that measures sound pressure levels, with or without frequency weighting, and with the option of fast or slow averaging times. See Frequency Weighting.
Sound Power A measurement of the total sound radiated from a loudspeaker without regard to direction. Ideally measured at many points on an imaginary sphere surrounding the loudspeaker. One of several factors used in predicting how a loudspeaker may sound in a room.
Sound Pressure Level A measurement in which the sound pressure is expressed as so many decibels (dB) above a standard reference pressure level, which is close to the threshold of hearing at middle frequencies. SPL, as it is called, is a standardized measurement, and is always done with the measuring instrument set to the "linear" mode, with all frequencies represented equally. Measurements made with A, B, C, or other weightings, are called Sound Level measurements. See Frequency Weighting, Hearing Threshold, Sound Level.
Sound Ray A graphic way of illustrating the direction in which sound is propagating. It is commonly used to illustrate how sound reflects in rooms (angle of incidence equals angle of reflection) where it works well at frequencies where the wavelengths are small compared to the dimensions of the reflecting surfaces.
Sound Transmission Class A rating number used to classify the sound attenuation capabilities of various walls, floors, ceiling, doors, windows, etc. It is measured over the frequency range 125 - 4000 Hz, as it is intended to evaluate speech privacy, and so it tells us absolutely nothing about isolating the bass frequencies - one of the most serious problems with home entertainment systems. Abbreviated: STC, and it is specified in dB, larger numbers being better.
Sound Wave A pressure fluctuation that propagates in air, or any other elastic medium. See: Compression, Rarefaction.
Soundstage A general term embracing the perceived dimensions of direction and space pertaining to musicians performing in an acoustic space. Usually used in discussions of stereo and multichannel reproduction of recordings. Dimensions like width, depth, 'air' or space, and the directional clarity and size of individual performers are matters of interest. See: Ambience, Localization.
Spaciousness An important property of concert halls, in which reflections from side walls (lateral reflections) generate a desirable sensation of space. One of the reasons for multichannel reproduction in homes and in cars, where the objective may be to recreate these impressions.
Spatial An attribute of an audio system's playback that creates a sense of space within or different from the listening space
Speaker see Loudspeaker
Speaker Level The signal that comes out of a power amplifer, intended to drive a loudspeaker. Sometimes speaker level signals are used to provide input to an amplified subwoofer from a receiver having no line level subwoofer output. See: Line Level
Spectrum The distribution of energy in a signal or sound, displayed as amplitude as a function of frequency. Strictly, it is the result of a spectrum analysis on a signal, but it is loosely used to describe certain applications of frequency response data. Periodic signals tend to have spectra in which the energy is concentrated in one or more lines (a line spectrum). Discontinuous or random signals may have continuous spectra. See: Frequency Response, Spectrum, Spectrum Analyzer.
Spectrum Analyzer A measuring instrument capable of displaying the distribution of energy in a signal or sound. With contemporary techniques, frequency resolution can be almost whatever one wants, from 1 Hz (or many other fixed-bandwith options) to a variety of percentage-bandwidth options, such as fractional-octave displays. Most employ FFT methods, and some can display results in 'real time', others not. See: FFT, Real-Time Analyzer.
Speed of Sound In air, at 72 degrees F (22 degrees C), it is 1131 feet/second, or 345 meters/second. All audio frequencies travel at the same speed. In denser, stiffer materials, sound travels at higher speeds.
Spider The part of the speaker attached to the junction of the diaphragm and voice coil that keeps the voice coil aligned in the gap and helps to suspend the cone.
SPL See Sound Pressure Level.
SSP™ Networks Straight-Line Signal Path™ Networks
Standing Waves Associated with room resonances, at low frequencies, these can result in large variations in sound level at different frequencies at different locations in the room. The bass sounds different as one moves around a room. See Resonance.
Starfish Tweeter Mounting System A tweeter mounting system included in car audio component speaker systems that includes a mounting cup with several break-off mounting tabs. The system facilitates mounting in factory tweeter locations.
STC See Sound Transmission Class
Stereophonic Literally, solid sound. In theory, stereophonic systems could have any number of channels, but now the term is used to describe systems having two-channels. Stereo is designed for a single listener located equidistant from the left and right loudspeakers. Moving to the side, away from this location, causes the stereo image (soundstage) to collapse towards the nearer loudspeaker. See: Phantom Center.
Straight-Line Signal Path™ SSP (STRAIGHT-LINE SIGNAL PATH™) NETWORKS • This crossover design provides the shortest route from the input terminals to the transducers. • Minimizes signal loss and noise. Benefit: Ensures that a strong, precise signal arrives at each driver.
Subwoofer A loudspeaker system especially designed to reproduce only bass frequencies. Generally used only below 80-100 Hz.
Superposition An important property of sound fields in which, what happens at a point in space is the vector sum of all separate events. It means that one can analyze individual components, e.g. direct and reflected sounds, and then mathematically add them together to determine the final result, exactly as happens in the physical world.
Supraaural Headphones Headphones that sit directly on the ears. See: circumaural headphones, in-ear headphones.
Surround In loudspeaker drivers: the flexible support surrounding a loudspeaker diaphragm in the rigid frame, usually a half roll or corrugated shape. In audio systems: describing any of several ways to provide multichannel sound that surrounds the listeners with sound.
Surround Processor An audio component that selects signal sources, provides volume and tone compensation functions, and decodes and/or provides setup and calibration functions for several multichannel surround-sound modes.
Surround Sound A generic term that describes any of several systems capable of delivering multichannel audio that includes channels placed to the sides and/or rear of the listener.
Surround Sound 5.1 A multichannel sound system, with five main channels and a low-frequency effects (LFE) subwoofer channel. Surround sound was developed from cinema technology. All six channels are discrete, meaning they are stored and played back separately.
Surround Speaker A speaker typically matched in size to the midrange speakers used in a system. Its primary function is to “carry” sound throughout the listening area so that the listener feels enveloped in sound. The size and material of a surround speaker should closely match the midrange speakers in the system; this ensures that the “moving” sound doesn’t waver, or change timbre, thereby guaranteeing a rich, full-range surround-sound experience.
Suspension In a loudspeaker: the compliant surround and spider that support the diaphragm while allowing it to move freely in and out. See Spider, Surround
SVGA Super Video Graphics Array. A computer display with 800 x 600 pixel image resolution. See: Pixel, VGA, XGA, SXGA.
S-VHS A VHS format video cassette recorder that can record and play back s-video signals. See: S-Video
S-Video A video signal in which the chrominance (C) and luminance (Y) signals are kept separate. They are stored separately on S-VHS and DVD media, and using this output means that the two components do not need to be combined by the player and then separated by a comb filter in the video display. If the source, e.g. laserdisc, stores a composite signal (Y & C combined) then the decision to use the s-video connection is based on whether the comb filter in the player is better than the comb filter in the TV. See: Chrominance, Luminance, Composite, Comb Filter.
SXGA Super Extended Graphics Array. A computer display with 1280 x 1024 pixel image resolution. See: Pixel, VGA, XGA, SXGA.
Symmetrical Field Geometry A speaker motor assembly design intended to maintain uniform magnetic force throughout the travel of the voice coil. The objective is to reduce distortion at large diaphragm excursions.
Tangential Modes See Room Resonances.
TDS See: Time Delay Spectrometry.
Television Systems Three incompatible systems exist in the world. NTSC has 525 lines, presented at 60 fields/second (about 480 picture lines), while both PAL and SECAM have 625 lines presented at 50 fields/second (about 576 picture lines). All of these are used for broadcast, cable and satellite transmission, as well as for DVD-video. See: NTSC, PAL, SECAM, Field, Raster, Scan Lines.
Temporal Masking Masking that occurs when a loud transient sound prevents us from hearing sounds that occur just earlier (backward masking) and just later (forward masking) in time. See Masking, Threshold Shift.
Terrestrial Jargon for radio and television signals that propagate normally from a transmitter on the ground (terrestrial) to a conventional antenna. Also called over the air (OTA).
Three-Way Loudspeaker See: Loudspeaker System.
Threshold of Pain When sound levels are sufficiently high as to cause discomfort, or pain, in the ears of listeners. Very approximately, 110+ dB, as it varies with individual listeners and with the kind of sound.
Threshold Shift A change, normally an elevation, in the hearing threshold. It can be permanent, as in hearing loss, or temporary, as occurs when the audibility of some sounds is reduced by the presence of others, in masking. See Masking, Hearing Loss.
Throat In a horn loudspeaker, this is the smallest part, where the sound leaves the driver begins its travel down the expanding flare of the horn itself. See: Horn, Compression Driver, Phase Plug.
THX THX was created by George Lucas to apply performance standards to cinema sound systems ensuring the playback quality of film sound tracks. Named after his first feature film, THX 1138. Expanded into home audio, and other areas. THX is now a private licensing company issuing certifications, paid for by manufacturers, that products meet certain performance standards, and incorporate certain functions, some of which are proprietary. There are levels of certification, from very basic to high. It is a reassurance to customers, but it needs to be noted that non-THX-certified products can also offer performance that is as good or better.
Timbre The essential distinctive perceived quality of a sound, separate from loudness and pitch. That which allows us to recognize whether the same note has been played by a piano or a guitar, a clarinet or a trumpet, or sung by Pavarotti or Sinatra.
Time-Delay Spectrometry A measurement system that allows one to examine events in time as well as frequency, and to isolate a direct sound from later reflected sounds in a normal room, thus approximating anechoic measurements. There are trade-off's though. As the measurement time window is shortened, e.g. to eliminate later reflections, the frequency resolution of the measurement is reduced. An anechoic measurement space is still desirable. See: Anechoic, Direct Sound.
Tinnitus A ringing in the ears that accompanies temporary hearing loss after exposure to loud sounds, or that becomes permanent for some individuals unfortunate enough to incur permanent hearing loss.
Tone Burst A time sample of a single frequency (pure tone) which contains some number of complete cycles. The burst may be turned on gradually or abruptly, all of which affects the spectrum of the signal and how it sounds. Once a pure tone is interrupted, it no longer has a single frequency spectrum.
Tone Control A simple filter that can boost or cut portions of the Frequency Range','Glossary',775,400,'right')" class="link">audio frequency range, used to change the tonal balance of reproduced sound. See Bass Control, Treble Control, Equalizer.
Transducer A device that converts energy from one form to another. For example, a microphone converts acoustical energy into electrical energy, while a loudspeaker does the reverse.
Transfer Function An input-to-output measurement of performance that includes both amplitude and phase as functions of frequency. The Fourier transform of the transfer function is the impulse (time) response of the system. See: Frequency Response, Phase Response, Fourier Transform, FFT.
Transform A computational procedure or set of rules by which a signal can be converted from one form into another. See Fourier Transform
Transformer An electronic component consisting of two or more coils of wire in close proximity, allowing the transfer of energy from one to the other by means of inductive coupling. Many applications, including electrical isolation, voltage transformation, impedance matching, etc.
Transient Response A measure of the time domain response of a system, input-to-output, to a very brief transient signal at its input. It is widely believed that the time-domain behavior of a device is independent of the frequency response. However, the Fourier transform of this time-domain waveform is the frequency-domain transfer function. See: Impulse Response, Transfer Function, Fourier Transform, FFT.
Transparency The objective of every maker of windows, and conscientious loudspeaker manufacturers, who attempt to provide a transparent - i.e. unmodified - rendering of an audio work of art.
Treble High-frequency audio signals
Treble Control A tone control allowing the user to boost or cut the high frequency portion of the audio signal.
Tuned Port Bass Enclosure See Bass Reflex
Tuner A device that tunes, or selects, radio or television stations from broadcast signals received on a terrestrial antenna, by cable or satellite.
Tweeter A loudspeaker driver optimized to reproduce high frequencies, typically above about 2kHz to 4kHz.
Two-Way Loudspeaker See: Loudspeaker System.
Ultrasound Sound waves with frequencies higher than those that are normally audible by humans. Typically, sounds above about 20 kHz.
Unbalanced Connection An interconnection between audio components in which there are two conductors, signal and ground. The 'unbalanced' aspect of this connection is that, since ground is the reference, each of the two signal leads has a very different (unbalanced) impedance relationship to to the reference. This is of no consequence unless there are noises or hum potentials in the grounding of the interconnected components. Commonly employs a coaxial cable, in which the outer cylindrical shield serves as the ground connection. If hum problems are found, it is possible to selectively break the ground connection, and thus break the ground loop. See: Balanced Connection, Coaxial, Ground, Ground Loop.
Unipivot Tweeter A tweeter, mounted at an angle atop a midrange speaker's polepiece that can be rotated so that it points at the listening position.
Upmixing The process of converting a program created in one format so that it can be played in another that uses more channels. This is often done in recording studios under the guidance of a sound engineer and/or musicians. If it is done by a fixed algorithm or process, it is sometimes called "blind" upmixing.
UXGA Ultra Extended Graphics Array. A computer display with up to 1600 x 1200 pixel image resolution. See: Pixel, VGA, XGA, SVGA, SXGA.
VCR Video Cassette Recorder
Vent See Port.
VGA Video Graphics Array. The basic computer display standard, having 640 x 480 pixel image resolution. See: Pixel, XGA, SVGA,SXGA.
VHS VHS = Video Home System. An analog video cassette recording (VCR) system developed by Matsushita (Panasonic, JVC) in 1976.
VHS-C Developed for video cameras, it is a physically small tape cassette, in the VHS format, which can record up to about 30 minutes. With an adapter it can be played on any VHS machine. See: VHS
VHS-C Developed for video cameras, it is a physically small tape cassette, in the VHS format, which can record up to about 30 minutes. With an adapter it can be played on any VHS machine. See: VHS
Video Shielded See Shielded Loudspeaker
VMAx® VMAx® creates a three-dimensional sound field using only conventional left and right front speakers. The result is sound that fills a room and puts you at front row, center.
Voice Coil A coil of wire attached to the rear of the speaker diaphragm. When a current is passed through the voice coil there is an inductive interaction with the stationary magnetic field generated by the magnet, causing the diaphragm to move. This is the basis of the loudspeaker motor. See Magnet, Motor.
Volt See Voltage
Voltage Electrical potential difference measured in volts.
Volume Audio: loosely, the loudness of sound, and the control that allows us to vary it. Loudspeakers: The cubic measure of space in a speaker enclosure.
VOM Volt, Ohm, Milliammeter. An analog meter that measures voltage, resistance and current.
Watt The basic unit for electrical or acoustical power. See: Power
Wattage Amount of electrical power expressed in watts. See: Power.
Wave See Sound Wave
Waveform The amplitude of a sound or electrical wave displayed as a function of time. The 'shape' of a wave
Wavelength The distance traveled by a single-frequency sound as it propagates. In air, it can be calculated by dividing the speed of sound (1130 ft/s, 345 m/s) by the frequency.
W-dome tweeter A tweeter that includes a voice coil that is substantially smaller in diameter than the tweeter's diaphragm. W-dome tweeters often look like little cones with the voice coil former attached to the inner diameter.
White Noise Random Noise having a continuous spectrum and constant energy per cycle. Compared to pink noise, white noise sound bright. See: Pink Noise
Widescreen A video display that is wider than the standard 4:3 aspect ratio although, in the context of DVD and HDTV, widescreen refers specifically to a 16:9 aspect ratio. See: Aspect Ratio.
Woofer A loudspeaker driver designed to reproduce bass frequencies.
XGA Extended Graphics Array. A computer display with either 640 x 480 or 1024 x 768 pixel image resolution. See: Pixel, VGA, SVGA, SXGA.
XLR A professional grade three-pin connector conveying balanced line level audio signals between components. See: Balanced Connection, Unbalanced Connection.
Y-adapter A signal connecting cable designed to provide signal to two devices rather than one. It looks like the letter "Y", hence its name