Audio  - Home Theater FAQ's and Information

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Audio Glossary and Terms A Thru F

A

Acoustic / Acoustical - Having to do with sound that can be heard by the ears.

Acoustical Absorption - The quality of a surface or substance to take in the soundwave and not reflect it or pass it through, or an instance of this.

Acoustic suspension speaker - A type of speaker system in which the air in the enclosure acts as a spring that shapes the response of the driver/box system, and also works as the dominant restoring force on the driver cone.  Acoustic suspension designs have lower sensitivity than ported designs (see below) and therefore need additional amplifier power to achieve the same sound pressure level as an otherwise equivalent ported box. Acoustic suspension designs, though, are able to play lower in the frequency spectrum at the same volume, and provide tighter and better-defined sound.  Not all sealed speakers are acoustic suspension designs.

A/D - An abbreviation of analog to digital conversion (the conversion of a quantity that has continuous changes into numbers that approximate those changes), or Analog to Digital Converter.

AES - An abbreviation of Audio Engineering Society.

AES/EBU Professional Interface - A standard for sending and receiving digital audio adopted by the Audio Engineering Society and the European Broadcast Union.

Ambient Field - A term with the same meaning as the termreverberant field (the area away from the sound source where the reverberation is louder than the direct sound.

Amp - 1) An abbreviation of the term amplifier (A device which increases the level of an electrical signal. 2) An abbreviation of Ampere (the unit of current). 3) An abbreviation of amplitude (the height of a waveform above or below the zero line).

Ampere - The unit of current, abbreviated Amp.

Amperage (Amperes, Amps, symbol A or I) - units of measurement of electrical current.  Current is the flow of electrical charge carriers, usually electrons, through an electronic circuit. Using the analogy of water flowing through a pipe, current is the equivalent of the flow of water moving through it.

B

Bandwidth - When applied to parts of the frequency spectrum, bandwidth is the range of difference between the highest and lowest frequencies contained in a signal. Audio bandwidth is typically listed as 20 Hz to 20 kHz, or cycles per second.

When applied to audio equipment, bandwidth indicates the range over which it will reproduce audio frequencies without attenuation.  The bandwidth of some commonly used media that operate in or near the audible range:

In telecommunications, the term bandwidth indicates capacity of a communications channel.  Analog communications bandwidth is measured in cycles per second, or Hertz (Hz); digital communications, in kilobytes per second (kbs) of data transfer.  Analog telephone channels may have a bandwidth of 4,000 Hz, while a digitally encoded telephone channels might offer a bandwidth of 64 kbs.

Bass reflex speaker - a type of vented speaker enclosure in which the mass and spring characteristics of air in the vent (or port) help determine the low frequency response of the driver/box system.  Above a certain frequency, determined by driver characteristics and the length of the port, the driver and the air in the port work in phase to produce a sound pressure level higher than that of a similarly sized sealed enclosure.  Below that frequency, the port and the driver work against each other, out of phase, so output decreases rapidly. The resonant characteristics of port and driver combine to produce a different sound quality different than that of a sealed system.

Biamp - A technique that uses two amplifiers to drive one loudspeaker. One amplifier powers the midrange/tweeter section; the other powers the woofer.  An active crossover placed between the preamp and power amps selects the high and low frequencies to send to their respective amplifiers.  This setup is particularly useful when different levels are required for the woofer and midrange/tweeter.  A speaker must have two sets of connecting terminals to use this method.

Bipole - A speaker which radiates sound primarily in opposite directions, yet in phase, so as to diffuse the soundstage and offer a sense of width. Bipole speakers are almost always designed with two drivers, wired in phase, on opposite faces of a cabinet.

Biwire - A wiring technique that employs two runs of wire from amplifier output terminals to speaker: one for the woofers; another for the midrange/tweeter drivers. The speaker must have two separate sets of terminals to use this wiring method.  Compared to biamping, biwiring tends to be subtle in sonic difference, requiring listening sophistication to discern any qualitative change.

Boost - To increase gain, especially to increase gain at specific frequencies with an equalizer.

C

Classes of Amplifiers - Amplifier classifications describe the methods by which they amplify signals.  The most common classes are Class A, Class B, and Class AB.

Class A amplifiers keep output stages on at all times, which minimizes distortion but uses significant amounts of power. 

Class B amplifiers keep output stages off until a signal appears.  This cuts power use dramatically, but introduces distortion during the stages turn-on phases.

Class AB amplifiers use a positive/negative device to shut off its outputs nearly entirely, except for running a small bias current, when not needed.  It does this by almost completely turning off positive polarity output off during negative signal cycles, and negative output stages off when the signal is positive.

These amplifiers provide a compromise between the sound quality of class A and the efficiency of class B, offering lower distortion than the latter and less power and heat loss than the former. This is the reason that the majority of audio amplifiers are class AB. 

Class G amplifiers use the basic class AB design, but add other devices to control power use.  They do this by one of two methods. One is to connect a single class AB output stage to two power supply rails by a diode or transistor switch which only connects the lower supply voltage unless large signal peaks occur, at which point it switches to the higher rails.  The other approach uses two class AB output stages, each connected to a different power supply voltage, with the magnitude of the input signal determining the signal path. Either approach improves efficiency enough to yield significantly more power for a given size and weight, or less size and weight for a given amount of power. 

Clipping (in amplifiers) - A distortion of the audio signal that occurs when an amplifier reaches the limit of its power output and attempts to increase the output level further by roughly clipping off the tops and bottoms of waveforms.  The sound of clipped waveforms is hard and edgy, and have a much higher percentage of high frequency energy than unclipped signals. This energy, being significantly high frequency, gets routed straight to the tweeters, which have very small voice coils that can't handle as much power as a larger woofer voice coil, and can thus be easily burned out by clipped signals.  Since lack of sufficient amplifier power to drive signals causes clipping, you are more likely to damage a tweeter with a lower power amplifier than a higher power amplifier. 

Coax - Two-conductor cable consisting of one conductor surrounded by a shield.

Compression - a method of treating information in such a way as to reduce its total output.  In analog audio, compression means squashing down the peaks in audio output signals.  In digital audio, compression means encoding digital information to reduce the total size of the data stream by eliminating information considered to be redundant, unnecessary or at least not critical.

D

Decibel (dB) - The unit by which amplitude is measured.  Decibel measurements occur along a logarithmic scale in which each 10 dB increase represents a tenfold increase in signal amplitude, while each 10 dB reduction represents a tenfold reduction. The original unit of measurement was the Bel, a ten times larger measurement (ie, one Bel = ten dB). As electronic equipment improved, however, its one-tenth-size relative, the decibel, came to be the standard unit. The dB scale is useful in measuring changes in systems which our nervous systems perceive in logarithmic ways, such as sound. The most common use of the decibel is in measuring sound pressure level.

Dip - To reduce the level of signals in a specific band of audio frequencies.

Dipole - A speaker which radiates sound primarily in opposite directions, 180 degrees out of phase,  This creates a null, or area with no sound, to the sides of the speaker. Such designs are engineered by using drivers wired out of phase, or by using both sides of a flat driver.

Dipole speakers are most commonly used as surround channel speakers IN older multi-channel systems. They create a spacious sound field that makes it difficult to tell the exact location of sound sources, which is useful in creating the effect of being in a larger space.

Discrete  - Separate, with no predetermined interaction between elements. In electronics, the term refers to a design that uses individual parts rather than an integrated circuit. In audio equipment, it means a system made up of separate, single-function components rather than combination equipment.  And In multi-channel audio systems,  it indicates a system in which the signals on individual channels are uniquely different from each other.

Dolby - The name of a manufacturer (and a trademark) of noise reduction systems and other audio systems, to improve performance and fidelity of audio recording, playback, and transmission.

Dome Tweeter - A small, protruding hemi-spherical driver which reproduces high frequencies.  Speakers using dome tweeters offer wider high-end dispersion and smooth frequency response.

Doppler Effect - A change in frequency of a delayed signal caused by the delay time changing while the cycle is being formed.

Driver (Subwoofer, Woofer, Midrange, Tweeter) - The individual component of a loudspeaker system that converts electrical energy into sound energy. Tweeters, midranges, woofers, and subwoofers are all examples of drivers, and all are technically known as transducers; ie, devices which transform one type of energy into another.  All are made up of a linear magnetic motor and a piston; the piston, in this case, being the part that drives air -- in most cases, a cone or dome.

The Woofer, named for the low tones that it reproduces, is used for low frequency reproduction. It's usually the largest driver on a speaker, has the widest surround mounting, and creates long bass wavelengths by displacing large volumes of air.  At the lowest frequencies, its movement is often dramatically visible.  Subwoofers are woofers placed in separate cabinets for the sake of driver size (when all other factors are equal, larger equals extended lower range) and placement flexibility.

The Midrange driver, used for mid frequency reproduction in three-way speakers, tends to be smaller than the woofer, and a bit thinner in material so that it has the flexibility to reproduce higher frequencies.

The Tweeter, which handles the high frequency reproduction, is the smallest of a speakers drivers, and is made of the thinnest and most delicate material so that it can respond the most quickly.  It is usually a small cone or dome; in rare cases, it takes the form of a ribbon.

Dry - 1) Having no reverberation or ambience. 2) More loosely used to describe an audio signal without any signal processing.

DSP - An abbreviation for Digital Signal Processing (Any signal processing done after an analog audio signal has been convened into digital audio).

DVD Audio - A DVD formatted disc that contains between two and six high quality channels of audio material.  DVD-A, as it's known, doesn't use data compression (unlike like Dolby Digital and DTS, both of which do) that could result in loss of signal detail. To play back most DVD Audio discs, a player capable of playing this format; ie, displaying the DVD Audio logo, is required.  Some DVD-A discs, though, also contain DTS or Dolby Digital tracks, and can be played on any DVD player.  The DVD-A format, however, offers a 24 bit wordlength and 96 Kb clock rate, which makes its resolution the highest of any common digital audio format.

Dynamics -  The amount of fluctuation in level of an audio signal

Dynamic Range -The difference between the loudest and the softest sounds either contained in a piece of musical or other audio material.  In reproducing audio material, it means the range that can be reproduced by a piece of audio equipment or audio format without distortion. This ratio is expressed in dB.

Typical dynamic range for audio media:
Cassette  65 dB
CD          96 dB
SACD      120 dB
DVD Audio 144 dB

E

Equipment Rack - A cabinet with rails (or free standing rails) that have holes to accept screws at standard spaces and used to house outboard gear.

F

Frequency (Hz) - Rate of recurrence of oscillation, measured in cycles per second (cps), and expressed in units known as Hertz (Hz).  A 1 Hz frequency is a signal that completes one entire cycle of oscillation in one second; a 100 Hz frequency completes a hundred.  With cycles exceeding 1000 a second, we instead use the unit kilohertz, or kHz; a 15,000 cycle-per-second tone is referred to as 15 kHz. Human sense of pitch is related to frequency; usually we hear frequencies with few cycles per second as low, and those more as higher. We also hear frequencies in simple arithmetical relation to each other as pleasant.  For instance, all known human musical scales begin to repeat at the point of the octave, whose upper and lower tones differ in Hz by exactly 2:1.

In pure engineering terms, separate from where engineers and designers might set the crossover points in speaker systems, we divide the frequency range into three categories:  low, mid and high.

Low Frequency is usually defined as the range from 20 to 100 Hz.  Because they cycle slowly, relative to mid and high frequencies, they have longer wavelengths in air. These long length waveforms easily diffract around smaller objects, making their way around any barriers of less size.  We tend to perceive low frequencies as omni directional.

Mid Frequency is usually held to occupy the range from 100 to 2,000 Hz.  This is the range in which most basic instrumental and vocal tones occur and in which human hearing is the most sensitive.  Mid frequency sounds and tones, with shorter wavelengths, are more easily absorbed by medium sized obstacles, and less likely to be clearly discernible around corners or through barriers.

High Frequency is usually considered to be in the range from 2,000 to 20,000 Hz.  These frequencies, which often arise from smaller sources -- a constricted throat, a small finger cymbal, the tiny contact point between a fingernail and a chalkboard -- are also best reproduced by small speakers.  Their rapid cycle time gives them very short wavelengths which are easily absorbed by objects -- such as carpet or furniture -- whose thickness is greater than their own cycle lengths.  For this reason, they usually cannot make their ways around obstacles or corners unless strongly reflected by hard surfaces.  They are, ultimately, the most fragile of the frequencies -- easy to lose in recording and mixing, and requiring quality components and placement care to accurately reproduce.

Human hearing, which perceives all three of these ranges, is commonly held to range from 20 Hz to 20,000 Hz, although a few of us can hear higher or lower, and most of us have less than that full range by adulthood.

Frequency Range - The cycles-per-second span over which any object can naturally emit a sound is also known as the objects frequency range. Some examples of fundamental frequency range for common voices and instruments:

Soprano Voice:    ~300 Hz-1000 Hz
Tenor Voice:  ~150 Hz-500 Hz
Bass Voice:  ~90 Hz-300 Hz
Piano:   ~30 Hz-4 kHz
Pipe Organ:  ~17 Hz-8 kHz
Guitar:   ~75 Hz-700 Hz
Trumpet:   ~180 Hz-900 Hz

Frequency Cutoff - The frequency above or below which audio equipment ceases to function with full efficiency, either due to inherent limitation or deliberate design. Typically, cutoff frequency specifications are assigned to the point at which response drops by 3 dB relative to full output, and continues to fall the further one measures in that direction.

Full - A quality of the sound of having all frequencies present, especially the low frequencies.

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Salem, OR 97303

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