This glossary is meant to give you a basic understanding of audio terms. Think of it as a Soundman-To-English dictionary. By reading these terms you will gradually expand your knowledge and sometimes even understand things that were once only understood by eccentric and confusing live sound and recording engineers or Alto product designers.

Acoustic feedback - A squealing sound when the audio output of a P.A. system is picked up by a microphone and sent, in phase, back into the mixer’s input.

Acoustic suspension - A sealed or closed box speaker enclosure. Also called a sealed enclosure, or infinite baffle.

Ampere (A) - The unit of measurement for electrical current in coulombs per second. There is one ampere in a circuit that has one ohm resistance when one volt is applied to the circuit. See Ohms Law.

Amplifier - An electrical circuit designed to increase the current, voltage, or power of an applied signal.

Amplitude - The relative strength (usually voltage) of a signal.

Attenuation - The reduction, typically by some controlled amount, of an electrical or acoustic signal.

Audio frequency - The acoustic spectrum of human hearing, generally regarded to be between 20 Hz and 20 kHz.

Audiophile signal processing (Analog) - Really expensive esoteric rackmount effects processors designed to reduce tape hiss, eliminate tape saturation, reduce wow and flutter and clean up any tube distortion in the signal path during the analog (tape) recording process. Thus making the final product much more pristine and therefore better sounding to the listener.

Audiophile signal processing (Digital) - Really expensive esoteric rackmount effects processors and software plug-ins designed to emulate tape hiss, and tape saturation, induce wow and flutter and create tube distortion in the signal path during the digital recording process, thus making the final product much less pristine and therefore better sounding to the listener.

Baffle - A board or other plane surface used to mount a loudspeaker.

Bandwidth - The range of frequencies covered by a driver or a network (crossover).

Band-Pass filter - An electric circuit designed to pass only a certain range of frequencies. See also High-pass and Low-pass filters.

Basket - The metal frame of a speaker.

Bass Reflex - See ported enclosure.

Bi-amping - Means that instead of driving a speaker full-range with a single channel of amplification, through a single set of speaker cables, you actually connect two sets of cables, with each set driven by a separate amplifier, or separate channels of a multi-channel amplifier. This way, low, mid and high frequencies each receive dedicated amplification.

Booking Agent - A middle-aged man with a poorly glued toupee who tells you that it’s only 160 kilometres to the gig when in fact it’s 360 kilometres. The same guy who thought inserting a one-nighter in Fort Wayne Indiana between shows in San Diego and San Francisco was somehow a good idea.

Boomy - The smearing of transients that makes bass reproduction sound muddled.

Bridging - Combining both left and right stereo channels on an amplifier into one higher powered mono channel. When an amplifier is bridged, the impedance that each half of the amplifier actually "sees" is 1/2 of the loudspeaker’s impedance.

Channel - The path an audio signal travels through a circuit during playback.

Circuit - A complete path that allows electrical current from one terminal of a voltage source to the other terminal.

Clam - A really obvious mistake such as a wrong note or bad chord change. i.e., you meant to do one thing but screwed up instead. Usually followed by: “I thought you said D not E.” “Sorry I was reaching for my drink and I dropped my drum sticks.” “If it’s not too much trouble can you end the song at the same time as everyone else?” “I thought it was a good time to change the key of the song but you’re right, I should have told the rest of the band.” Also see Oyster.

Click Track - You can ignore this if you ever come across one. Everyone else does. Think of it like a metronome.

Clipping - (1) a distortion caused by cutting off the peaks of audio signals. Clipping usually occurs in the amplifier when its input signal is too high or when the volume control is turned too high and the amplifier tries to put out too much current and it sends out direct current to the speakers. (2) when playing at loud volumes, and the cone of the driver “bottoms out” - it cannot move as far as the signal requires it to, it can produce a noise. If an amplifier or speaker is left operating in this condition, serious damage may occur.

Continuous Average Power - The amount of power in a signal. Usually the signal is a sinewave used to test power amplifiers. This is calculated from the RMS voltage hence is often incorrectly called RMS watts. It is the voltage that is RMS, not the wattage. When this is done with a sinewave, this is the most conservative measurement of power. Often the power measurement is done over a very limited time period that is not stated. This avoids exposing a common weakness in many amplifier designs.

Count In - The one or two bar count that prepares the band for the beginning of the song. Usually, at least one band member is too busy checking out the crowd to be any part of this fundamental process.

Crossover Network (Filter) - An electric circuit or network that splits the audio frequencies into different bands for application to individual speakers. See Electronic and Passive Crossover.

Current (I) - The flow of electrical charge measured in amperes.

Damping - The reduction of movement of a speaker cone, due either to the electromechanical characteristics of the speaker driver and suspension, the effects of frictional losses inside a speaker enclosure, and/or by electrical means.

Decibel (dB) - (1) A logarithmic scale used to denote a change in the relative strength of an electric signal or acoustic wave. It is a standard unit for expressing the ratio between power and power level. An increase of +3dB is a doubling of electrical (or signal) power; an increase of +10dB is a doubling of perceived loudness. The decibel is not an absolute measurement, but indicates the relationship or ratio between two signal levels. (2) SPL (sound pressure level) can be measured in dB.

Diaphragm - The part of a dynamic loudspeaker attached to the voice coil that moves and produces the sound. It usually has the shape of a cone or dome.

Diffusion - The scattering of sound. Diffusion reduces the sense of direction of a sound source, a useful quality in surround speakers.

Direct Current (DC) - Current in only one direction.

Dispersion - The spreading of sound waves as it leaves a speaker.

Distortion - Any undesirable change or error in the reproduction of sound that alters the original signal.

Dome Tweeter - A high frequency speaker with a dome-shaped diaphragm.

Driver - A loudspeaker unit, consisting of the electromagnetic components of a speaker, typically a magnet and voice coil that actually converts electrical energy into sound.

Dynamic range - The range of sound intensity a system can reproduce without compressing or distorting the signal.

Efficiency rating - The loudspeaker parameter that shows the level of sound output when measured at a prescribed distance with a standard level of electrical energy fed into the speaker.

Electronic Crossover - Uses active circuitry to send signals to appropriate drivers. Usually more efficient than passive crossovers, however requires additional amplifiers to drive each frequency band.

Enclosure - The box that contains the driver(s).

Equalizer - Electronic device used to boost or attenuate certain frequencies.

Filter - Any electrical circuit or mechanical device that removes or attenuates energy at certain frequencies. See Crossover Network.

Flat Response - The faithful reproduction of an audio signal; specifically, the variations in output level of less than 1dB above or below a median level over the audio spectrum.

Frequency - The number of waves (or cycles) arriving at or passing a point in one second, expressed in hertz (Hz).

Frequency Response - The frequency range to which a system, or any part of it, can respond.

Full-range - A speaker designed to reproduce all or most of the sound spectrum.

Ground - Refers to a point of (usually) zero voltage, and can pertain to a power circuit or a signal circuit.

Harmonic - The multiple frequencies of a given sound, created by the interaction of signal waveforms.

Harmonic Distortion - Harmonics artificially added by an electrical circuit or speaker, and are generally undesirable. It is expressed as a percentage of the original signal. See THD.

Hertz (Hz) - A measurement of the frequency of sound vibration. One hertz is equal to one cycle per second. The hertz is named for H.R. Hertz, a German physicist. Also a good place to rent a car when you’re on vacation.

High-pass Filter - An electric circuit that passes high frequencies but blocks low ones. See Band-pass and Low-pass filters.

Horn - A speaker design using its own funnel shaped conduit to amplify, disperse, or modify the sounds generated by the internal diaphragm of the speaker.

Hum - Audio noise that has a steady low frequency pitch often caused by interference from the AC power line.

Imaging - Listening term - it is the speaker’s ability to locate where each instrument or voice is located.

Impedance - The opposition of a circuit or speaker to ac current; the combined effect of a speaker’s resistance, inductance, and capacitance that opposes the current fed to it. It is measured in ohms and varies with the frequency of the signal.

Infinite Baffle - A flat surface that completely isolates the back wave of a driver from the front.

Kilohertz (kHz) - One thousand hertz.

Low-Pass Filter - An electric circuit designed to pass only low frequencies. See Band-pass and High-pass filters.

Lobing - The tendency of a speaker system that consists of more than one driver to produce a lobed frequency response in space with in-phase reinforcement (lobes) from the various drivers occurring at some elevations and out-of-phase opposition (nulls) at points between the lobes.

Maximum power rating - A value which means almost nothing, but is used nonetheless by manufacturers to entice the unsuspecting into purchasing their product based solely on the big number. Technically, it is the maximum wattage that an audio component can deliver/handle as a brief burst during a musical peak. Most reputable manufacturers will provide both an RMS and Max power rating. Typically, the given value for the maximum power rating is twice to three times that of RMS.

Midbass - Mid level bass, usually frequencies just above the sub-bass range, from around 100-400Hz or so.

Midrange (mids) - The frequency range above bass but below treble that carries most of the identifying tones of music or speech. It is usually from 300- 400Hz to 3kHz or so.

Mono - Monophonic sound. A method for reproducing sound where the signals from all directions or sources are blended into a single channel.

MOSFET - Metal Oxide Semiconductor Field Effect Transistors.

Noise - Any undesirable sound reproduced in an audio system.

Octave - A range of tones where the highest tone occurs at twice the frequency of the lowest tone.

Ohm - A unit of electrical resistance or impedance.

Ohm’s Law - A basic law of electric circuits. It states that: the current [I] in amperes in a circuit is equal to the voltage [E] in volts divided by the resistance [R] in ohms; thus, I = E/R.

Out of Phase - When your speakers are mounted in reverse polarity, i.e., one speaker is wired +/+ and -/- from the amp and the other is wired +/- and -/+. Bass response will be very thin due to cancellation.

Oyster - A really big messy clam that usually lasts for more than one full measure. Also see Clam. (That will teach my boss not to proofread my work.)

Passive Crossover - Uses inductors (coils) and capacitors to direct proper frequencies to appropriate drivers.

Passive Radiator - A device that looks just like an ordinary driver, except it has no magnet or voice coil. A radiator is usually a highly compliant device, with a similar cone material and surround found on regular active drivers. The radiator must usually be at least as large (or larger) than the driver it is aligned with. The passive radiator is tuned and used in place of a port, providing bass reinforcement for the driver in a similar fashion as any regular ported box.

Peak - The maximum amplitude of a voltage or current.

Peak Power Rating - See Maximum power rating.

Phase - Refers to the timing relationship of two or more signals or soundwaves. It’s especially important to be sure that your stereo speakers are playing “in phase.” This means that the drivers (cones and domes) of your right and left speakers are moving in and out at the same time. If your speakers are “out of phase” you’ll hear significantly less bass, and instead of producing a strong center image, the sound tends to stay localized at the speakers.

Phase Coherence - The relationship and timing of sounds that come from different drivers.

Phase Distortion - A type of audible distortion caused by time delay between various parts of the signal; can be caused by equalizers.

Polarity - The orientation of magnetic or electric fields. The polarity of the incoming audio signal determines the direction of movement of the speaker cone. Must be observed when wiring speakers, so that they are “in phase”. See Out of Phase.

Ported Enclosure - A type of speaker enclosure that uses a duct or port to improve efficiency at low frequencies. Excellent design for lower power systems, as the port often adds up to +3dB to low frequency efficiency.

Rear fill - The ambience created by a pair of rear speakers that helps complete the soundstage.

Resonance - The tendency of an object to vibrate most at a particular frequency.

Resonance Frequency - The frequency at which the speaker tends to vibrate most at a certain frequency.

Resistance (Re) - In electrical or electronic circuits, a characteristic of a material that opposes the flow of electrons. Speakers have resistance that opposes current.

RMS volts - In an AC signal the instantaneous voltage is constantly varying. The RMS measuring process combines the the signal into a number that can be used to accurately calculate average power. Wattage calculated based on RMS voltage is correctly termed continuous average power. RMS power is an incorrect term usually used to represent continuous average sinewave power.

RMS watts - An incorrect term used to refer to continuous average sinewave wattage. This is the most conservative measure of power capability of audio equipment.

Roll-off (cut-off) - The attenuation that occurs at the lower or upper frequency range of a driver, network, or system. The roll-off frequency is usually defined as the frequency where response is reduced by -3dB.

Satellite Speaker - A small speaker with limited bass response, often designed to be used with a matching subwoofer.

Sealed enclosure - Air tight enclosure that completely isolates the back wave of the driver from the front.

Signal - The desired portion of electrical information.

Signal-to-noise (S/N) - The ratio, expressed in dB, between the signal and noise.

Sinewave - The waveform of a pure alternating current or voltage. It deviates equally above a zero point to a positive value and an equal negative value. Audio signals are sinewaves or combinations of sinewaves.

Soundman - The one person everyone in the band should treat really well ... but doesn’t. He or she is the hard working individual that can fix everything you own (including the band’s van) armed with nothing but a jackknife, a gum wrapper and gaffer tape. They also have the power to determine exactly how much of yourself you hear in the monitor mix, whether or not your vocals are dry and thin, or big and full with lots of effects. They are the person that spends your entire show with their hands closest to the ‘suck’ control, carefully hidden on any mixer.

Sound Pressure Level (SPL) - The loudness of an acoustic wave stated in dB that is proportional to the logarithm of its intensity.

Spider - The flexible material that supports the former, voice coil, and inside portion of the cone within the speaker frame.

Standing Wave - A buildup of sound level at a particular frequency that occurs when any dimension of the room is equal to any multiple of the wavelength. You would hear it as a peak in the frequency response of the room.

Sub-bass - Portion of bass that is very low, usually from 20Hz-100Hz or so.

Subwoofer - A loudspeaker designed to reproduce only bass frequencies.

Timbre - The quality of a sound related to its harmonic structure. Timbre is what gives a voice or instrument its sonic signature - why a trumpet and a saxophone sound different when they play the same note.

Three-way - A type of speaker system composed of three ranges of speakers, specifically a woofer, midrange, and tweeter.

Total Harmonic Distortion (THD) - The percentage, in relation to a pure input signal, of harmonically derived frequencies introduced in the sound reproducing circuitry and hi-fi equipment (including speakers).

Transient Response - The ability of a speaker to respond to any sudden change in the signal without blurring (smearing) the sound. A speaker that can react quickly to rapid changes in sound has “good transient response”.

Treble (highs) - The upper end of the audio spectrum reproduced by tweeters, usually 3-4kHz and up.

Tweeter - A speaker designed to reproduce the high or treble range of the sound spectrum.

Two-way - A type of speaker system composed of two ranges of speakers, usually a woofer and tweeter.

Voice coil - The wire wound around the speaker former. The former is mechanically connected to the speaker cone and causes the cone to vibrate in response to the audio current in the voice coil.

Volt (E) - A unit of measurement used to measure how much “pressure” is used to force electricity through a circuit.

Watt - A unit of electrical power. A watt of electrical power is the use of one joule of energy per second. Watts of electrical power equals volts times amperes.

Wavelength - The length of a sound wave in air. It can be found for any frequency by dividing the speed of sound in air (1120 feet per second) by the frequency of the sound, or: WL = 1120 / Freq.

Woofer - A bass loudspeaker designed to reproduce low-frequency sound only. A woofer and subwoofer are usually the similar type of loudspeaker, but their application (crossover frequency) differentiates them.