Audio Glossary

 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.

Attenuation - the reduction, typically by some controlled amount, of an electrical signal.

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

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 Enclosure - see dual reflex bandpass and single reflex bandpass.

Band-pass filter - an electric circuit designed to pass only middle frequencies. See also High-pass and Low-pass filters.

Basket - the metal frame of a speaker.

Bass (lows) - The low end of the audio frequency spectrum, from approximately 20 Hz up to 400 Hz or so.

Bass Reflex - a ported enclosure.

Beaming - the tendency of a loudspeaker to concentrate the sound in a narrow path instead of spreading it.

Boomy - the smearing of transients that makes bass reproduction sound muddled, usually because of improperly designed sealed (to small), ported (to  small or tuned improperly), and bandpass enclosures, although the latter are sometimes designed this way on purpose by car audio manufacturers or install  shops to be loud.

Bridging - combining both left and right stereo channels on an automotive amplifier into one higher powered mono channel. When an amplifier is bridged, the impedance that the amplifier actually "sees" is calculated based upon the output of both stereo channels. Here is a simple formula to help define this:

Bridged Mono Impedance = (Y / X)/2

 Y = impedance of driver(s) (both drivers should be identical)

 X = # of drivers in circuit

 So, hooking up one 4 ohm sub bridged mono would be equal to hooking up two 2 ohm subs in stereo, one to each channel.

Capacitor - a device made up of two metallic plates separated by a dielectric (insulating material). Used to store electrical energy in the electrostatic field between the plates. It produces an impedance to an ac current. In automotive applications, special "Power Line Caps" can be connected inline to the amplifier to aid the alternator in supplying current demands of amps. Non-polarized capacitors can be used as first order passive high pass crossovers, or as components in more complex high pass, bandpass and lowpass crossovers. See power line caps.

Center Channel - in home theater, sound decoded from the stereo signal sent to a speaker mounted in front of the listener, specially designed to enhance voices and sound effects from a movie soundtrack. Used in car audio to help offset skewed stereo imaging due to seating positions in the automotive environment.

Channel - the path an audio signal travels through a circuit during playback. At least 2 channels are required for stereo sound.

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

Clipping - a distortion caused by cutting off the peaks of audio signals. Clipping usually occurs in the amplifier when it's input signal is too high or when the volume control is turned to high.

Coaxial Driver - a speaker composed of two individual voice coils and cones; used for reproduction of sounds in two segments of the sound spectrum. See also triaxial driver.

Coloration - any change in the character of sound that reduces naturalness, such as an overemphasis of certain tones.

Cone - the cone-shaped diaphragm of a speaker attached to the voice coil which produces pulsation's of air that the ear detects as sound.

Crossover Frequency - the frequency at which a driver's response is down -3dB. See Roll-off.

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.

Damping Material - any material added to the interior of a speaker enclosure to absorb sound and reduce out-of-phase reflection to the driver diaphragm (cone). Usually acoustic fiberglass, polyester batting, or Polyfill is used in speaker enclosures.

Decibel (dB) - 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 +3 dB is a doubling of electrical (or signal) power; an increase of +10 dB is a doubling of perceived loudness. The decibel is not an absolute measurement, but indicates the relationship or ratio between two signal levels.

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.

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.

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

Electronic Crossover - uses active circuitry to send signals to appropriate drivers. More efficient than passive crossovers.

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 1 dB 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. Unless a limit of variation in intensity is stated, this specification is meaningless. i.e., you see a subwoofer in a ported enclosure with a rated response of 35 - 300 Hz. Means nothing. It could very well be that it is 35 - 300 Hz (-24 dB), which means the low frequency roll-off actually begins at around 70 Hz. It needs to read something like this: 35 - 300 Hz (- 3 dB), which gives 35 Hz as the actual roll off frequency.

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. In car audio, the single most important factor to avoid unwanted noise is finding and setting a good ground.

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.

Head Unit - the in dash control center of a car audio system, usually consisting of an internal low powered amp, AM/FM receiver, and either a tape or CD player (or both).

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.

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

Hiss - audio noise that sounds like air escaping from a tire.

Home Theater - an audio system designed to reproduce the theater sound experience while viewing movies in the home. Minimally consisting of a Dolby Pro Logic® surround sound receiver, left and right front speakers, a center channel speaker, and at least (1) surround sound speaker. These plus optional subwoofer(s), surround speaker(s), and digital formats such as Dolby Digital® can enhance the viewing experience by drastically improving the sound quality of movie soundtracks.

Hum - audio noise that has a steady low frequency pitch.

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.

Inductance (L) - the capability of a coil to store energy in a magnetic field surrounding it. It produces an impedance to an ac current. Inductors are commonly used in audio as low pass crossovers. See Le.

Input - the current fed into a loudspeaker.

Kilohertz (kHz) - one thousand hertz.

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

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. Automotive head units are a good example of this shady technique, as all the ones I have ever seen use this rating for the built in amplifier output. Use RMS for determining real world equipment capabilities. See WLS.

Midbass - mid level bass, usually frequencies just above the sub-bass range, from around 100 - 400 Hz 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 - 400 Hz 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. Used in most modern, quality car audio amplifiers in the power supply (and sometimes in the output stage). MOSFET's run cooler than normal bipolar transistors, and have a faster switching speed.

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.

Output - the sound level produced by a loudspeaker.

Passive Crossover - uses inductors (coils) and capacitors to direct proper frequencies to appropriate drivers. These crossover systems can be simple (First Order = 1 component @ -6 dB/octave slope) to complex (Fourth Order = 4 components @ -24 dB/octave slope).

Peak - the maximum amplitude of a voltage or current.

Peak-to-Peak power rating - a totally unreliable value of rating power amplifiers, often 4 times (or more!) the actual RMS output. See WLS.

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.

Resonance - the tendency of a speaker to vibrate most at a particular frequency.

Resonance Frequency - the frequency at which any system vibrates naturally when excited by a stimulus.

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 - an acronym for "root mean square." Used in audio to help rate the continuous power output of an amplifier or input capability of speakers. This is the preferred method for comparing anything in audio applications.

Signal - the desired portion of electrical information.

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

Sine wave - the waveform of a pure alternating current or voltage. It deviates about a zero point to a positive value and a negative value. Audio signals are sine waves or combinations of sine waves.

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

Sound Stage - the sound systems ability to correctly place instruments on an imaginary soundstage; reproduction of the way the music would sound if you were actually watching the musicians play in front of you. The stage should always appear to be in front of you, with a proper "image" of where each musician is playing on the imaginary soundstage.

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 is dependent upon the dimensions of a resonant room, car interior, or enclosure. It occurs when the rate of energy loss equals the rate of energy input into the system. This is what you hear when you listen into a sea shell.

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

Subwoofer - a loudspeaker designed to reproduce sub-bass frequencies.

Surround (suspension) - the outer suspension of a speaker cone; holds the diaphragm in place but allows it to move when activated. Usually made of foam or rubber.

Surround Sound - usually representative of the monophonic sound extracted from the stereo signal sent to smaller rear or side speakers used in a home theater.

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).

Treble (highs) - the upper end of the audio spectrum reproduced by tweeters, usually 3 - 4 kHz 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 same type of loudspeaker, but their application (crossover frequency) differentiates them.

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