Car Stereo Glossary

Acoustic Feedback

A squealing sound when the output of an audio circuit is fed back in phase into the circuit's input.

Acoustic Fiberfill

Thin fiberglass or polyester fiberfill material used as damping material inside speaker enclosures. Typically available at sewing centers for stuffing pillows.

Acoustic Suspension

A speaker designed for, or used in, a sealed enclosure.

Acoustics

The science or study of sound.

Air Suspension

An acoustic suspension speaker.

Alternating Current (AC)

An electrical current that periodically changes in magnitude and direction.

Ambience

A surround or concert-hall sound.

Ampere (A)

The unit of measurement for electrical current in coulombs (6.25 x 1018 electrons) per second. There is one ampere in a circuit that has one ohm resistance when one volt is applied to the circuit. See Ohm's law.

Amplifier

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

Amplitude

The relative strength (magnitude) of an electrical signal above or below some reference, often ground or zero. Amplitude can be expressed as either a negative or positive number, depending on the signals being compared; usually measured in volts or amperes.

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 20,000 Hz.

Baffle

A piece of wood inside an enclosure used to direct or block the movement of sound.

Balance

Equal signal strength provided to both left and right stereo channels.

Bandpass Filter

The metal frame of a speaker.

Basket

A speaker designed for, or used in, a sealed enclosure.

Bass

A ported reflex speaker enclosure.

Bass Reflex

A speaker designed for, or used in, a sealed enclosure.

Battens

Small strips of wood placed inside a speaker to reinforce its mating corners or to provide a mounting surface for front and back panels.

Bobbin

A paper, plastic, or metal cylinder around which is wound the wire that forms a speaker's voice coil. The bobbin is mechanically connected to the speaker cone.

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 impedance to an ac current.

Cassette

1. The two-reel plastic carrier that contains audio magnetic tape.
2. The shortened name for the automotive sound system component that plays the audio magnetic tape contained in cassettes.
CD
Compact disc or the compact disc player.

Channel

The left or right signals or a stereo audio system.

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 its input signal is too high or when the volume control is turned up too high.

Coaxial Driver

A speaker that is 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

"Smearing" sounds by adding frequencies due to intermodulation distortion. More prevalent at high audio frequencies.

Compliance

The relative stiffness of a speaker suspension, typically indicated simply as "high" or "Low", but technically specified as Vas.

Cone

The cone-shaped diaphragm of a speaker attached to the voice coil. It produces pulsations of air that the ear detects as sound.

Crossover Network

An electric circuit or network that splits the audio frequencies into different bands for application to individual speakers.

Current

The flow of charge measured in amperes.

Damping

1. Acoustic fiberglass or polyester fiberfill material used inside speaker enclosures.
2. The reduction of movement of a speaker cone, due either to the electromechanical characteristics of the speaker driver and suspension, or the effects of pressure inside a speaker enclosure.

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 level P1 and power level P2 dB - 10 log10 P1/P2. 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, actually, but indicates the relationship or ratio between two signal levels.

DIN-C

A set of standard specifications for automotive head-units with two shaft openings and a rectangular opening.

DIN-E

A set of standard specifications for automotive head-units with a single rectangular opening. Commonly called "flat-face" design.

Direct Current

Current in only one direction.

Dispersion

The spreading of sound waves as they leave a speaker.

Distortion

Any undesirable change in the characteristics of a reproduced audio signal that degrades the fidelity of the original signal.

Dolby

A type of dynamic noise reduction system.

Dome Tweeter

A high frequency speaker with a dome-shaped diaphragm that provides much better dispersion of high frequencies than standard cone speakers.

Driver

Technically, the electromagnetic components of a speaker, typically consisting of a magnet and voice coil, but also used to describe any direct radiator speaker.

Dual Voice-Coil

Two voice coils wound on the same bobbin and driving the same cone.

Ducted Port

A ported reflex speaker enclosure.

Dynamic-Range

The range of sound levels, from softest to loudest, which a system can reproduce without distortion. Usually expressed in decibels.

Enclosure

A housing for any electrical or electronic device.

Equalizer

An adjustable audio filter inserted in a circuit or system to divide and adjust its frequency response.

Equalization

As used in audio, the adjustment of frequency response to tailor the sound to match personal preferences, room acoustics, and speaker enclosure design.

Fader

A variable control used to change the distribution of power between front and rear speakers.

Farad

The basic unit of capacitance. A capacitor has a value of one farad when it can store one coulomb of charge with one volt across it.

Fidelity

A measure of how true a circuit, amplifier, system or subsystem reproduces it input signal.

Filter

An electrical circuit designed to prevent or reduce the passage of certain frequencies.

Flat Response

The faithful reproduction of an audio signal; specifically, variations in output level of less than one decibel above or below a median level over the audio spectrum.

Free-Air Resonance

The natural resonant frequency of a woofer speaker when operating outside an enclosure.

Frequency

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

Frequency Response

A plot of how a range of frequencies are faithfully reproduced by a given speaker or audio system.

Fundamental or Fundamental Tone

The tone produced by the lowest frequency component of an audio signal.

Full-Range

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

Golden Ratio

The ratio of the depth, width, and height of a speaker enclosure, based on the Greek Golden Rectangle, and which most often provides the best sound. W = 1.0, Depth = 0.6W, Height = 1.6W

Grill Cloth

Fabric used to cover the speaker mounted in an enclosure.

Ground

Refers to a point of (usually) zero voltage, and can pertain to a power circuit or a signal circuit. Commonly used as the reference point for voltage measurements.

Harmonic

The multiple frequencies of a given sound, created by the interaction of signal waveforms. A "middle C" on the piano has a fundamental audio frequency of 256 Hz, but also a number of secondary higher frequencies (harmonics) that are odd and even multiples of this fundamental.

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.

Head Unit

The name given to automotive sound system component that supplies the main signal source from Am, Fm, cassette tape or CD player.

Hertz

A unit of frequency equal to one cycle per second, named after German physicist H.R. Hertz.

High Fidelity

Commonly called hi-fi, it refers to the reproduction of sound with little or no distortion.

High-Pass Filter

An electric circuit designed to pass only high frequencies. See also bandpass filter and low-bass filter.

Hiss

Audio noise that sounds like air escaping from a tire.

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, typically caused by the effects of induction by nearby ac lines or leakage of ac line frequency into an amplifier's signal circuits.

Impedance

The opposition of a circuit or speaker to an alternating current.

Inductance

The capability of a coil to store energy in a magnetic field surrounding it. It produces impedance to an ac current.

Intensity

The strength of a sound signal represented by the amplitude of the pressure waves producing the sound. Expressed watts per square meter.

Intermodulation Distortion

Combinations of two or more frequencies which generate new frequencies which are sums and differences of the original signal.

L-Pad

A type of potentiometer that maintains constant impedance at its input while varying the signal level at its output. L-pads are most often used as an external balance control or variable attenuator (volume control).

Loudness

A measure of the sensitivity of human hearing to the strength of sound.

Low-Pass Filter

An electric circuit designed to pass only low frequencies. See also bandpass filter and high-pass filter.

Microphone

A device that converts sound waves into electrical signals.

Midrange

A speaker designed to reproduce the middle frequencies of the sound spectrum, generally most efficient between about 1000 Hz to 4000 Hz.

Mounting Flange

The outer edges of a speaker frame which has pre-drilled holes to accept screws or bolts for securing it to the enclosure.

Noise

Any unwanted signal or electromagnetic radiation, particularly that which distorts signals or disrupts normal operation.

Noise Factor / Figure

For a given bandwidth, the ratio of total noise power ratio at the input to the noise power ratio at the output when the ratio is expressed in dB, it is noise figure.

Octave

The logarithmic relation of sound frequencies used by musicians. The frequency of each higher octave is twice the preceding one.

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.

Passive Radiator (or Drone)

A speaker with a cone but no driver components. The cone vibrates with the change in pressure inside the speaker enclosure. Typically used to increase bass output with no increase in electrical power.

Peak

The maximum amplitude of a voltage or current.

Period

For electronic circuits, the length of time required for one cycle of a periodic wave.

Phase

The angular or time displacement between the voltage and current in an ac circuit.

Phase Distortion

The distortion which occurs when one frequency component of a complex input signal takes longer to pass through an amplifier or system than another frequency.

Pitch

How a tone sounds to the human ear. It is a subjective term because the perception of frequency varies with sound intensity.

Piezoelectric

A characteristic of some materials, especially crystal, that when subjected to electric voltage the material vibrates. Sometimes used in tweeters in place of a magnet, voice coil and cone.

Polarity

The orientation of magnetic or electric fields. The polarity of the incoming audio signal determines the direction of movement of the speaker cone.

Ported Reflex

A type of speaker enclosure that uses a duct or port to improve efficiency at low frequencies.

Power

The time rate of doing work or the rate at which energy is used. A watt of electrical power is the use of one joule of energy per second. Watts of electrical energy equals volts times amperes.

Resonance

The tendency of a speaker to vibrate most at a particular frequency; sometimes referred to a natural frequency.

Resistance

In electrical or electronic circuits, a characteristic of a material that opposes the flow of electrons. It results in loss of energy in a circuit dissipated as heat. Speakers have resistance that opposes current.

RMS

An acronym for root mean square. The RMS value of an alternating current produces the same heating effect in a circuit as the same value of a direct current.

Selectivity

The characteristic that describes the ability of a tuned circuit or a receiver to select the signal frequencies desired and reject the ones not desired.

Sensitivity

A measure of the ability of a receiver to amplify weak signals.

Signal

The desired portion of electrical information.

Signal-to-Noise

The ratio, expressed in dB, between the signal (sound you want) and noise (sound you don't want).

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

The vibratory energy of air particles. The signals of frequencies from 20 to 20 kHz that normally are detected by the human ear.

Sound Pressure Level (SPL)

The loudness of an acoustic wave stated in dB that is proportional to the logarithm of its intensity.

Spectrum

The complete range of frequencies from the lowest to highest.

Spider

The flexible fabric that supports the bobbin, voce coil, and inside portion of the cone within the speaker frame.

Static

Random noise in a communications system receiver due to atmospheric or manmade electrical disturbances.

Subwoofer

A speaker especially designed to handle the bass portion (20 Hz to 150 Hz) of the audio spectrum.

Surround

The outer suspension of a speaker cone; the surround connects the outside portion of the cone to the speaker frame.

Suspension

See Surround.

Three-Way

A type of speaker system composed of three ranges of speakers, specifically a tweeter, mid-range and woofer. See also two-way.

Timbre

A subjective term used for human hearing that gives a sound a particular identity. It is related to the spectrum of frequencies contained within the sound.

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 the speakers).

Transient Response

The instantaneous change is an electronic circuit's output response when input circuit conditions suddenly change from one steady-state condition to another.

Transient Intermodulation Distortion

A distortion which occurs principally during loud, high frequency music passages in solid-state amplifiers that use large amounts of negative feedback.

Treble

The upper end of the audio spectrum usually reproduced by a tweeter.

Trivial Driver

A speaker that is composed of three individual voice coils and cones; used for the reproduction of sounds in three segments of the sound spectrum. See also coaxial driver.

Tuner

The part of a radio or TV receiver containing the rf amplifier, mixer and local oscillator that selects the desired signal.

Tweeter

A speaker designed to reproduce the high or treble range of the sound spectrum, generally most efficient from about 4000 Hz to 20,000 Hz.

Two-Way

A type of speaker system composed of two ranges of speakers, consisting of any two of the following: a tweeter, midrange, and woofer. See also three-way. Some midrange speakers are classified as midrange/tweeter.

Voice Coil

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

Watt

A unit of electrical power.

Wavelength

The distance a wave travels in the time required to complete one cycle.

Whizzer

A small supplementary cone attached to the center of the speaker's main cone for the purpose of increasing high frequency response.

Woofer

A speaker designed to reproduce the low frequencies of the sound spectrum, generally most efficient from about 20 Hz to 1000 Hz.