Active: The circuitry that requires a supply of power and usually uses transistors, integrated circuits, and/or printed circuit boards. (e.g., By using an active crossover, it is much easier to achieve 18 dB/octave or 24 dB/octave slopes.)

Alternator: The electricity producing device in a car that charges the battery, powers all the electrical accessories when the engine is running, and sometimes causes alternator whine in car audio systems.

Amp or Amperage: The amount of current flowing in a circuit. In a 12-volt world, we use lots of amps to operate our accessories.

Amplitude: The level or strength of a signal.

Analog: The signal whose instantaneous value is a replication of another event or signal. (e.g., The digital bits on a compact disc are converted to an analog signal inside the D/A converter of the deck so that our brains can understand the software.)

Antenna: The rod that is used to receive radio waves in a car.

Attenuate: A reduction in the level of a signal. (e.g., I had to attenuate the signal level from my deck so that I wouldn't clip the input to my amp so much.)

B

Balance: The condition of a car audio stereo system in which both channels are reproducing the same level.

Balanced Transmission System: A circuit topology that maintains an equal impedance between both conductors and ground. A balanced transmission must have three basic elements: 1) Balanced Transmitter, 2) Balanced Transmission Line, 3) Balanced Receiver.

Bandpass: A filter that transmits a certain frequency band and attenuates frequencies that lie on both sides of that band.

Boost: To raise the level of a signal. The opposite of cut.

Bridged: The condition that exists when a load is connected across two active channels that are fed with the same input signal, but one of the channels is operated out-of-phase with respect to the other.

C

Channel: One half of the electrical and acoustical requirement for a basic stereo system. When two channels are reproduced correctly, the stereo effect will reproduce images across a soundstage.

Circuit Breaker: A re-settable protection device that amounts to a fuse that never needs replacement.

Coaxial Cable: The type of signal cable construction in which one insulated conductor is centered inside an outer cylindrical conductor.

Cone: The sound-making part of a dynamic loudspeaker that moves back and forth in the air.

Controller: The component or device that remotely operates the changer.

Crossover Point: The frequency at which a crossover delivers equal power to each of its outputs. 

Cut: A reduction in the level or amplitude of a signal.

D

Damping: The process of reducing or eliminating vibrations, reverberations and/or oscillations.

Delaying: Adjusting the passage of time between two signals.

DIN: The initials stand for German Industrial Standard and in car audio can be used to describe a standard dash opening for a deck or a multi-pin connector used in lieu of a RCA connector.

Distortion: Undesirable alteration in a signal.

Driver: Another word for a car stereo speaker.

Dual-Voice Coil: A particular car audio speaker design that uses separate voice coils connected to the same speaker cone.

Dynamic Range: The difference between the maximum signal level and the noise floor.

E

Enclosure: A mechanical device designed to improve the performance of a loudspeaker.

Equalization: The process of effecting a particular frequency response.

F

Fader: The control that varies the amplitude of the front vs. rear sound.

Flat: A response that is relatively linear from the lowest to the highest audible frequencies.

Frequency Response: How well a circuit or system transmits the frequencies that are applied to it.

Frequency: Simply the number of events or cycles that occur in a time period, usually one second. Frequency is measured in Hertz (Hz), which are the number of cycles per second.

Full Range: Containing or able to handle all the frequencies normally experienced by us humans (from 20 Hz up to 20,000 Hz).

Fuse: A simple device that limits the current flowing in a circuit and therefore protects the alternator, battery, electrical wiring, and the components. The current flow is disrupted when the fuse element melts and opens the circuit.

G

Gain: The difference in the amplitude of two signals. This is commonly used to compare the input and output of an electronic component.

Graphic: The type of equalizer whose controls give some indication of the intended response.

Ground-Loop Isolator: A transformer, usually with a 1:1 turns ratio, that is used to pass the AC signal from one component to the next component, but block the DC ground return between the components. Commonly used to eliminate ground-loop type alternator whine from car audio systems.

Head Amplifier: An active device designed to increase the signal level at the output of the deck.

High pass: A filter that permits the highs to go through, but attenuates the lows.

Horn: A speaker design scheme in which the cross-sectional area is constantly increasing from input to output.

Hz (short for Hertz): The term that stands for events or cycles per second. 1 kHz=1000 Hz, 1 MHz=1,000,000 Hz, 1 GHz=1,000,000,000 Hz.

I

Imaging: When two or more channels are reproduced in such a manner that our brains are tricked into hearing something that does not really exist. A phantom center is created when identical mono information is reproduced in two identical loudspeakers with a listener seated in between and in front of the two speakers.

Impedance: Resistance to the flow of alternating current.

Inductor: Usually a coil of wire that may or may not be placed in a magnetic field. It stores energy in the magnetic field and can be used to alter AC signals.

Isolation: A term that describes the impedance between the power supply and the signal path of component. It is an indication of power supply noise immunity.

J

K

L

Line level: The signal output of a deck or component that is usually not run through the speaker amplifier stages. Therefore the signal is much cleaner and more suitable for amplification.

Local/distant: A switch on an FM tuner that attenuates the signal strength of very strong signals so that they don’t overpower the tuner. This switch should normally be in the distant position.

Low pass: A filter that passes low frequencies and attenuates high frequencies.

M

Midbass: The range of frequencies just above the subwoofer and just below the midrange.

Midrange: The range of frequencies that lie between midbass and the high frequencies.

Motorization: When an electric motor or solenoid device is used to physically move a panel, plate, etc. for the purpose of highlighting certain elements of a car audio system.

N

Noise: An unwanted electrical signal or sound.

O

Octave: A doubling or halving of a frequency.

Ohm: The basic unit of electrical resistance. (e.g., One ohm is defined as the resistance that causes one volt to drop for each amp flowing through the resistance.)

Oscillator: A circuit that causes its output to vary periodically.

P

Parallel: A circuit topology that connects multiple circuits to the same connectors. (e.g., We connected four 8 ohm woofers in parallel so that we could really load down our amplifier.)

Parametric: A type of equalizer that permits the center frequency, the filter shape, and the amplitude of each band to be varied.

Passive: The type of circuitry that does <I>not<P> require external power, but rather uses only basic circuit elements such as capacitors, inductors, and resistors.

Phase: The time relationship between two AC (alternating current) signals.

Polarity: The direction or polarization of a signal entering or leaving a component. For instance, if a positive signal is applied to the input of a device, and that device emits a positive signal, then it is said to be a non-inverting device. Polarity merely describes a direction and should not be confused with phase.

Ported: A type of bass reflex enclosure design that utilizes a hole, or port, to improve the low-frequency response.

Power amplifier: The final stage of amplification.

Preamplifier: The first stage of amplification in which the amplitude of a very low-level audio signal is increased.

Q

R

RCA jacks: The coaxial connectors commonly used to interlink components in the world of car audio.

Relay: An electromechanical device that permits a small amount of current to control a much larger amount of current. A 12-volt automotive relay typically draws less than 100 mA but can switch 30 amps or more.

Removable Face: The type of dash installed deck that permits the controls and display to be easily removed for security.

RTA (Real Time Analyzer): A real time analyzer is used to measure the amplitude of several frequencies throughout the audio bandwidth of 20 Hz up to 20, 000 Hz.

S

Scan: When a tuner stops at each programmed station for about five seconds to give the listener a chance to select that station.

Sealed enclosure: The type of woofer box that separates the back wave from the front wave and still contains the back wave within the box.

Search: A fast forward or fast reverse feature of both cassettes and CDs that permit the listener to find a particular passage.

Seek: When a tuner stops at each strong station.

Sensitivity: The control on a component that adjusts the gain of an electronic circuit.

Sine Wave: A waveform that is commonly used to test and set up audio systems.

Skip: When a CD player quickly advances up to the start of the track.

Slope: The rate of rise or fall of a filter, usually expressed in a number of dB per octave.

Soundstage: The psychoacoustic effect that takes place when two or more channels of program material acoustically interact with our human brains.

SPL: A measured value of the pressure of sound expressed in dB.

Stiffening Capacitor: This term refers to a large value electrolytic capacitor that is used to improve the peak power handling capacity of a car audio system using amplifiers with switching power supplies.

T

Tweeter: A speaker designed to reproduce only the high frequencies such as 3500 Hz and above.

U

V

Voice Coil: The part of a speaker that consists of a small coil of small wire positioned very close to a permanent magnetic field. When electrical current is fed into the voice coil, the coil will either move forward or backward due to its interaction with the magnetic field. When the cone of a speaker is fastened to the voice coil, the cone will move.

Volt: Basic unit of potential difference. We often talk about car audio as a 12-volt world because our car batteries supply a nominal 12 volts.

W

Watt: The basic unit of power. From Ohm's Law we learn that power (measured in watts) dissipated by a load is equal to the voltage placed across that load multiplied by the current flowing through that load.

X

Y

Z