Glossary
A
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. (e.g., High output alternators can cause even more noise to flow on the car?s chassis.)
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. (e.g., When my system is really crankin? it draws 20 amps from my alternator.)
Amplitude: The level or strength of a signal. (e.g., A high-powered amplifier will raise the amplitude of your deck?s signal to over 50 volts.)
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. (e.g., My radio can?t pick up too much without the antenna all the way up.)
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.)
Auto reverse: In a cassette player, the feature in which the direction of tape travel changes automatically. (e.g., Since my car stereo is equipped with an auto-reverse mechanism, I won’t need to turn the tape over when one side has finished playing.)
Azimuth: The relationship of a tape head gap to the magnetic lines of flux on a recorded tape. (e.g., If the azimuth is out of alignment, the high-frequency response will be poor.)
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. (e.g., My friend?s installer used a bandpass filter to send just the mid range frequencies to his 6-inch speakers.)
Boost: To raise the level of a signal. The opposite of cut. (e.g., We used my equalizer to boost the highs going to my tweeters.)
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. (e.g., A feature for an in-dash installed car audio deck is the changer/controller function so that the trunk installed changer can be remotely accessed.)
Crossover Point: The frequency at which a crossover delivers equal power to each of its outputs. (e.g., A car audio subwoofer crossover point of 40 Hz passes only the lowest frequencies.)
Cut: A reduction in the level or amplitude of a signal. (e.g., Why don?t you cut your 3 kHz passband by lowering the 3.1 kHz slider on your equalizer?)
D
Damping: The process of reducing or eliminating vibrations, reverberations and/or oscillations. (e.g., In car audio often add a heavy, sticky damping material to any panels that tend to resonate and rattle.)
DCC and MD: Two additional formats for recorded material that stand for Digital Compact Cassette and MiniDisc, respectively. (e.g., Although it is rare to see DCC units in a car audio system, more and more MD players are being sold every day.)
Delaying: Adjusting the passage of time between two signals. (e.g., If I purchase a DSP system, I can delay one channel of my stereo, and move the images across the soundstage.)
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: Just 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.g., Modern CDs are capable of more than 90 dB of dynamic range, which is about twice as much as with old cassette tapes without noise reduction.)
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. (e.g., Most installers will use an equalizer to get a flat response in cars stereo.)
Frequency Response: How well a circuit or system transmits the frequencies that are applied to it. (e.g., The frequency response of my new amplifier was virtually flat from 20 Hz up to 20,000 Hz.)
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. (e.g., Humans can experience car audio sound from 20 Hz to over 20,000 Hz.)
Full Range: Containing or able to handle all the frequencies normally experienced by us humans (from 20 Hz up to 20,000 Hz). (e.g., A full range speaker is one that was designed as the only speaker in a car stereo.)
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. (e.g., For safety, a component installer will always add a fuse very near the positive battery post.)
G
Gain: The difference in the amplitude of two signals. This is commonly used to compare the input and output of an electronic component. (e.g., Richard?s tweeters were not loud enough, so he turned up the gain on his high-frequency crossover output.)
Graphic: The type of equalizer whose controls give some indication of the intended response. (e.g., A 9-band graphic equalizer usually has nine slider controls that move up and down to alter the electrical 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. (e.g., It is important to use quality transformers in a ground-loop isolator so that the signal will not be altered.)
H
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. (e.g., A compression driver usually uses a horn on its 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. (e.g., A frequency of 50 Hz means that something is repeating 50 times per second.)
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. (e.g., The resistance of a speaker?s voice coil may be measured at 3.1 ohms, but the impedance of that speaker may be 10 ohms at 50 Hz.)
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. (e.g., We used an inductor as a woofer coil.)
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. (e.g., The signal line level output of a good quality car stereo head unit will often exceed 3 volts.)
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. (e.g., We put a low pass woofer coil on John?s 6 x 9-inch speaker so that it would act like a car stereo subwoofer.)
M
Midbass: The range of frequencies just above the subwoofer and just below the midrange. (e.g., A good midbass driver will handle the bandwidth of 80 Hz up to 200 Hz.)
Midrange: The range of frequencies that lie between midbass and the high frequencies. (e.g., A good midrange speaker will handle from 200 Hz up to 2 kHz)
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. (e.g., Until we added motorization to our amp board, we had to remove about 20 screws by hand in order to get to the fuses.)
N
Noise Reduction (DNR, Dolby B, Dolby C, etc.): Various methods or schemes for reducing the level of noise on program material. Note that modern CDs don?t require such processing. (e.g., Since most of the old cassettes were recorded with Dolby B noise reduction, you should look for a cassette deck that features Dolby B on playback.)
Noise: An unwanted electrical signal or sound. (e.g., We told Frankie to watch out for that discount amp because it had too much noise.)
O
Octave: A doubling or halving of a frequency. (e.g., One octave higher than 100 Hz is 200 Hz and one octave lower than 100 Hz is 50 Hz.)
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. (e.g., We used a sine wave oscillator to tune Ralph?s woofer box.)
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. (e.g., You should save up for a good parametric equalizer so that you can dump your old 5 band graphic EQ.)
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. (e.g., We used two capacitors and one inductor to make a 6 dB/octave passive crossover for our midrange speakers.)
Phase: The time relationship between two AC (alternating current) signals. (e.g., In an AC circuit the current and voltage may experience a phase shift.)
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. (e.g., It is important to maintain similar polarity throughout an entire speaker system so that all the speakers will be working together.)
Ported: A type of bass reflex enclosure design that utilizes a hole, or port, to improve the low-frequency response. (e.g., In most cases a ported enclosure will thump harder than a sealed box, but not over as wide a range of frequencies.)
Power amplifier: The final stage of amplification. (e.g., You must use a power amplifier to drive your speakers.)
Preamplifier: The first stage of amplification in which the amplitude of a very low-level audio signal is increased. (e.g., Most car audio decks have four separate preamplifier outputs that correspond to the Front Left, Front Right, Rear Left, and Rear Right channel outputs.)
Q
R
RCA jacks: The coaxial connectors commonly used to interlink components in the world of car audio. (e.g., My AM/FM/CD player has four RCA jacks that send the signal on to my four channel amplifier.)
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. (e.g., In order to get our power doors locks to work automatically with our new alarm, you will have to purchase two 12 volt relays for each door.)
Removable Face: The type of dash installed deck that permits the controls and display to be easily removed for security. (e.g., We bought a removable face deck because we didn?t want to carry around the entire player.)
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. (e.g., We used an RTA to adjust my equalizer.)
S
Scan: When a tuner stops at each programmed station for about five seconds to give the listener a chance to select that station. (e.g., John?s old AM/FM/Cassette player doesn?t even have a scan feature so he has to tune all his stations one at a time.)
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. (e.g., You should use a sealed enclosure only if your woofer was designed for that type of box.)
Search: A fast forward or fast reverse feature of both cassettes and CDs that permit the listener to find a particular passage. (e.g., Using music search lets me move quickly up to the right part of the song.)
Seek: When a tuner stops at each strong station. (e.g., I only use seek tuning when I?m in a new area and don?t know the stations.)
Sensitivity: The control on a component that adjusts the gain of an electronic circuit. (e.g., Most power amplifiers will produce minimum hiss when the sensitivity control is set to its minimum.)
Sine Wave: A waveform that is commonly used to test and set up audio systems. (e.g., We checked out our subwoofer enclosure by sending it a 50 Hz sine wave and measuring the response.)
Skip: When a CD player quickly advances up to the start of the track. (e.g., I like the skip feature when I get a new CD and want to check it out fast.)
Slope: The rate of rise or fall of a filter, usually expressed in a number of dB per octave. (e.g., John?s crossover had a 12 dB/octave slope on high output and a 18 dB/octave slope on the low output.)
Soundstage: The psychoacoustic effect that takes place when two or more channels of program material acoustically interact with our human brains. (e.g., By paying attention to the left and right path lengths of the front speakers, Sandy found that her front soundstage improved tremendously.)
SPL: A measured value of the pressure of sound expressed in dB. (e.g., After installing four 12-inch woofers and 200 watts more power, Jack?s system cranked out a very respectable 124 dB SPL.)
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. (e.g., The reason that we installed 2 farads of Stiffening Capacitors was so that we could stop our headlights from dimming whenever the bass hit hard.)
T
Tweeter: A speaker designed to reproduce only the high frequencies such as 3500 Hz and above. (e.g., A tweeter can be damaged when driven by low frequencies so you should always use the proper crossover.)
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. (e.g., When something fails in a speaker that is properly installed, it is usually the voice coil.)
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. (e.g., A potential of one volt will cause one amp of current to flow through a resistance of one ohm.)
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. (e.g., Whenever a current of 20 amps flows through a resistor with 12 volts across it, that resistor will have to handle 240 watts of power.)
X
Y
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