Glossary - Car Audio Plus

The information is split into 2 glossaries, Product Glossary and Technical Glossary

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Product Glossary

Acoustic Shelf – A shelf professionally machined from MDF that replicates your original parcel shelf, that you typically mount (6"x9") speakers to, underneath. Not only do they improve the bass response of your speakers but also deceive a would-be-thief.

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

Aerial Adapter
An adapter that will make your existing aerial, compatible with radios that have the conventional male plug socket. VW’s and Audi’s require a different adapter because their aerial is amplified for better reception.

Attenuate – To reduce or turn down (basically to mute the sound)

Auto Blank Skip - Usually accompanies track search and allows the user to skip from the end of one track to the beginning of the next missing out any blank or unrecorded passages on the tape.

Automatic Volume Control - Head unit's volume automatically increases as the car’s speed increases to compensate for the extra noise. An example is the JVC Cruise Control.

Auto Store - Benefits long distance drivers by scanning the airwaves in the area where you are travelling, and automatically storing five or six strongest stations in order of signal strength.

Azimuth - The angle at which the tape passes over the replay head. Any deviation from 90 degrees causes a loss in high frequencies (audible as a ‘dulling’ of the sound).

Balance – Equal signal strength provided to both left and right stereo channels of your radio.

Band Pass Filter – An electric circuit designed to pass only mid range frequencies.

Bass Reflex – A ported reflex speaker enclosure.

Bridgeable Amplifier – A 2 channel (stereo) amplifier on which both outputs cab be combined to make a mono amplifier of approx twice the power rating. Also applies to four channel amplifiers where outputs can be combined to make a more powerful, 2 channel (stereo) amplifiers.

Bridgeable to mono – As above.

CD Player – Compact Disc Player In-dash players are combined with a radio.

CD Changer – Compact Disc player unit that holds multiple CDs and mounts in the boot or under a seat. They can hold (6, 8, 10 or 12) discs depending on the make and model. It is connected to your radio by a Bus lead, which is hidden under the carpet and operated by your radio. Can be bought individually or together with a radio as a package.

CD Changer Package

A Package comprising of a radio, Compact Disc changer unit and a connecting lead. Radio can be a cassette/radio, CD/radio, MD/radio or MP3/radio.

CD Text – Enables the CD title, artist and track name to be displayed on compatible head unit displays.

Closed Box – Also known as ‘infinite baffle’ and meaning a speaker enclosure which is completely sealed.

Coaxial - Speakers that have two separate drive units (normally a small woofer and tweeter) moving independently. Essentially this gives better high frequency response and hence greater audio range and clarity. Also known as a 2-way speaker.

Components - Separate speakers usually a tweeter and a mid-range with an appropriate crossover.

Crossover – An electric circuit that splits the audio frequencies into different bands for application to individual speakers, bass to the woofers and Treble to tweeters, etc. A ‘passive crossover’ filters signals after they have been amplified, and don’t require power. An ‘active crossover’ (more effective and flexible) filters signals before amplification, sending different signals to different amps, these require power.

Crosstalk - also called ‘separation’ is a measurement indicating the amount of isolation between the channels of a stereo system, expressed in decibels. The higher the figure, the better the imaging will be.

CT - Clock Time. See RDS

Custom File – Allows you to memorise individual titles for each disc ‘Disc Memo’ and ‘Bank’ files of your favourite tracks.

DAB - Digital Audio Broadcasting is a new digital radio technology offering crystal clear sound with no interference. DAB radios have been developed to receive new DAB only radio stations that play on a predetermined unchangeable radio frequency throughout the UK. Eliminated the need to re-tune your radio as you change your regional location. 

DAC - Digital-to-Analogue Converter

DAT - Digital Audio Tape. A Medium used for reproducing pre-recorded material in digital format on tape - not to be confused with DCC.

D Bass – Dynamic Bass Boosts specific lower bass frequencies without mashing the overall clarity of sound.

DCC - Philips Digital Compact Cassette, a medium of digital cassette designed to replace the conventional analogue cassette.

Detachable Face – Sometimes referred to as ‘Removable Panel’ or ‘Theft Deterrent Faceplate’. A feature on the majority of modern radios, you physically remove the front fascia panel of the radio when you leave the car and pop it into the included robust case. A thief has no use for the back of the radio without a front panel.

DIN E - Deutsche Industrie Norm. German standard used by most manufacturers for the measurement of the radio aperture provided. Din is also used to describe multi pin plugs used for interconnections.

DNR - Dynamic Noise Reduction, Similar to Dolby but not as effective.

Dolby B and C – Noise-reduction systems used to reduce hiss in tape reproduction. Named after the inventor, Ray Dolby.

Driver or Drive Unit - Another term for a speaker.

DSP - Digital Sound or (Signal) Processor Lets you customise the sound. Could be called a super equaliser.

Dual Cone - Speakers that have two cones; the second cone is usually much smaller and stiffer and mounted on the voice-coil ahead of the main cone.

DYNAS – A new technology that guarantee’s perfect FM reception due to a higher selectivity and improved sensitivity.

Enclosure – A housing or box that holds a speaker, commonly a Subwoofer.

EON - Enhanced Other Networks. Allows you to receive traffic information from other radio stations whilst listening to the radio or CD, etc.

Factory Fit CD Changer - A Compact disc changer that is only compatible with the cars original radio. Increasing in popularity as more and more manufacturers fit stereos with CD control (able to operate a CD changer unit).

So instead of replacing the radio to fit a CD/radio or CD or MD package you can simply add-on the compatible CD changer unit and fit it in the boot.

Fader - Control that balances the front to rear sound in a four-speaker system.

Fascia Adapter - Enables a standard DIN size radio to be fitted into a vehicle that has a non-standard DIN shaped original radio fitted.

Free-Air - Term relating to subwoofers which are designed to work most efficiently in free air using the boot for example, as an enclosure. Also known as 'infinite baffle'

Frequency Response – The range of frequencies that an item of equipment is capable of reproducing.

Front End – An expression to describe the head unit or radio.

Full Range - Speakers designed to produce a wide frequency range.

Gain – Degree of signal amplification, achieved by an amp, tuner or pre-amp circuit. Expressed in decibels (dB)

GPS – Global Positioning System is a navigation system made up of a network of 24 satellites placed into orbit by the U.S. Department of Defence. GPS was originally intended for military applications, but in the 1980s, the government made the system available for civilian use. GPS works in any weather conditions, anywhere in the world, 24 hours a day. 

GPS when used to guide in-car navigation systems requires that a GPS receiver found in your car be set up on a precisely known location. The base station receiver calculates its position based on satellite signals and compares this location to the known location and the intended destination.


Graphic Equaliser – Has a number of controls, which boost and cut a band of frequencies to customise your preferred sound.

Harness Adapter Lead - Will convert your cars wiring to ISO connections. The ISO connections will then accommodate your new radio.

Head Unit – Another term for a car radio, also known as a stereo, source unit or front end.

High Pass Filter - (Capacitor) An electric circuit designed to pass high frequencies, only.

Infinite Baffle – Also known as a ‘closed box’ and meaning a speaker enclosure that is completely sealed.

Interface Adapter – In car audio terms a device that enables your factory installed radio to operate a different make of CD changer. Making them compatible.

Intro Scan - Plays the first 10 seconds of every track on a tape or CD consecutively.

ISO – (stands for International Organisation for Standardization) European standard plug-in type installation connector now used by all radio manufacturers. Having ISO specification connectors means you can replace stereos very easily.

Key-Off - Pinch roller release when cassette is not in use to prevent tape damage

Local/DX - Two levels of sensitivity for tuner searching, local and distant.

Logic Control – A term used when the functions of a tape deck are controlled by a microprocessor, which allows light ‘touch’ controls and almost guarantees safe tape handlings.

Loudness – Boosts the very high and very low frequency sounds at lower volume levels to give a natural sound balance.

Low Pass Filter – An electric circuit designed to pass only low frequencies. Used with subwoofers.

MASH - Panasonic's Multi Stage Noise Shaping - Latest Digital/Analogue technology.

MD – Mini Disc Player In-dash players are combined with a radio.

MD Changer - Mini Disc player unit that holds multiple MDs and mounts in the boot or under a seat. Usually holds 6 discs depending on the make and model. It is connected to your radio by a Bus lead, which is hidden under the carpet and operated by your radio. Can be bought individually or together with a radio as a package.

MD Changer Package

A Package comprising of a radio, Compact Disc changer unit and a connecting lead. Radio can be a cassette/radio, CD/radio, MD/radio or MP3/radio.

MDF - Medium Density Fibreboard The wood type used for making bass enclosures, door panels etc.

Midrange - A speaker designed to produce the frequencies in the middle of the sound frequency range. Typically 1000 Hz to 4000 Hz.

MOSFET – (stands for Metal-oxide-semiconductor Field Effect Transistor) A power transistor (the engine of the amplifier), that gives efficiency and high power delivery whilst delivering a wide frequency response. Thought to be so good that the manufacturers will generally print the fact on the outer casing of the amplifier. Not being a MOSFET design is not necessarily a rejection criterion, though.

MP3 Player – MP3 player and radio combined, found in the dash.

MSS - Music search system found on Denon, Philips and Radiomobile radios.

OFC – Oxygen Free Copper Refers to high quality cable that gives better sound quality.

Oversampling – A process that improves the resolution of the digital-to-analogue conversion process used in a CD player and avoids difficult design problems elsewhere in the circuitry.

Parking Sensor - Also known as a Parking Aid or Reversing Sensor, they fit onto to the rear and front bumper and provide audible tones to alert you of your proximity in relation to surrounding objects. Ultra-sonic type sensors actually mount in your bumpers and for a long time were the conventional choice, but a recent breakthrough to hit the market has taken their responsiveness and reliability to a new level and these are Electro-Magnetic type sensors that enable your bumper to remain in tact as an adhesive antenna is placed on the inner side of your bumper. 


PI - Programme Identification

PLL - Phase Locked Loop, keeps FM signals locked to their stations.

Ported – A term used in speaker box design. The air in the box is connected to the air outside via a tube called a port. Ported boxes can give good bass reproduction.

Power Caps - large canister(s) you sometimes see close to the amplifiers. It provides a relatively small store of power, which can be quickly discharged to meet amplifier peak current demands. The benefit, if the cap is correctly installed and partnered with a good battery, is a more lively sound with greater impact.

Power Fader – Controls the volume relation between the front and rear speakers connected to a built-in amplifier.

Power Loading – The system loads and ejects CD or tape automatically.

Pre-Amp - Holds controls for volume, bass and treble but has no on-board amplification.

Pre-Amp Fader - Adjusts front/rear balance at pre-amp level, used in combination with pre-outs and external amplifiers.

Pre Amp output - A pre-amp output (pre-out) on a head unit allows you to add an optional power amplifier, usually by RCA connectors.

5.5 volt pre amp output – Provides a higher dynamic range to the preamp output that improves the signal-to-noise ratio and reduces distortion.

Presets – Buttons on radios that memorise radio stations for instant recall.

Programme Selector - Tape function that allows the user to switch from one side of the tape to the other.

PS - Programme Service

PTY - Programme Type Using RDS information the unit will find a station broadcasting the type of music you wish to listen to pop, classical, news, sport, religion, etc.

QRB - Quick Release Bracket, a removable head unit.

Radar & Laser Detectors - Small device commonly mounted inside your car that monitors the road ahead and detects GATSO cameras and other speed monitoring devices to warn you of their location so you can adjust your speed accordingly. They come in many different designs and are now available with GPS technology for ultimate protection.


RCA – Connector plug with long centred terminal and shorter screening terminal. Also known as a Phono connectors.

RDS - Radio Data System FM radio frequencies contain extra information along with the music, RDS equipment reads this information and uses it to give you various features. The unit will automatically re-tune as you drive to the strongest signal for the station you are listening to. The display will tell you the station name instead of just the radio frequency. Press the right button (see EON) and the radio will interrupt your radio, CD or tape play to let you hear traffic bulletins as and when they are broadcast. You also get a clock and date.

Removable Fascia/Front Panel, T.D.F. – (Theft Deterrent Face plate) Head unit Fascias are detachable to reduce risk of theft.

Reversing Sensor - Also known as a Parking Aid or Parking Sensor, they fit onto to the rear and front bumper and provide audible tones to alert you of your proximity in relation to surrounding objects. Ultra-sonic type sensors actually mount in your bumpers and for a long time were the conventional choice, but a recent breakthrough to hit the market has taken their responsiveness and reliability to a new level and these are Electro-Magnetic type sensors that enable your bumper to remain in tact as an adhesive antenna is placed on the inner side of your bumper.


Roll Off - The point at which the frequency level and performance of a speaker diminish.

RTA - Real Time Analyser Equipment that measures frequency response and SPL level.

Satellite Navigation – Commonly known as 'SAT NAV', is an electronic device that fits in your radio aperture and acts like a co-pilot and guides you perfectly to your destination. This is achieved by timely commands, either visual from a small monitor, and/or voice from your speakers, that ensure you never miss a turn and help you arrive at your destination Stress Free.

Speed sensors in the unit are linked to your vehicles 'speedo' and with the aid of GPS (Global Positioning System) determines' the position of your vehicle. The Navigation System has a radio and CD-ROM drive incorporated and some come with a motorised pop-up monitor. The CD ROM holds the mapping information. Various manufacturers include an anti-theft removable fascia panel.

SDK – A German traffic information system.

Signal To Noise Ratio – It’s the level of background noise or hiss in a system in proportion to the power being used in an amplifier. Expressed in decibels. Higher the decibels figure the better. An excellent amplifier is 90 dB and higher.

Signal Processor – These come in the form of Crossovers, Graphic Equalisers and Digital Signal Processors. They are responsible for the manipulation of the sound frequency range.


SMART Leads – are leads with electronic solutions that allow you to interface with your car’s existing audio features. So with regards to steering wheel remote controls, the SMART leads give you the facility to operate aftermarket radios.

Speaker – An electro-acoustic device that amplifies sound. The four commonly used types of speakers are woofer, mid-range, and tweeter and subwoofer.

Subwoofer Output – Preamp output exclusively reserved for an external subwoofer amplifier.

Subwoofer - Large speakers designed to reproduce frequencies from the ultra low bass region. Because they can be felt rather than heard, they can be mounted almost anywhere in the car and are often powered in mono. Typical frequencies are (20 Hz to 150 Hz). Designed to be used in an enclosure, tube or free-air set-up.

THD – ‘Total Harmonic Distortion’ Audio signals suffer some distortion as they pass through electronic circuits. The amount of distortion can be measured expressed as a percentage. Power levels should always be referenced to a specific distortion figure. The lower the figure the better. Look for something like "50W RMS at 0.1% distortion".

TP/TA - Traffic Programme/Traffic Announcement See RDS

Track Search - Tape feature that you can rewind or fast forward to the next track and in some cases to any desired track.

Triaxial – A speaker that is composed of three individual voice coils and cones. Produces 3 segments of the audio range. Also known as a 3-Way speaker.

Tuner – Another name for a radio

Tweeter - A speaker designed to produce the higher frequencies (treble) of the sound frequency range, typically 4000 Hz to 20,000 Hz. Physically a small speaker.

Unilink - Sony bi-directional 8-pin BUS connector for centralised multi-media control from a master unit.

Woofer – A speaker designed to produce the low frequencies (bass) of the sound frequency range, typically 20 Hz to 1000 Hz.

Wow And Flutter – Audible variation in the pitch of music caused by speed instability in tape decks. ‘Wow’ refers to low speed variations, which sound like a slow "wavering" in the pitch of a note. ‘Flutter’ implies higher-speed effects, which can make a sustained note sound ‘feathery’. The lower the figure the better.

2-WAY - A speaker system made with two types of drivers (see Coaxial)

3-WAY - A speaker system made with three different types of drivers, (see Triaxial).

Technical Glossary

AM – Amplitude Modulation. One of two main ways of making a radio wave carry speech or music and used for long, medium and short-wave broadcasting in the UK. Prone to various forms of interference, which FM is not, and audio frequency response on AM is not very good.

Ampere (A) – The unit of measurement for electrical current.

Aperture – Means an opening, a hole. So in car radio terms it’s the opening in the dash that the radio sits in.

Audio Frequency – The acoustic spectrum of human hearing, generally regarded to be between 20 Hz and 20,000 Hz.

Bass - The lower end of the audio frequency spectrum, approximately 20 Hz to about 1000 Hz.

Capacitors – or ‘Power Caps’ when discussed in audio circles, generally refers to the large canister(s) you sometimes see close to the amplifiers. It provides a relatively small store of power that can be quickly discharged to meet amplifier peak current demands. The benefit, if the cap is correctly installed and partnered with a good battery, is a more lively sound with greater impact.

Clipping – A distortion that usually occurs in an amplifier when its input signal is too high or when the volume control is turned up too high.

Decibel (dB) – The dB is a unit referring to the measurement of the relative amplitude of different sound levels.

DIN E - Deutsche Industrie Norm. German standard used by most manufacturers for the measurement of the radio aperture provided. Din is also used to describe multi pin plugs used for interconnections.

Equalisation – The adjustment of frequency response to customise the sound to your personal preference.

FM – Frequency Modulation. Another way of making a radio wave transfer speech and music information. Less prone to interference than AM and makes high-quality stereo radio reproduction possible.

Ground – Commonly a cars chassis or body of car. Linked to the batteries negative terminal. 0 Voltage.

Hertz - Unit of measurement for frequency, often written as Hz or kHz

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

ISO – (stands for International Organisation for Standardization) European standard plug-in type installation connector now used by all radio manufacturers. Having ISO specification connectors means you can replace stereos very easily.

Mono – (Short for Monaural). Giving the effect of sound from a single direction, not stereophonic.

MOSFET – (stands for Metal-oxide-semiconductor Field Effect Transistor) A power transistor (the engine of the amplifier), that gives efficiency and high power delivery whilst delivering a wide frequency response. Thought to be so good that the manufacturers will generally print the fact on the outer casing of the amplifier. Not being a MOSFET design is not necessarily a rejection criterion, though.

Multipath – A form of distortion found in radios, caused by reflected signals from hills, tall buildings, etc.

Ohm – A unit of electrical resistance.

Oversampling – A process that improves the resolution of the digital-to-analogue conversion process used in a CD player and avoids difficult design problems elsewhere in the circuitry.

Phasing or Out Of Phase – Reversing the connections to one speaker in a stereo system makes their cones move in opposite directions – one ‘pushes’ while the other ‘pulls’. This causes a loss of stereo sound.

RMS - Root Mean Square, a measurement of the maximum output of an amplifier expressed in Watts. A higher figure, the more powerful the amplifier.

Separation – also called ‘crosstalk’ is a measurement indicating the amount of isolation between the channels of a stereo system, expressed in decibels. The higher the figure, the better the imaging will be.

SPL - Sound Pressure Level Loudness of an acoustic wave stated in decibels.

Staging - Where the listener perceives the origin of the music to be coming from.

Stereo – (short for stereophonic). Giving the effect of sound from different directions.

Sub Bass – Powerful Bass frequencies.

Treble – The upper end of the audio range, usually produced by a tweeter.

Voltage – Electrical pressure, produced in vehicles by a 12 Volt battery.

Watt – A unit of electrical power.