Car Audio Dictionary

 2-Car Operation
Lets one remote control operate a second alarm in a different vehicle.

2-stage Shock Sensor
Provides a warning chirp if your car is lightly bumped. A full siren blast occurs if the vehicle is hit harder.

2.4 GHz
The radio frequency range at which 802.11b, 802.11g, and Bluetooth wireless devices operate. This is also the frequency range of many household devices such as microwaves and cordless phones, which could potentially lead to interference and signal degradation.

5 GHz
The radio frequency range at which 802.11a devices operate. By using this range, devices are able to negate much of the interference that accompanies many 2.4 GHz wireless devices.


AAC
Acronym for Advanced Audio Coding, a digital music file format. AAC is a form of perceptual coding where some of the redundant parts of a digital file can be discarded to reduce file size and without noticeably degrading the sound quality. AAC is a ‘lossy’ compression format, which means that some of the file information is lost upon playback. AAC encoding is the default file format for Apple’s iTunes, ripped music (if you do not change the default preferences), as well as other digital music management programs. Any AAC music file must have a compatible playback device to play the file. Many in-dash receivers have the ability to play AAC files (along with other file formats) through playing ‘ripped’ CDs (CD-R, CD-RW) or stored digital music on a USB thumb drive.


Acoustic Suspension
A type of subwoofer enclosure design in which the subwoofer is installed in a completely sealed, specifically sized, enclosure that provides the ‘air spring’ to move the subwoofer back from its electrically extended position. The sealed volume of air provides the restoring force. The required enclosure size depends on many of the subwoofer’s electro-mechanical parameters. There is not one universal size of enclosure for every woofer. See also: Sealed, Vented, Band-Pass Enclosure.


Active Crossover
A type of crossover that is built in to in-dash receivers, amplifiers, or other preamp level signal processing devices. Active crossovers filter out unwanted frequencies not intended for a specific speaker (or group of speakers). These require external power to perform their function, usually part of other electronics within the in-dash receiver, amplifier or signal processing device. See also: Crossover and Passive Crossover. An active crossover is also referred to as an electronic crossover because it requires power and ground connections in order to do its job. It is installed between your receiver or equalizer and your amplifiers. An active crossover filters and directs the frequency bands in the low level signal before they reach the amplifiers. This saves your amps from doing unnecessary work, making your system more efficient. Active crossovers are usually adjustable, giving you more flexibility and letting you tweak the sound to meet the needs of your vehicle. They often have other features like bass boost and let you independently control the relative volume of different types of speakers.

Active Matrix Display
A type of flat-panel display in which the screen is refreshed frequently for superior resolution. The most common type of active matrix display is based on technology known as TFT (thin film transistor). TFT technology provides the best resolution of all flat-panel display techniques. The two terms are often used interchangeably.

Adaptive Frequency Hopping (AFH)
System in which devices constantly change their operating frequency to avoid interference from other devices and maintain security. Bluetooth wireless devices use AFH to secure transfers, changing frequency 1,600 times every second. When two Bluetooth devices are "paired" they change frequencies simultaneously, while unpaired devices operate on a different frequency hopping pattern.

Aftermarket
A term used to identify any parts not originally included with a vehicle at the time of production at the factory. Aftermarket automotive parts and accessories, as well as aftermarket car electronics are a popular way to add styling, performance, personalization and technology to a vehicle. See also: OEM.
 
 
Alarm
Term used to refer either to a vehicle security system, or specifically to the sounding device (either a siren or the vehicle’s horn) component of a vehicle security system.


AM (Amplitude Modulation)

The primary method for radio broadcasting until the 1960s, when FM was introduced. An AM radio signal is broadcast at a constant frequency, with slightly varying strengths that alter the length of the carrier wave. Those changes in signal power, or modulation of amplitude, contain the station's audio signal. AM stations broadcast between 535 kilohertz (KHz) and 1700 KHz. AM signals are more susceptible to atmospheric interference than FM, and are of a lower fidelity.

Ampere
The unit of measure for current or electrical "flow" through a circuit. It is commonly abbreviated as "amp" and should not be confused with the word "amplifier," which is also commonly abbreviated as "amp.

 
Amplifier
A device used in a car audio system to increase the audio signal levels and connect the increase in power to one or more speakers. Car audio amplifiers use a switching power supply to increase the vehicle supplied 12 volts to higher voltage levels. One of the benefits of an amplifier is that the increase in wattage (or power) allows speakers to produces higher quality sound at higher volume levels. This helps overcome road, wind and mechanical noises without distortion.


Analog signal

The standard method for broadcasting in AM and FM. The carrier wave is modulated in a way that mirrors the source signals. As the music gets louder, for example, an AM wave increases in power, while an FM wave moves to a higher frequency. Atmospheric can interfere with analog signals, slightly altering the content. This results in a slight hiss often heard in the background, and — in the case of electrical storms — crackle and bursts of static. The physical environment can also cause interference, creating multipath distortion.

Anti-Theft Protection
A security feature that helps prevent radio theft. There are several types of anti-theft protection currently in use:
Detachable Face - Lets you remove the control panel of your receiver easily, and take it with you when you leave the car. The stereo is useless to thieves without the faceplate, so the temptation to break in your car is greatly reduced. All but a handful of the receivers we offer come with a detachable face.
Security Code - Some stereos give you the option of setting up a security code. This is usually in addition to having a detachable faceplate. The security code is a three or four button combination, usually using the radio preset buttons, that has to be entered before the stereo will function.

Aspect ratio
The ratio between the width and height of an image or display screen. The NTSC television standard is 4:3 (1.33:1). However, most movies are made for the wide screen of a theater, and are originally displayed at the wider ratios of 1.85:1 or 2:35:1. DVD's huge data storage capacity makes it possible to include multiple versions of a movie on a single disc. It's not unusual for a DVD disc to feature a Standard (4:3) version on one side and a Widescreen version on the other. For monitors with standard 4:3 screens, movies (whether on disc or tape) must be re-formatted to either "letterbox" or "pan-and-scan." Letterboxing: The scaling of a widescreen image to fit a standard 4:3 aspect ratio TV screen by shrinking the image so that the width fits exactly. The horizontal black bars that appear above and below the image are actually recorded with the picture, so some of the picture's vertical resolution is lost when displayed. Letterboxing is much more common on DVD movies than VHS videos. Pan-and-scan: A technique for making a widescreen movie fit a standard TV's 4:3 aspect ratio by showing only selected portions of the original image. This is the standard practice on VHS videos ("formatted to fit your screen"), but is less common on DVDs.

Auto-Muting
Replaces a continuous audio alert with a single alert followed by clicking. This can preserve your sanity during extended radar encounters while continuing to notify you of the presence of radar.

Auto Zone Bypass
If a sensor is violated and remains violated or becomes defective, the brain will ignore the sensor and rearm automatically. If someone opens a door, then closes it on his way out, the system will rearm, and the violated door sensor will reset and continue to protect your vehicle. If you leave a door open by mistake, Auto Zone Bypass will ignore that trigger and arm the rest of the system.

Auxiliary (AUX) Input
The name given to any connection that allows the addition of an external source component into the vehicle’s audio and/or video system. This can be accomplished through standard RCA type A/V jacks, 3.5mm mini-jack input, or other interface devices with special (device specific) cables or other methods. An input on the face or rear of the receiver that enables you to connect a plug-and-play satellite radio tuner or portable music player (CD, MP3, or cassette) to the receiver. The input jack can be either Mini or RCA.


Auxiliary (AUX) Jack
A type of auxiliary input connector commonly found on the front panel of factory stereos. This is usually a 3.5mm stereo mini-jack connector.


AVRCP
Acronym for Audio Video Remote Control Profile for Bluetooth enabled devices. AVRCP allows for the control of one of the connected devices (such as a mobile phone) through the other connected device (such as the car stereo or steering wheel controls). Both devices must specifically support AVRCP profiles, not just be ‘Bluetooth’ devices.

AWG
American Wire Gauge (AWG) is the standard for measuring the diameter of electrical wires and cables. The smaller the AWG number, the larger the wire. Because of their high current demands, car amplifiers need large power wires to get enough energy from the battery to operate correctly. The more wattage an amplifier has, the larger the wires that power it need to be. 8-gauge and 4-gauge wires are commonly used sizes for powering car amplifiers.

A2DP
Acronym for Advanced Audio Distribution Profile for Bluetooth enabled devices. A2DP allows a device to stream 2 channels of 20Hz-20kHz audio from a source device (such as a mobile phone) to a second device (such as the car stereo). Both devices must specifically support A2DP profiles, not just be ‘Bluetooth’ devices.

Backup Battery
Powers your alarm if your main battery dies or is disabled by a thief.

Band-Pass
A characteristic of a filter for specific frequencies. A band-pass filter removes both low frequencies and high frequencies, allowing mid-range frequencies, called the ‘pass bandwidth’, to be sent to the speakers. Band pass filters can be either active or passive. See also: Crossover.


Band-Pass Enclosure
A type of subwoofer enclosure in which the subwoofer’s cone is mounted inside a primary chamber (sealed or vented), radiating sound into a secondary vented chamber. Through the vent(s), the subwoofer’s low frequencies exit the enclosure and enter the listen space of the vehicle. This is an effective design for smaller subwoofers to provide more output at a specific frequency. The trade-off is a choice between power handling and overall bandwidth (how low it can play). If a band-pass enclosure has excellent power handling at all frequencies, it will not deliver the lowest range of frequency. Conversely, if it delivers very low frequency bass notes, it will not handle as much power as a band-pass design not delivering as much low bass. See also: Sealed, Vented

Bandpass Filter
A bandpass filter combines a high-pass filter and low-pass filter, allowing a certain band of frequencies to pass while restricting the higher and lower frequencies. Bandpass filters can be fixed in frequency and bandwidth, or variable.

Bandwidth
The range of frequencies that a station is assigned to broadcast in by the FCC. Bandwidth is measured in kilohertz in the AM range, and megahertz in the FM. It's also used to identify a station's position on the radio dial. The maximum amount of information that can be transferred over a network in a given amount of time. It makes the most sense to think of bandwidth in terms of a river. Much like the water flow of a river is a function of the width of the river and number of obstacles, bandwidth is highest when there are few obstructions or and the information is all flowing the same direction. When multiple devices are connected to the network, the bandwidth is divided, depleting transfer rates and decreasing overall network reliability.

Basket
The basket, or frame, is the structural support of a speaker.

Basket (subwoofer)
The metal frame that holds all the components of a subwoofer together. The basket's rigidity and resistance to resonance help determine the sub's sound quality.

Bass Boost Circuitry
Increases the output of low frequencies. Usually centered somewhere between 40 and 90 Hz, many amps have variably controlled circuits that allow you to increase the bass level in dB increments (ie. 0-12 dB at 45Hz). Variable bass boosts allow you to adjust the center frequency, changing the character of the bass. If you do choose to boost the bass, you will then need to re-adjust the amp's gain, to compensate for the boost and prevent the amp from clipping and distorting.

Bi-amping
In bi-amping, separate amplifiers (or amp channels) drive the woofer and tweeter of a speaker. This way, both low-frequency drivers (woofers) and high-frequency drivers (tweeters) receive dedicated amplification.

Bit
A quantity of digital information and term used to describe digital audio quality. More ‘bits’ mean the recording contains more information. 16bit recordings are the standard for most CD’s and downloadable music that are sold commercially. Higher resolution 20 and 24bit recordings are available.


Bit Rate
The rate at which bits of digital music information are sampled for playback or encoding for compression. Many perceptual coding (compressed) digital file types use rates from 128kbits/second to 320kbits/second to encode digital information whereas high resolution formats such as a standard CD (linear PCM) uses 1.41Mbits/second and DVD (MPEG-2) uses 9.8Mbits/sec in digital encoding. The greater the bit rate, the greater the sound quality upon playback. The tradeoff is size of the digital file and storage space/format. Many compressed digital formats such as MP3 use variable bit rate encoding to maximize the space while preserving the sound quality attributes of the song.


Bluetooth
A wireless technology standard that allows two devices to connect to one another within a 33 foot (10 meter) range. Common applications of Bluetooth in a vehicle include connecting mobile phones to a compatible Bluetooth in-dash receiver or dedicated Bluetooth hands-free devices to support placing and receiving calls. There are also applications of Bluetooth that supports streaming audio and controlling the functionality of another connected Bluetooth phone or device. See also AVRCP, A2DP HFP and PBAP. A short-range, wireless technology that allows devices to connect to one another and transfer information. Up to eight devices can connect to the same network (also called a piconet), and an ad-hoc Bluetooth network has a range of about 30 feet. Current Bluetooth wireless technology-enabled devices operate in the 2.4 GHz radio frequency range, but future versions will operate in the 6-9 GHz range, eliminating the concern of interference from other wireless devices.


Box
A term commonly used to describe a subwoofer enclosure or subwoofer box. See also: Enclosure.

Box volume
This measurement, listed with each component subwoofer, tells you the recommended interior volume in cubic feet that an enclosure should have to get the best performance from the sub. A variation of 10-20 percent is generally acceptable.

Bridged Power
When you bridge an amplifier, you combine the power output of two channels into one channel. Bridging allows you to drive one speaker with more power than the amp could produce for two of the same speakers. Because of this high power output, bridging is an ideal way to drive a single subwoofer. If your amp is bridgeable, the owner's manual will have directions that tell you how. Usually, an amp is bridged by connecting the speaker leads to the positive (+) terminal from one channel and the negative (-) terminal from the other channel. However, you should be sure to consult your owner's manual before attempting to bridge your amp. Also, keep in mind that most amplifiers need to see a 4-ohm load when bridged to mono operation. If you want to bridge your amp, you should use one 4-ohm speaker or, if you prefer multiple woofers, wire two 8-ohm speakers in parallel. (Again, consult your manual before operating your amp in bridged mode.)

Built-in Crossovers
Crossovers consist of both a high-pass and low-pass filter. Often used to keep high-frequencies from reaching a subwoofer, a low-pass filter allows only frequencies below the crossover point to be amplified. A high-pass filter allows only frequencies above the crossover point to be amplified — useful for keeping low bass away from small speakers, so they can play more efficiently. Crossovers are usually listed as variable or selectable. Continuously Variable means the crossover can be freely adjusted to any frequency between the listed end points. Selectable means that you can choose from several preset crossover points.

Butyl Rubber
A rubber/butylene compound with excellent flexibility and durability. Used for speaker surrounds.

Capacitor
A capacitor, or cap, placed in series with a speaker acts as a high-pass filter, allowing only frequencies above the crossover point to pass through. A capacitor is an electronic component that stores and releases electrical charge. Heavy-duty capacitors are often used as a buffer zone between your amp and your car's electrical system to prevent the car's lights from dimming during loud playback. They store up a reservoir of power, which can supply the amplifier's peak demands (like a kick drum beat) without having to get additional current from the battery. All amplifiers have built-in capacitors, though high-performance amps use larger, more effective ones. External capacitors connect to the power cable just before it reaches your amplifier.

Cast aluminum
Cast metals have a greater resistance to resonance than stamped metals when used in speaker baskets. Cast aluminum combines light weight with rigidity and strength.

CD Text
Some compact discs contain encoded text data that can include the artist name, disc name, and/or track name. Text-capable receivers can decode and display this information on the readout.

CD-R, CD-RW Compatibility
CD receivers with this capability can play audio CD-Rs and/or CD-RWs as well as prerecorded CDs. Almost all of today's receivers can play CD-R and CD-RW discs.

CEA-2006 Compliant
On May 28, 2003, the Consumer Electronics Association published standard CEA-2006, "Testing & Measurement Methods for Mobile Audio Amplifiers." This "voluntary" standard advocates a uniform method for determining an amplifier's RMS power and signal-to-noise ratio. Using 14.4 volts, RMS watts are measured into a 4-ohm impedance load at 1 percent Total Harmonic Distortion (THD) plus noise, at a frequency range (for general purpose amplifiers) of 20 Hz to 20,000 Hz. Signal-to-Noise ratio is measured in weighted absolute decibels (dBA) at a reference of 1 watt into 4 ohms. This applies to both external amplifiers and the amplifiers within in-dash receivers. CEA-2006 allows consumers to be able to compare car amplifiers and receivers on an equal basis. Manufacturers who choose to abide by the new standard are able to stamp their products with the CEA-2006 logo that reads: "Amp Power Standard CEA-2006 Compliant."

CEA-2006
A voluntary standard of reference established by the Consumer Electronics Association (CEA) for rating and reporting the power output of aftermarket car audio electronics. CEA-2006 covers both ‘built in’ power of receivers and dedicated power amplifiers, which have power output greater than 5 watts. The current version of CEA-2006 is revision ‘B’ (CEA-2006B) in which the latest classes of full range switching amplifiers are included in the test and measurement procedures. This standard is intended to compliment CEA-2031 which describes the amount of power speakers with the certain rating can reliably handle. While not all companies report their power outputs as CEA-2006 compliant, if you wish to compare two or more products this is the most reliable way to do so.


CEA-2015
A voluntary standard of reference established by the Consumer Electronics Association (CEA) for wires and cables used in aftermarket car electronics installations involving power wiring or speaker wiring. CEA-2015 standards are reported on many manufacturer’s amplifier and speaker wiring kits (or individual cable assemblies) and are intended to help match the wiring size and current capacity requirements with the CEA-2006 amplifier power output standards. By choosing a CEA-2015 compliant power and speaker cable, you provide the highest probability that the CEA-2006 rated amplifier will be able to deliver its full rated power.


CEA-2031
A voluntary standard of reference established by the Consumer Electronics Association (CEA) for rating and reporting the power handling of aftermarket car audio speakers. In addition to voluntarily reporting power handling, manufacturers who participate in the CEA-2031 standard also report the cutout diameter, mounting depth (to ensure proper fit), the impedance, and several other attributes that allow consumers to compare different speakers and easy match them with a CEA-2006 labeled amplifier power output.


Chassis Ground
The electrical return path of the vehicle’s DC electrical circuits using the conductive metal body and/or frame of the vehicle. Think it of it as one large wire connecting the negative battery post with the negative side of circuits in the vehicle. One caution is that many vehicles use composites, thin metal, or advanced adhesives, which may not necessarily make an electrically suitable chassis ground connection. This is especially true for devices with large current requirements such as amplifiers and auxiliary lighting.


Clipping
An undesirable effect on the audio signal introduced by an incorrectly matched output signal and input capacity of two analog audio devices (or where no level matching control exists, simply incompatible devices). Clipping produces audible distortion in music, but also increases the amount of energy in the signal and transfers that energy as heat into the voice coils of speakers. Clipping can be the cause of premature speaker failure if it’s introducing more energy (power) than the speaker is intended to handle continuously. See also: Gain, Input Sensitivity. Clipping occurs when an audio circuit's maximum capacity is exceded. The circuit won't reproduce the excessive parts of the signal, "clipping off" the round tops and bottoms of the musical waveforms, leaving them square, and introducing a huge amount of distortion into the output signal. Clipping can be heard as a crunching sound on musical peaks. A clipped signal, especially one that has been amplified, can be very destructive to your speakers and subs.

Coaxial speaker
Coaxial speakers contain two elements: a woofer, to reproduce the low notes, and a tweeter, mounted inside the woofer, for the highs. See also "Two-Way Speakers", below.

Codec
A codec is a method of compressing and decompressing digitized sound. MP3 and WMA are examples of different codecs. In the standard CD audio format, one minute of music takes up roughly 10 megabytes. When converted to MP3, that same minute of music takes up only about 1 megabyte.

Coil
A coil, or inductor, placed in series with a speaker acts as a low-pass filter, allowing only frequencies below the crossover point to pass through.

Component System
Component systems, or separates, use a superior speaker design to give you the best possible sound. A typical separates system includes 2 woofers, 2 tweeters, and 2 external crossovers — all of which are designed to work smoothly with one another. Generally, components are made of better materials than their two- or three-way counterparts. You can position the separate tweeters for optimal imaging. Given adequate power, separates deliver exceptional dynamics and detail.

Composite Video Output
A video signal in which the brightness and color portions of the signal are combined. A standard RCA-type video jack provides a composite video signal.

Crossover
A filter network, either active or passive, that only allows certain frequencies to pass through to a speaker and to be played. The crossover point is the frequency at which the cutoff occurs and the type of crossover (high pass or low pass) determines whether the frequencies above or below that point will pass or be filtered out. The ‘slope’ or ‘roll-off’ determines the amount of filtering as frequencies increase (in a low pass) or decrease (in a high pass). A crossover with two filter points, one on the high side of the frequency spectrum and one on the low side, is known as a band-pass filter. See also: Active Crossover and Passive Crossover.

Crossover (High-Pass Filter)
A built-in high-pass filter allows only frequencies above the crossover point to pass through. This filter may work with the speaker outputs, preamp outputs, or both.

Crossover (Low-Pass Filter)
A built-in low-pass filter allows only low frequencies to pass through. This filter may work with the speaker outputs (very rare), preamp outputs, or both.

Crossover Point
In high-pass filters, low-pass filters, and crossovers, the crossover point is the frequency at which the level of the output signal has been reduced by 3 dB.

Crossover Slope
The rate at which the crossover attenuates the blocked frequencies. Slope is expressed as decibels per octave. A 6dB per octave crossover reduces signal level by 6dB in every octave starting at the crossover point. This means that every time the frequency of the audio signal is changed by a factor of 2 (one octave), the level of the audio signal will change by 6dB. For example, if your low-pass filter is set at 80Hz with a 6dB slope, you'll see a drop in level of 6dB at 160Hz. With slopes of 12dB and higher, you'll hear little output beyond the crossover point.

DAC, Digital-to-Analog (D/A) Converter
Your CD receiver uses a D/A converter to convert digital 1s and 0s back into analog audio signals. CDs store audio data in binary, digital form. This digital data is an accurate, noise-free reproduction of recorded signals, but in digital form it doesn't sound like music to your ears. The D/A converter translates the digital info back into music — that's why it's so important to your CD receiver's performance.

Damping
Adding mass or resistive force to an object to control resonance. In car audio, damping is commonly done with adhesive sheet based materials attached to sheet metal and plastic panels in the vehicle to reduce noise and vibration. Reducing noise in the vehicle also makes the audio system have to work less to achieve a certain volume level. This word is commonly misused as ‘dampening’, which is not correct. Dampening is making something wet. Damping is controlling resonance. See also: dB

Damping Factor
Damping is the ability of a amplifier to stop the speaker cone from continuing to vibrate after the signal stops. A system with good damping plays sound cleanly with no hint of unintentional echoes or reverberations. The higher the damping factor, the greater the accuracy. The ability of an amplifier to control the movement of a subwoofer — the higher the damping factor, the greater the accuracy. Damping factor is calculated by dividing the subwoofer impedance by the output impedance of the amplifier. An amplifier's damping factor will decrease as the sub's impedance decreases — that's why an amp running at 4 ohms will provide tighter bass than at 2 ohms. This spec is not always given for all amplifiers.

Data Compression
Data compression (or data reduction) reduces the information in a digital music file by removing non-essential data, reducing the size of the file by as much as 15 to one. The process makes it possible for satellite radio providers to store, transfer, and broadcast huge quantities of musical information.

dB (Decibel)
An acronym for Decibel. Decibels are a way to express ratios of increase or decreases in electrical signals or, as they’re commonly used, in sound pressure levels (SPL). When a sound increases +3dB SPL, that’s about the lowest amount of perceivable difference when music is playing. To achieve that +3dB increase in SPL (changing nothing else in a system) requires about twice the amount of power to achieve. Thus, if you can only hear a slight increase and it takes twice the amount of power to achieve it, don’t worry about whether an amplifier is rated to produce 85 watts/channel or 95 watts/channel because, literally, you really wouldn’t hear the difference. Just for reference an increase of +10dB of SPL requires 10 times of an increase in power, so the best ways to achieve increases in SPL are often to help make the car itself quieter. See also: Damping.


DC Resistance (DCR)
In speakers, the DC resistance is the measured resistance of the speaker’s voice coil. This is not the same as impedance or nominal impedance. The nominal impedance is an average that reflects a close match of the DC resistance with common values like ‘4-ohms’ or ‘2-ohms’ so that multiple speakers or voice coils can be wired together with a predictable value that matches to an amplifier’s recommended load. See also: Impedance, Nominal Impedance.

Diaphragm
A speaker diaphragm is the surface that radiates sound. For a woofer, this is the speaker cone. In a tweeter, it's usually dome-shaped.

Digital Audio Broadcasting
A radio wave comprised of digital information that is decoded by a compatible radio receiver into sound. Because the receivers read only the digital code, and ignore fluxuations in either the amplitude and frequency of the carrier wave, content is unaffected by atmospheric conditions, or subject to multipath distortion.

Digital Media Files
Music which has been subjected to data compression — allowing users to store many hours of music as computer files. A growing number of in-dash CD receivers have the ability to decode and play recordable CDs (CD-Rs and CD-RWs) loaded with MP3, WMA, AAC, or WAV files. A single disc can hold up to ten hours of music.

Digital Media Receiver
Digital media receivers are in-dash receivers that do not have CD players built in. Instead, they feature multiple inputs for devices like iPods, USB drives, SD cards, and so on.

Digital Crossover
A digital crossover does all its filtering in the digital domain, and displays all your options on a menu screen. A digital crossover offers two advantages over the analog version. First, you can set your filters much more precisely, and you'll find much greater flexibility in setting up a complex system. Second, you can store different crossover settings in memory locations, and recall them with the touch of a button — that's a big plus if you're comparing settings or switching settings for a car audio competition.

Digital Output
Most DVD players and some DVD receivers include at least one digital audio output for sending the Dolby Digital or DTS bitstream to a compatible decoder. Digital data transfer offers extremely wide bandwidth, immunity to radio frequency (RF) interference, and an easy one-cable connection. The two most common types of digital output are coaxial and optical. Both types require a special cable to connect to the digital input of a Dolby Digital/DTS-equipped surround processor.

Digital Theater Systems (DTS)
DTS is an established multichannel audio format in movie theaters. Like Dolby Digital, DTS is primarily a 5.1-channel format. The compression scheme used in DTS "throws away" significantly less audio data than Dolby Digital, so it should sound better, but so far, side-by-side comparisons have been inconclusive. Nearly all new DVD players are DTS-compatible; many in-dash receivers and most surround processors include DTS decoding. Still, the number and availability of DVD titles with DTS soundtracks remains somewhat limited.

Digital-to-Analog Converter (DAC)
A component necessary in any source unit that plays digital music sources, but must output analog audio signals. Nearly all in-dash CD and DVD head units have a DAC to convert the ones and zeros of digital music to either preamp RCA outputs or speaker level outputs through the head unit’s built in amplifier. Even your portable media device has a DAC if you store audio files and play them back through a headphone jack. Many high end head units use a higher quality internal DAC to convert digital audio from a portable device to analog audio outputs when connected by their special cable assemblies.


DIN
An acronym that describes the internationally standardized size of an in-dash receiver in aftermarket car audio. The physical dash opening dimensions of a DIN receiver are roughly 2” high x 7” wide. There is not a standardized depth for DIN receivers. The front panel of a DIN receiver is typically smaller than the dash panel opening and has a trim ring to cosmetically finish out any gaps.
 
 
DJ Mixer
A DJ mixer is a type of audio mixing console used by disc jockeys. DJs playing music for dancers at a club use the mixer to make smooth transitions between different songs which are played on sound sources that are plugged into the mixer. These sound sources could be turntables, CD players, or iPods.
 
 
DJ Controller
MIDI controllers or USB-to-analog devices used for controlling computer-based DJ software, installed on a personal computer, laptop, or tablet device.

Double-DIN
The terminology describing a standardized ‘double height’ head unit in aftermarket car audio. The physical dash opening dimensions of a Double-DIN head unit are roughly 4” high x 7” wide. There is not a standardized depth for Double-DIN head units. The actual front panel of a Double-DIN head unit is usually smaller than the opening and has a trim ring to cosmetically finish out any gaps in the opening depending on how it’s installed. Double-DIN head units often have large display screens and are common with in-dash navigation and DVD player units.

Dock & Play Satellite Radio
A Dock & Play satellite radio tuner can be transferred from car to home, simply by plugging the tuner into a docking station in either location. A Dock & Play tuner has its own controls and line output, so it can be connected to any receiver with an auxiliary input.

Docking Station
A docking station is a cradle with an adjustable stand which can be installed in any location (car or home). The tuner can be transported easily from one permanently mounted docking station to another.

DSP
Digital Signal Processing. The technology in car audio that allows the audio signal to be processed with high speed and accuracy in the digital domain where numerous levels of functionality can be realized for low cost and in a small equipment size. DSP technology is found in many aftermarket head units, in signal processors and many other types of consumer electronic devices. DSP devices that are part of an analog audio signal path must also use digital-to-analog converters (DAC) to convert any audio processing back to analog form to continue in the audio signal path.

Dual Cone
A dual cone speaker uses an inexpensive design in which a small "whizzer" cone attached to the center of the woofer reproduces the high frequencies.

Dual voice coil subwoofer
While typical speaker drivers have one voice coil, dual voice coil (DVC) subwoofers allow you the advantage of flexibility in wiring your system. Parallel wiring provides for maximum amplifier output, while series wiring lets you configure multiple woofers to one amplifier at an acceptable impedance. In series/parallel mode, you can wire 4 woofers to a single amp, for example, and still maintain a compatible impedance. Independent wiring lets you drive a single sub without bridging (or by bridging a four channel amp to one sub).

Dust cap
A dust cap covers the center of a speaker's cone and keeps dirt out of the voice coil gap.

DVD Receivers
These versatile receivers can play DVD movies, and may play DVD audio discs. Some models send the video signal to an outboard backseat monitor for on-the-go viewing, while other models include a built-in screen for stationary viewing. These receivers have digital-to-analog converters that are superior to those found in most regular CD receivers, so your CDs will usually sound better on a DVD receiver.

Efficiency
Although a speaker's efficiency rating is almost always correlated to its sensitivity rating, it's actually a different measurement. The efficiency rating for a speaker measures how well a speaker converts watts of electrical power into watts of acoustical power. Most speakers have a very low efficiency rating — between 1% and 10% — so manufacturers rarely provide this information, choosing instead to list sensitivity ratings.

Enclosure
A subwoofer enclosure is an enclosed space in which the subwoofer is installed to achieve low bass response. Commonly called a ‘subwoofer box’, the enclosure’s job is to provide a specific amount of air space to the subwoofer for restoring force of the cone, sort of like an air spring. Subwoofer enclosures can be made from dense wood such as Medium Density Fiberboard (MDF), marine grade plywood or other composites such as fiberglass or roto-molded plastics. The shape of the enclosure is not nearly important as the airspace inside of it. As long as the structure is rigid and does not flex when the subwoofer plays, the shape then only becomes important to fit in to the space where you can safely and conveniently install the subwoofer enclosure. The most common types of subwoofer enclosures used in car audio are sealed, vented and band-pass designs. See also: Sealed, Vented, Band-Pass Enclosure.

Sealed box — A sealed box is an airtight enclosure housing your subwoofer. A sealed box is best for any music that demands tight, accurate bass. Expect flat response, deep bass extension, and excellent power handling. Since a sealed enclosure tends to require more power than a ported box, use an amplifier with ample wattage for optimum performance.
Ported box — A ported box uses a vent (called a port) which allows movement of air in and out of the enclosure chamber. This additional air movement reinforces low bass response. You get more output from a ported box than you would from a sealed box at any given level of amplifier output. Some people simply prefer the sound of ported boxes for rap, techno, or any hard-driving music because they play louder than comparable sealed boxes.
Bandpass box — A bandpass box is a special type of ported box designed for maximum slam. The woofer is mounted inside a dual-chambered box; the woofer fires from the sealed chamber into the ported chamber, and sound waves emerge from the ported side. Because the sound that comes out of the port is extra loud within a narrow frequency range, bandpass boxes are considered super efficient. Their aggressive sound is popular with many hip-hop, techno, and metal fans.
Free-air subwoofers — A free-air system consists of woofers mounted to a board attached to the rear deck or placed in the trunk against the rear seat. The trunk acts as the enclosure housing the subwoofer. Free-air systems save space and have flat frequency response. The woofer must be specifically designed for free-air use, and the trunk must be airtight for best results.

Encryption
The process of obscuring information to make it unreadable without special knowledge. Encryption is used in wireless technology to ensure the secrecy of the information contained on the network. Bluetooth wireless technology uses adaptive frequency hopping as its form of encryption, while Wi-Fi networks require the administrator to set up the security. WPA2 is the most widely used and reliable form of encryption for personal Wi-Fi networks.

Equalizer
A device that is able to adjust the sound at one or more points in the audible sound spectrum. Many equalizers have fixed band adjustments at specific frequencies and others have adjustable frequency bands to customize the sound adjustment even more. Most equalizers in car audio are preamp level equalizers that go in the signal path after a head unit and before amplifiers, but there are also ‘built-in’ equalizers in both head units and in some amplifiers. When an equalizer is built-in, it generally has very limited adjustment capability compared to an outboard preamp level equalizer. A built-in EQ lets you tailor the sound to your listening tastes and to your vehicle's acoustics. Receivers with built-in EQs will have one or more equalizer "bands" in addition to standard bass and treble controls. These equalizer "bands" usually have fixed center frequencies and bandwidths (although some may be adjustable). More sophisticated built-in EQs offer parametric equalization, which allows you to set the amount (in dB) by which a certain frequency band is boosted or cut — and determine the width and/or center frequency of this band. This gives you extremely precise control of the tonal balance in your vehicle.

Feedback
Feedback is when an electronic circuit's output signal is used to modify its own input. This is handy in getting rid of noise, for example, by subtracting any signal differences.

Filter Network
Another name for a crossover, either passive or active. Technically, there are other types of filter networks in addition to crossovers, but they are not often found commercially. Instead they are custom built. Example a crossover (filter): This tweeter comes with a passive high-pass filter network.

FireWire (IEEE 1394 or i.Link)
Wired connection (serial bus) standard similar to, but faster than, USB. FireWire was originally developed by Apple Computers as a computer connection standard, but many devices (namely digital camcorders) feature FireWire ports beacuse of their high data transfer rates.

FM (Frequency Modulation)
A radio signal broadcast at a constant amplitude, with slight variations in frequency. These frequency differences carry the station's audio signal. FM stations broadcast between 88 megaherz (MHz) and 108 MHz. Because the strength (or amplitude) of the FM signal is constant, they are less susceptible to atmospheric interference than AM signals. It also allows the FM signal to carry more information. Most stations prefer to broadcast music in FM as it sounds fuller, and more readily allows for stereo separation.

Foamed IMPP
When polypropylene is injected as a foam into a speaker mold, the resulting material retains air bubbles that make it lighter without giving up strength.

Frequency Range
The range of sounds from lowest to highest that the subwoofer is capable of reproducing. The figures listed with the drivers are furnished by the manufacturers. The actual range you'll hear can vary depending upon the type of box, crossover point, and the vehicle the subwoofer is installed in. Under most circumstances, a typical sub will play slightly deeper than its published figures indicate. So, don't base your choice solely on this spec.

Frequency Response
A term that describes the overall range of a particular audio signal, piece of audio equipment or performance of an entire audio system. The human hearing range is accepted to be 20Hz-20,000Hz (abbreviated 20-20kHz) and an earmark of a very good car audio system is one that has the ability to reproduce 20-20kHz with very little variance between those frequencies. 20Hz is very low (almost inaudible) bass frequencies and 20kHz is very high in the frequency range, also almost inaudible for many people. Although the ideal sound and balance of frequencies is unique for each listener’s preference, having a full range capability of 20-20kHz frequency response allows a system to have all the necessary capacity to be fine-tuned for just about any listener’s final preference. The range of frequencies the speaker will reproduce (lowest frequency to the highest). The optimal range is 20-20,000 Hz, the range of human hearing. Many high-quality tweeters, however, are able to reproduce frequencies well above 20,000 Hz. While the human ear can't detect these ultra-high frequencies, they do contain harmonics that affect the way listeners perceive sound and its nuances.

Full-range Speakers
Full-range speakers accurately reproduce your music's frequency range by mounting a tweeter inside the woofer cone. This is also known as a coaxial, or 2-way speaker. Some versions may add midranges or supertweeters to better reproduce other parts of the frequency spectrum. These are also referred to by the number of drivers (3-way, 4-way, etc.).

Gain
Gain, as it applies to car amplifiers, refers to the adjustment necessary to match an amplifier's input to the receiver's output. Properly setting the gain prevents an amp from "clipping," distorting the signal due to being overdriven, which can damage speakers.

Gain Control
A level matching control on most preamp level signal processors and amplifiers that is intended to match that device’s input stage to the signal levels of the analog audio signal of the preamp outputs from the previous device in the signal chain. The gain control is not a volume control. The volume of the audio system should be controlled from the head unit (or in-dash signal processor) and the level matching on the preamp level devices and amplifier(s) should be set to allow the head unit to achieve maximum volume before any audible distortion is heard. Distortion of the audio signal by inaccurate adjustment of the gain introduces an undesirable condition called clipping. See also: Clipping, Input Sensitivity.


Global Positioning System (GPS)
A constellation of 24 satellites orbiting the earth in six orbital planes giving 24/7 coverage anywhere on earth. They send unique signals to GPS compatible receivers that, when connecting to 3 or more of the satellites, can pinpoint latitude and longitude location within about 30 feet of the receiver’s location. With a fourth satellite signal, the GPS receiver can also accurately compute elevation. The GPS system was developed (and is maintained) by the US Government, though the signals are available to all GPS compatible consumer devices.

GPS
GPS, which stands for Global Positioning System, is a navigational system designed and operated by the U. S. Department of Defense (DOD). Coded satellite signals from three or more GPS satellites are processed by your vehicle's navigation computer every second, which then calculates the vehicle's velocity and geographical location.

Graphical User Interface (GUI)
An onscreen system (including menus, maps, etc.) to control a mobile audio/video system. The user employs touch controls or cursors on the monitor to navigate through system functions and parameters.

Ground
A commonly used term for chassis ground, which is the electrical return path of the vehicle’s DC electrical circuits. The conductive metal body and/or frame of the vehicle is often used for the ground path. Think it of it as one large wire connecting the negative battery post with the negative side of circuits in the vehicle. One caution is that with modern vehicle manufacturing techniques using composites, thinner metal and advanced adhesives, where metal exists in a vehicle may not necessarily make it electrically suitable for a chassis ground connection. This is especially true for devices with large current requirements such as amplifiers and auxiliary lighting.

Ground Loop
A ground loop occurs when any piece of equipment or any incoming wire is connected to a different ground or grounds. If your in-dash receiver and amplifier are grounded to different locations, for example, a ground loop may occur. In this situation, the multiple ground paths can, in effect, act as an antenna for interference. The interference is turned into noise, and you hear it in your system.

Gyroscope
Navigation systems use an internal gyroscope to track the turns a vehicle makes, which helps the system determine the direction in which a vehicle is traveling.

Harmonic Distortion
The effect of the equipment (head unit, amplifiers, speakers, etc.) on the original audio signal during playback that adds undesirable effects to the quality and realism of the music. While all music has inherent harmonics, it does not all inherently have distortion. It’s that distortion of the harmonics that make listeners uncomfortable, cringe and fatigue from listening at mid-high volume levels. Often car audio systems with poorly adjusted level matching between components suffer from unnecessary harmonic distortion.


Harmonics
In music, harmonics are both good and bad parts of the playback and listening experience. When music is recorded, harmonics are present in the original recording because of the physical space, instruments and even the uniqueness of each singer’s vocals. Those are good harmonics. Bad harmonics are anything that is added to that original recording that degrades the quality of the listening experience to make it seem less real and less like the original detail present at the time of recording. Often these bad harmonics are a result of the products through which the music is playing (introducing harmonic distortion). Speakers actually introduce the most harmonic distortion because, in a car, the ongoing challenge is always that the space is never as ideal as the original studio where the music was recorded.

HD Radio
iBiquity Digital Corporation's trademarked name for digital audio broadcasting. Although often misused, the term "HD Radio" is a trademarked brand name and does not stand for "High Definition Radio."

Head Unit
Often called a ‘stereo’ or a ‘deck’, the head unit is the in-dash source unit that controls the system volume, various music sources as well as where the display of the information is found. It’s the head of the audio system, hence the name head unit. Most aftermarket head units are available in two popular sizes, DIN or Double-DIN. When they are not a direct-fit replacement, the head unit may require a dash kit to complete the installation in cars with more complex dashboards. See also DIN and Double-DIN.

Heatsink
A heatsink is a metal structure used in electronics to draw heat away from critical components and dissipate it into the air, usually via cooling fins.

HFP
The Hands Free Profile for Bluetooth enabled devices. Allows placing and receiving of calls between a mobile phone and the hands-free device (such as the car stereo). Both devices must support HFP profiles, not just be ‘Bluetooth’ devices. True HFP also supports PBAP which allows the phone’s contacts to be viewed and accessed on the hands-free device in the car.


High Level Inputs
The Hands Free Profile for Bluetooth enabled devices. Allows placing and receiving of calls between a mobile phone and the hands-free device (such as the car stereo). Both devices must support HFP profiles, not just be ‘Bluetooth’ devices. True HFP also supports PBAP which allows the phone’s contacts to be viewed and accessed on the hands-free device in the car.


High Level Outputs
Another term used to describe speaker level outputs, usually on a head unit that contains both preamp level outputs and speaker level outputs so the two types are differentiated.


High Pass
A high-pass filter allows "high" frequencies to be sent to the speakers, while it blocks frequencies below the crossover point. A filter type where only the frequencies above the filter point are allowed to pass. High pass filters (also called low pass crossovers) can be active or passive. See also: Crossover.

IEEE 802.11
The official name for the Wi-Fi wireless specification. It is comprised of more than 20 different standards (802.11a, 802.11b, etc.), each of which have their own defining characteristics. Since not all standards operate on the same frequency, not all 802.11 devices are compliant with one another, so be sure to consider the compatibility when making your purchasing decision.

IEEE 802.15.1
The official name for the Bluetooth wireless specification.

Impedance
A measurement of dynamic resistance occurring at a specific frequency, commonly described in speakers and measured in units of ohms. Actual impedance would reflect the resistance of a speaker’s voice coil with a frequency and, over a range of frequencies, that impedance value changes to plot an impedance curve with one or more peaks (not just a flat line). Most speakers are rated at a nominal impedance value, which is an average impedance that better represents a flat line and is easier to match amplifier power ratings and amplifier operational loads. Example: “A speaker with a 4-ohm nominal impedance would connect to an amplifier that has a rated power delivered into a 4-ohm load.” Impedance is a measure of the resistance of a speaker's voice coil to the audio current supplied by the amplifier. The total opposition to the flow of alternating current in an electrical circuit at a given frequency. Impedance is measured in Ohms. Although car audio manufacturers label the impedance of most car speakers and subs at 4-ohms, the impedance of a speaker is actually not a constant. It's actual impedance changes with frequency and can vary greatly. Therefore, though 4-ohms is the standard impedance in car audio, this standard is more of an average impedance for speakers and amplifiers when driven within the part of the audio spectrum for which they are designed. See also: DC Resistance (DCR), Impedance.

IMPP (injection-molded polypropylene)
IMPP consists of polypropylene that is injected into a mold when forming the speaker cone. The speaker cone retains more stiffness, and is less colored by resonation, than cast polypropylene cones.

IMPP composite
To increase the strength and stiffness of IMPP, other materials are added to form IMPP composites. These materials are usually minerals like mica or carbon.

Infinite Baffle
A type of subwoofer mounting in which there is no enclosure except for the open space behind (and in front) of the subwoofer cone, each separated by the baffle on which the subwoofer is mounted. Traditional infinite baffle designs are found in many OEM audio systems that utilize a factory installed subwoofer in the rear deck and uses the separation between trunk and interior as the individual air spaces. Performance in low bass of infinite baffle applications is somewhat limited when compared to subwoofers of the same diameter installed in sealed or vented enclosure designs. See also: Sealed, Vented, Band-Pass Enclosure.

Inline Crossovers
Inline crossovers are a hybrid design. They are considered to be passive crossovers because they are not adjustable — they are set at a particular frequency. But they work just like an active crossover — they modify a preamp level signal, plugging into your amp's preamp inputs and setting up the frequency roadblock before the amp. The patch cord from your receiver plugs into the other side of this kind of crossover. Since they act as active crossovers, they make your system more efficient than passive crossovers. But, like passive crossovers, installation is simple and they are relatively inexpensive.

Input Sensitivity
Another term used to describe input signal level controls (or ‘gain controls’) on an amplifier or preamp level signal processor. The input sensitivity specifically refers to the range of that control, from the lowest signal voltage input to the highest (Example: 500mV-6V of signal). The input sensitivity control would then be set to a position that represents a match with the output signal voltage of the preceding device, such as the head unit’s preamp level output signal voltage. Distortion of the audio signal by inaccurate adjustment of the input signal level if set too sensitive (for a lower voltage than is actually delivered) introduces an undesirable condition called clipping. See also: Clipping, Gain.

iTunes Tagging
A process that lets you select the song you're listening to for purchase at a later time. iTunes tagging requires a docking iPod; an audio/video component that includes an HD Radio tuner, iPod dock and "Tag" button; and a tagging-enabled HD Radio signal. When you hear a song you like, press the "Tag" button, and the component will store the song information (but not the song) in its memory. When you dock your iPod to the component, it will transfer all your saved tags to the iPod. The next time you sync your iPod to your computer, the tagged songs will appear as a list in iTunes. They then can be purchased through the iTunes store. You can also tag songs directly through the tuner in a 5th generation iPod nano.

ISO-DIN
A mounting configuration where a DIN head unit is mounted to brackets and bolted into the dashboard, then the dash panel is placed over the unit so that the face of the head unit comes through the opening. This is the opposite of installations where the head unit goes into the opening from the front (called front loading) and locks into a DIN mounting chassis.


Joule
A unit of electrical energy measured over a very brief time. One joule is equal to one amp of current through a resistance of one ohm (total of one watt of ‘work’) for one second of time. In car electronics, joules are sometimes used to describe the threshold of circuit protection devices like surge protection, fuses and circuit breakers.

K-Band
The most frequently used radar frequency band: 24.05 - 24.25 GHz. K-band made its appearance in 1978. The first K-band hand-held radar guns could only be used from a stationary position. Later, a "pulsed" version was introduced that could be used from a stationary or moving vehicle. K-band radar waves have a relatively small wavelength. At the power level found in police radar guns, K-band has an effective clocking range of about 1/4 mile. Depending upon terrain (around a corner, over a hill, etc.), K-band waves can be detected from a range of 1/4 mile to 2 miles.

Ka-Band
In 1987 the FCC allocated a frequency on yet another band, Ka, for police radar use. Ka-Band incorporates Ka-band, Ka Wide-Band, and Ka Super Wide-Band. With Ka came the introduction of photo radar (also known as "photo-cop"). The photo-cop system works at 34.3 GHz and combines a Ka-band radar gun with an automated camera (see Photo Radar below). The FCC later expanded Ka-band radar use to a range of 34.2 to 35.2 GHz. This became known as Ka Wide-Band. The introduction of the "stalker" radar gun raised the stakes in the detection game. Unlike all previous guns, the Stalker can be FCC licensed for any frequency in the Ka-band between 33.4 GHz to 36.0 GHz, and so cannot be picked up by detectors designed only for X, K, and photo radar. Stalker guns are being used in more than half the country. In response, manufacturers have developed detectors with "Super wide-band" technology that sweeps all of the Ka-band allocated to radar, as well as providing continued protection against X, K, and photo radar.

Ku-Band
Ku-band radar ranges between 12 and 18 GHz. It is used primarily for satellite communications, in both aerospace and broadcasting. It is used primarily in Europe and not seen much in America. In the radar enforcement realm, Ku is set at 13.45 GHz by the FCC and has only recently been introduced to the U.S. for speed detection.

Kevlar
Kevlar is the trademarked name of a synthetic fiber developed by DuPont as a substitute for steel in tires. Also used in body armor, Kevlar, blended with other polymers, is used in speaker cones for its light weight, strength, and rigidity.

Keyless Entry
A system that uses RF commands from a keychain remote to lock and unlock the doors remotely. This feature has become standard on many vehicles, however because it involves a keychain remote some people confuse keyless entry functions with a car alarm. See also: Alarm.


Line Driver
A preamp level device that is intended to increase the level of preamp audio signal voltage between two devices, one of which is often an amplifier at the receiving end. The overall signal voltage increase is intended to maximize the signal input of the amplifier, thus keeping the input levels at the amplifier low and reducing the residual audible noise (hiss, etc.) that is present when amplifier levels are grossly mismatched with low input signal. While it can be a standalone device, it’s often a feature or value-added function of a device that has other signal processing features like preamp equalizers, digital processors, etc.


Line Output Converter (LOC)
A preamp level device that is intended to increase the level of preamp audio signal voltage between two devices, one of which is often an amplifier at the receiving end. The overall signal voltage increase is intended to maximize the signal input of the amplifier, thus keeping the input levels at the amplifier low and reducing the residual audible noise (hiss, etc.) that is present when amplifier levels are grossly mismatched with low input signal. While it can be a standalone device, it’s often a feature or value-added function of a device that has other signal processing features like preamp equalizers, digital processors, etc.


Loudness Control
Also called ‘Loud’ if labeled on a button. Loudness is feature on many aftermarket head units that boosts the low and high frequencies at low volume levels to better balance the human hearing frequency response at low volumes. Most loudness features automatically disengage at a certain upper volume range because the human ear hears those lower and higher frequencies much better at higher volumes.


Low Level Outputs
Another term commonly used to describe Preamp Level Outputs.


Low Pass
A filter type where only the frequencies below the filter point are allowed to pass. Low pass filters (also called low pass crossovers) can be active or passive. See also: Crossover.


MP3
MPEG 1, Audio Layer 3 is simply known as MP3. It’s a form of perceptual coding where some of the redundantly similar parts of a digital file can be discarded to reduce file size and not be noticed by the human ear upon playback. How much it’s noticed would depend on how much of the file is discarded to reduce file size. MP3 is a ‘lossy’ compression meaning that some of the file information is lost upon playback, but whether or not that’s audible to the human ear is part of its perceptual coding algorithm. The higher the bit rate (samples per second), the better the quality of playback. Higher bit rates also mean larger file size. 320kbit/second is the highest bit rate supported in the MP3 standard of encoding.


Nominal Impedance
An expression of an average impedance, commonly described in speakers and measured in units of ohms, that is close to the measured DC resistance of the speaker. Most speakers are rated at a nominal impedance value to better represents a flat line impedance response (rather than variable impedance on a curve) and by doing so is easier to match amplifier power ratings and amplifier operational loads. Example: “A speaker with a 4-ohm nominal impedance would connect to an amplifier that has a rated power delivered into a 4-ohm load.” See also: DC Resistance (DCR), Impedance.


Octave
A measure in music of increase or decrease across the audio spectrum that is exactly double (if moving up in frequency) or half (if moving down in frequency) of the starting frequency. Octave intervals are used to describe multiple things in car audio such as equalization intervals or crossover slope attenuation. The human hearing range of 20-20kHz covers about 10 octaves.


Ohm
An international electrical unit of measure for resistance. The most common use of the terminology is the nominal impedance of car audio speakers and subwoofers where the voice coil is rated in ohms.


OEM
Original Equipment Manufacturer. The terminology usually associated with factory installed parts or factory equipment. Example: “You can easily integrate with the OEM head unit and add aftermarket amplifiers as long as you have the appropriate integration device.” See also: Aftermarket.


Passive Crossover
A type of crossover that’s intended to be placed after the amplifier and before the speaker. Passive crossovers use only passive components like resistors, inductors and non-polar capacitors. Passive crossovers connected to the speaker wires, so no external power is required. Most high-end component 2-way speaker systems for the car include a 2-way passive crossover in one output (high pass) connects to the tweeter and one output (low pass) connects to the midrange/woofer. See also: Crossover and Active Crossover.


PBAP
Phone Book Access Profile. A subset of the Bluetooth Hands Free Profile (HFP) which specifies the functionality of the hands-free device to access (and often display) the contacts stored in the phone’s contact database. Depending on the level of PBAP functionality, users can view missed/received calls or even browse contacts and dial from their contact list on the hands-free device just as if they were using their phone. When the hands-free device supports voice command, it may also allow voice dialing or searches based on accessibility of the contacts through PBAP functionality.


Peak Power Handling
A designation given by the manufacturer for a speaker’s ability to handle power, typically a best case scenario for very short time period and not intended to represent continuous power handling. It’s often a threshold beyond which the speaker will knowingly fail (sort of like the redline on an engine’s RPMs). See also: RMS Power Handling.


Perceptual Coding
A digital music file compression scheme where some of the redundantly similar parts of a digital music file can be discarded to reduce file size and not be noticed by the human ear upon playback. How much it’s noticed would depend on how much of the file is discarded to reduce file size. Common perceptual coding styles include MP3, AAC, WMA and other file extensions.


Ported
Another name for a vented subwoofer enclosure that employs a design in which the subwoofer is installed into an enclosure with a vent (or port) that compliments the output of the subwoofer’s cone at the vent’s tuned frequency. The addition of the air column moving in the vent in harmony with the cone means an increase in output at that frequency. The drawback of the vented enclosure is that it’s important to ensure both the size of the enclosure and the vent length/diameter specifications are complimentary to the subwoofer. Without following some recommendation or planning, simply cutting a hole in a sealed enclosure will almost certainly provide a worse result so the dimensions of the vent are a very important part of how a vented enclosure performs. The other drawback is that, below the tuned vent frequency, the sealed enclosure has much lower power handling so it’s always recommended to use a subsonic (infrasonic) filter to limit those frequencies. There is not one identical size of enclosure for every woofer. See also: Vented, Sealed, Band-Pass Enclosure.


Preamp Outputs
These are outputs from a source unit, signal processor or other device that is in the signal path before the amplifier. They are generally analog signals, commonly 500mV to 8V, that connect with RCA audio cables. Analog preamp outputs and inputs can be recognized by their red (right channel) and white (left channel) RCA jacks on most car audio equipment. Since the signal level of all preamp outputs can be different, a ‘level matching’ control is a necessary part of a device receiving input. This level matching allows the two components to achieve optimum performance. On amplifiers this level matching control is commonly called the gain control, but it’s not intended (as some may mistakenly believe) to be a volume control. It’s intended to match the amplifier’s input stage to the signal level of the preamp outputs connected to the amplifier.


Presets
Most in-dash head units have user defined presets that allow instant recall of things like favorite AM/FM or satellite radio stations, or other sound control features that would normally involve multiple settings to achieve. Some high-end digital signal processors also feature presets that allow a user to have easy single button access to an optimized sound setting for that specific seating position, user listening preference (equalization) and even the source input. The intent of any presets is really to keep your attention focused on the road rather than fiddling with buttons on the equipment unnecessarily. Presets are about safety as much as about convenience.


Qtc
A description of the mechanical damping provided by a sealed subwoofer enclosure. The enclosure itself provides a degree of control (damping) for the subwoofer and by changing the physical size, the damping also changes. Very large sealed boxes have less damping than small sealed boxes. An over damped sealed enclosure (very small) is prone to poor low frequency response and a ringing effect. Audiophiles in the home audio world regard the Qtc value of 0.707 to be the best blend of deep bass, good transient response and output (SPL). In cars, it’s more frequent to see values of 0.9 or 1.0 to take advantage of slightly smaller enclosure volumes. The tradeoff of some low frequency losses can be made back up when the subwoofer box takes into account the acoustic effect of the car boosting some of that low frequency.


Radio Frequency (RF)
Radio waves between 3kHz and 300GHz that comprise the radio frequency spectrum. These waves travel through the air from a transmitter to a receiver and allow devices like AM/FM tuners and car security systems to receive signals freely as long as the receiver is within an acceptable range of the transmitter.


Rear Seat Entertainment (RSE)
The term used to describe video entertainment products and installations in which the intent of the devices are to provide entertainment to only rear seat passengers (not the driver or front seat passengers). This is often involving overhead ‘flip down’ or headrest mounted video screens and source units that can play media specifically for viewing on the screen(s) such as DVD players, game systems or portable devices with connectivity to the screens. RSE systems also often use wired or wireless headphones as a method for hearing the audio content rather than broadcasting that audio through the car’s speakers. See also: Zone 2.


Receiver
A device that receives a transmission of radio frequency (RF) waves, typically AM/FM or satellite radio when referred to in car audio terms. It could also be the RF receiver on a vehicle security, keyless entry or remote starter system that responds to keychain remote commands. When used to describe an in-dash head unit, a ‘receiver’ is one in which there is also built-in power to connect directly to speakers, whereas a ‘tuner’ only describes the AM/FM or satellite radio section of that head unit. See also: Tuner.


Remote Control
A wired or wireless method of controlling something separately from the main electronic component. Commonly, remote controls are used in car audio for head units (in-dash CD/DVD), rear seat entertainment screens and source units or security and convenience systems (such as car alarms and remote starters). Wireless remotes, depending on the application, can be line of sight (known as Infra Red) or available at a distance over radio waves (known as Radio Frequency). These days with some smart phone apps, wireless remote control can even occur over WiFi and cellular data channels.


 
Remote Starter
A device that allows the vehicle to start and remain running while unattended, thus not requiring the driver to open the door and turn the ignition key. Remote starters are popular in climates where warming up the car (or cooling it down) ahead of planned driving is advantageous to staying comfortable when entering the vehicle. Remote starters are able to be controlled from short range (50 feet) as in factory installed systems up to potentially thousands of feet with 2-way aftermarket systems. With a smart phone and compatible app, many remote starters can also be activated over a cellular data network or WiFi (if the optional service is activated) and controlled anywhere the phone has a signal. Generally speaking, remote starters are advised to be professionally installed because of their safety connections to vehicle circuits that ensure only safe and secure operation.


RMS Power Handling
A designation for a speaker’s ability to handle based on an amplifier’s rated RMS output power in watts. It’s based on an RMS output voltage measurement of an amplifier into the speaker’s nominal impedance as a load. Using Ohm’s Law it’s very easy to determine this RMS output power and this is where, if matched to the speaker’s RMS power handling, the speaker should play with no eminent risk of failure from overpowering. See also: Peak Power Handling.


Sealed
A type of subwoofer enclosure design in which the subwoofer is installed into a completely sealed, specifically sized enclosure that provides the air spring to move the subwoofer back from its electrical extension. The sealed volume is the restoring force and the actual size required depends on many of the subwoofer’s electro-mechanical parameters. There is not one identical size of enclosure for every woofer. See also: Acoustic Suspension, Vented, Band-Pass Enclosure.


Signal-to-Noise Ratio (S/N)
A measurement used in electronics to express how much signal is output relative to the ‘noise’ related to that piece of equipment. It’s expressed in units of decibels (dB) that represent a scale of what’s audible. The larger the number of signal versus noise, the better the specification. Amplifiers commonly have lower S/N specifications than a digital source (like a CD or DVD player), but even with 80-90dB of S/N it’s likely you’d be hearing more noises out on the road from tires, wind, etc. than the ‘noise’ of any electronics. In addition, a published S/N ratio presumes the equipment is electrically connected with adequate supply of current which makes the right wire size/type for amplifiers particularly important.


Single-DIN
The terminology that describes the internationally standardized size of an in-dash receiver in aftermarket car audio with dimensions of roughly 2” high x 7” wide. There is not a standardized depth for DIN receivers. The front panel of a DIN receiver is typically smaller than the dash panel opening and has a trim ring to cosmetically finish out any gaps.


Speaker Level Inputs
An audio input that is intended to be connected to signal wires normally connected to a speaker. This input is a common feature on many car audio amplifiers and integration devices that allow easy connection to a car’s existing audio system. Speaker level inputs are an alternative way to provide an audio signal to aftermarket devices when a preamp level audio signal is not available. Also sometimes called high level inputs.


Speaker Level Outputs
Any audio output that is intended to directly drive a speaker, usually referred to those outputs on a head unit. Since many head units contain both preamp level outputs and speaker level outputs, the terminology differentiates between the two types.


Subwoofer
A speaker intended to produce the lowest audible frequencies in the human hearing spectrum, typically 20-125Hz. The physical diameter of a speaker does not make it a subwoofer, rather it’s the ability to move air and reproduce those lowest frequencies effectively. The vast majority of subwoofers used in a car require the use of a matched enclosure to ensure the low frequency performance of the subwoofer in the space of the vehicle. Subwoofers have different power handling ratings, but nearly all subwoofers (regardless of brand, size or type) require the power of at least a modest amplifier to effectively produce low frequencies in the car. See also: Enclosure.


THD
An acronym for Total Harmonic Distortion. It’s a measurement of how much distortion the device adds to the signal. While most amplifier specifications are well below 0.1%, the most audible distortion actually comes from trying to overdrive an amplifier to make more power than it’s capable of reliably delivering. Most amplifiers rate the power output at 1% THD, which is about where the human ear can begin to distinguish the distortion when using audible test tones.


Time Correction
Also commonly called ‘Time Alignment.’ A term used to describe the delay of audio signals in specific channels of an audio system so that the arrival time of each channel at the listener’s ears are heard in a way where the listener perceives themselves to be sitting in the middle of the imaginary stage. This feature is used in car audio signal processors to address the fact that there is no middle seat in a car, only a right or left seat. Time correction is intended to reduce or eliminate the natural bias a listener would have sitting closer to one side of the car’s speakers than the other side.


Transceiver
A device that both receives and transmits signals. A transceiver in the car can be wireless (for RF signals) or wired (such as in vehicle computers sending and receiving commands). Wireless transceivers require some kind of antenna or unobstructed path to reception so that they can achieve a reasonable range between the wireless device and the vehicle where the transceiver is installed.


Transponder
A device using radio frequency identification (RFID) where devices can communicate with one another wirelessly, but in a predetermined proximity. Transponders are used in the automotive environment for encrypted security keys to allow the car to start and run only if the vehicle recognizes the specific transponder keys that have been learned to that vehicle. Many remote starters rely upon sophisticated transponder interface devices during remote starting to emulate the presence of the key in the vehicle, even when it’s not really there.


Tuner
A device that receives a transmission of radio frequency (RF) waves, typically AM/FM or satellite radio when referred to in car audio terms. All by themselves, tuners do not have power to drive speakers directly. See also: Receiver.


Tweeter
A speaker specifically designed to reproduce high frequency content, generally above 2kHz. Tweeters used in car audio systems are commonly of the domed design (a dome for a diaphragm rather than the concave cone of a woofer). The materials used in tweeter domes range from fabrics like treated silk to plastics to robust metals like aluminum or titanium. Tweeters are intended to be used with crossovers to limit the amount of low frequency that would otherwise add unnecessary heat and premature failure to the voice coil.


Valve Amplifier
Another name for tube amplifiers which, although not common in the car audio world, have a following among home audio enthusiasts for their ‘warm’ sound. The vast majority of car audio amplifiers use transistorized (or MOSFET) outputs because of their low cost and high reliability in the car.


Variable Bit Rate (VBR)
During digital file compression in formats like MP3, AAC, WMA, etc. some encoders offer variable bit rates to take the most advantage of recapturing the detail of a song in the complex parts (higher bit rate) whereas it will discard information in the less detailed parts (lower bit rate). This allows the playback to provide a good balance of sound quality and file size.


Vented
A type of subwoofer enclosure design in which the subwoofer is installed into an enclosure with a vent (or port) that compliments the output of the subwoofer’s cone at the vent’s tuned frequency. The addition of the air column moving in the vent in harmony with the cone means an increase in output at that frequency. The drawback of the vented enclosure is that it’s important to ensure both the size of the enclosure and the vent length/diameter specifications are complimentary to the subwoofer. Without following some recommendation or planning, simply cutting a hole in a sealed enclosure will almost certainly provide a worse result so the dimensions of the vent are a very important part of how a vented enclosure performs. The other drawback is that, below the tuned vent frequency, the sealed enclosure has much lower power handling so it’s always recommended to use a subsonic (infrasonic) filter to limit those frequencies. There is not one identical size of enclosure for every woofer. See also: Ported, Sealed, Band-Pass Enclosure.


Voice Coil
The coil of wire wrapped in insulated layers around a speaker’s centrally located former. The alternating current (in the form of an audio signal) traveling through the voice coil wire is how the diaphragm of the speaker moves in and out by attraction or repulsion from the speaker’s magnetic field.


Woofer
In a component speaker system, the larger diameter speaker is usually referred to as the woofer. This can be anywhere from 4” (100mm) on up to 18” (460mm) diameter speakers. One particular attribute is that a woofer, regardless of its physical size, may not be designed to play the very lowest bass notes. Those applications are handled by subwoofers which may cover some of the higher range that woofers cover too.


Watts
A measurement of electrical power output, handling or consumption. Most car audio equipment that connects directly to speakers is rated in output power capability of watts and generally stated into a specific ohm load (Example: 100 watts per channel into 4-ohms). Often the watts ratings are quantified as ‘max’, ‘peak’, ‘continuous’ or ‘RMS’, each of which is measured or qualified differently. RMS power ratings have the most accuracy and reliability for comparison purposes. Speakers themselves are also rated in watts, although it’s the amount of power they handle (power handling), not the amount of power they put out. Whenever comparing power ratings of amplifiers with power handling of speakers, always use the same qualifier – such as ‘RMS’ – to ensure that the comparison and matching is accurate.


X-over
A common abbreviation for a crossover, whether active or passive. Example: the amplifier includes an on-board active x-over.

Xmax
A term describing the maximum linear excursion distance that a speaker cone can travel within its operating limits. Sometimes the manufacturer specifies the measurement as ‘one-way’ (cone traveling only out or in) and other times it’s listed as ‘peak-to-peak’ (cone moving both all the way out and all the way back in, essential double the one way measurement). Since the way sound is reproduced in air involves the speaker’s cone moving the air, Xmax is an important performance attribute as frequency is decreased. As such, subwoofers are generally the car audio speakers with the highest Xmax specifications.


Y Adapter
An audio cable that has a single end that splits to two other (identical) ends. Y adapters used in car audio systems are commonly terminated with RCA ends and are used for taking one signal connection to two or the opposite, taking two signals and combining to one. Many RCA Y adapters are used when multiple amplifier channels are required and a two-channel stereo signal must be split to feed signal to those amplifiers.


Zone 2 (or Second Zone)
Many in-dash car audio head units with DVD or built in hard drive playback feature a second zone for sending audio/video signals to a different location in the vehicle. This is commonly used to deliver video to rear passenger screens and audio to headphones (either wired or wireless) so that a single head unit could display AM/FM or navigation for the driver and route the second source (such as DVD or hard drive movies) to passengers in the rear. The ‘zone’ terminology is commonly used in home entertainment systems so it’s a sensible adaptation to mobile audio/video systems with rear seat entertainment.

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