Capacitance - The ability of a conductor or dielectric to store electric charge. Capacitance is measured in Farads, and micro or pico-farads for smaller units.

Capacitor (Cap) - There are two types of capacitors. A Polarized Cap is an electrical device consisting of two metallic plates separated by a dielectric. These are commonly used in mobile audio systems, also referred to as Power Caps or Stiffening Caps. These Capacitors store excess energy during intervals when it is not required and release it when demand exceeds what is available from the car's power system. The second type, a Non-Polarized Capacitor, is used as crossover components to filter out lower frequencies and allow higher frequencies to pass.

CD Text - Data that can be encoded on a compact disc that contains disc, track, and artist information. Playback device must have CD Text compatibility to utilize this feature.

CD Receiver - Also referred to as CD Head Unit. An indash radio receiver that also incorporates a CD Player in it.

Chassis - This term could refer to either the metal frame of a vehicle or to the frame of an audio component. A Chassis is generally where the main source ground is found.

Center Channel - Refers to a speaker located between the left and right front speakers. This speaker reproduces a signal encoded to enhance voices and sounds associated with the center of the front sound stage. Center channel signals are found in 5.1, 6.1, DTS and Super Audio recorded material.

Channel - In the case of an amplifier, it refers to one complete amplifying section of the amp that produces an independent audio signal. Most amplifiers are configured as 1, 2, 4, 5, or 6 channel units. Channel may also be used in reference to audio signals as they occur in a 3D environment. For example - left, right, center or rear audio channels.

Channel Separation - The ability to keep one channel of a stereo signal apart from the other. Output devices with poor Channel Separation would allow some of left or right channel to bleed over the other channel, causing it to produce less of a stereo effect and sound more monophonic. Expressed in decibels (dB). The higher the dB rating, the better the stereo effect produced.

Circuit - Any closed path through which an electrical current flows. Circuit may also refer to a configuration of electrically or electromagnetically connected components or devices.

Circuit Breaker - A device that protects electric circuits by opening the circuit, thus interrupting power, when an overload occurs. Once tripped it can be manually reset, unlike a fuse. The threshold at which they trigger is rated in amperes (amps).

Clipping - A signal that results from an amplifier that is either overloaded or underpowered relative to the size of signal it being asked to produce. A normal AC audio wave consists of gently rounded peaks and valleys. A clipped waveform yields what looks a lot like a square or alternating DC wave.

When DC is applied to a speaker, the voice coil has no means of propelling itself throughout the flat part of the wave. Instead, it can only convert the incoming current to heat, and ultimately burns up. The effect of alternating DC on speakers is remarkable, irritating, painful, and short. If you are able to hear evident Distortion at high volume levels or smell smoke, reduce the volume. Clipping is the main cause of blown speakers.

CMS (a Theile Small parameter ) - Refers to the compliance (the opposite of stiffness) of the mechanical suspension of a speaker cone, consisting of the spider and surround.

Coaxial - A speaker consisting of larger cone for lower range frequencies and a smaller cone or tweeter for higher frequencies aligned on the same axis. These two speakers work in conjunction with using a built-in passive crossover network or if the speakers are to be bi-amplified, the built-in crossover is bypassed and an active crossover will be used to allow the two amplifier channels to produce the proper range of frequencies for each of the two speakers.

Coil - Also called an Inductor or Choke. A crossover component used to filter out higher frequencies and allow lower frequencies to pass.

Coulomb - The amount of electric charge carried by a current of 1 ampere.

Common Ground - Grounding points that are sharde. Found in lower powered amps and head units where the left and right channel outputs share a ground path.

Compliance - The measurement in liters or cubic feet of the volume of air that is equal to the maximum extension of a speaker's total suspension. Determines how easily a speaker cone/ voice coil assembly will move when an electrical signal is applied to it.

Compression (Audio) - The process of reducing the dynamic range of a given analog audio program by making the loud parts quieter and the quiet parts louder.

Compression (Audio/Video Files) - A process of reducing audio or video data for more efficient storage or transmission. A temporary reduction in file size is called 'non-lossy' compression, and no information is lost. A permanent reduction in file size (such as with mp3 or mpeg files) is called 'lossy' compression. This process discards low priority or (supposedly) unnecessary information which is permanently lost. This type of process usually lets you choose the level of file compression. The more the original signal is compressed, the poorer the playback quality is although it allows more files to fit into a storage device (ie: a USB thumb drive).

Compression Driver - Compression drivers usually consist of a magnet and coil arrangement with a small diaphragm as the main transducer. These drivers are usually coupled to the throat of an exponential horn. Such an arrangement enables this type of tweeter to have very high directional characteristics and increased output. In typical car stereo near-field applications, specialized horns are required to prevent these from being too narrowly directional.

Concert Pitch - The standard frequency (internationally agreed on in 1960) for the tuning of musical instruments. This pitch is the note A above middle C and has a frequency of 440 Hz.

Conductor - Materials along which electrons will flow, making them suitable for use as a connecting link in electrical circuits.

Cone - Refers to the diaphragm used for the radiating surface of a loudspeaker. This is directly attached to the voice coil motor allowing it to produce pulsating columns of air (Waves) that the ear detects as sound (click here for Speaker parts diagram). Also useful for holding ice cream.

Constant 12V (+) - A lead, wire, or connection point that shows positive 12 volts regardless of ignition key position.

Continuity - The ability to pass a signal or current from one end of a path (lead, wire or circuit) to the other.

Crossover - An active device or passive circuit used to take a full range input signal and output various frequency signal bands. It Rolls Off frequencies above and/or below certain points in the range, allowing the signal to be tailored for the specific driver to which it is sent. For diagrams of different passive crossover designs, see Passive Crossover Networks.

Crossover Frequencies - The frequencies at which an active or passive crossover network divides audio signals, which are then routed to the appropriate amplifiers or speakers. Expressed in Hertz (Hz).

Crossover Point - Same as crossover frequency.

Crossover Slope - The rate at which a crossover circuit attenuates (or turns off) the blocked frequencies. Slope is expressed as decibels per octave. A 6dB per octave crossover reduces signal amplitude level by 6dB in every octave starting at the crossover point. Every time the frequency of the audio signal is changed by a factor of 2 (one octave), the level of the audio signal drops 6dB. For example, if a low-pass crossover is set at 80Hz with a 6dB slope, you'll see a drop in level of 6dB at 160Hz. If that crossover had a 12dB slope, you would see that 6dB drop at 120Hz. With slopes of 12dB and higher, the frequencies beyond the crossover points would be inaudible.

Crosstalk - The amount of undesirable interference on one stereo channel caused by the leaking of the other stereo channel. The higher the rating in decibels (dB), the better the Channel Separation.

Current - The rate of flow of electricity, expressed in amperes (amps). This measures the volume of the flow of electrons through a conductor, as opposed to voltage, which is the measure of the intensity or velocity of the electrical flow.

Cutoff Frequency - The frequency at which a signal falls off by 3 dB (the half power point) from it's maximum value. Also referred to as the -3 dB points or the corner frequencies.

Cycles Per Second - Refers to the amount of times a signal completes one full wavelength. Also referred to as Hertz (Hz)