C-D

C

Cabin gain
The low frequency boost normally obtained inside a vehicle interior when subs are properly mounted.

Capacitor
A device made up of two metallic plates separated by a dielectric (insulating material). Used to store electrical energy in the electrostatic field between the plates. It produces an impedance to an AC current (Alternating Current).

CENTRE Channel (or center (US))
In home theater, sound decoded from the stereo signal sent to a speaker mounted in front of the listener, specially designed to enhance voices and sound effects from a movie soundtrack. Used in car audio to help offset skewed stereo imaging due to seating positions in the automotive environment.

Channel Balance
In a stereo system, the level balance between left and right channels. Properly balanced, the image should be centered between the left-right speakers. In a home-theater system, refers to achieving correct balance between all the channels of the system.

Chorus (Refrain)
A musical phrase normally based on a single-note melody line. A key component of an arrangement, it is a song's central motif that ups its recognition factor.

Clipping
Refers to a type of distortion that occurs when an amplifier is driven into an overload condition. Usually the "clipped" waveform contains an excess of high-frequency energy. The sound becomes hard and edgy. Hard clipping is the most frequent cause of "burned out" tweeters. Even a low-powered amplifier or receiver driven into clipping can damage tweeters which would otherwise last virtually forever.

Class A, Class A-B etc...
In a sense, amplifying the audio signal means using the wall-current (usually either 120 or 240 volts) to increase the amplitude of the audio signal from mill-watts to watts. Different classes of amplifiers accomplish this in different ways. Turning a vacuum tube "on" or "off" with current demand increases the efficiency of the amplifier but may add switching distortion. A Class A amplifier is relatively inefficient, converting much energy to heat, but has no switching distortion.

Cms
Mechanical suspension compliance of a driver, consisting of the spider and surround.

Co-axial
A speaker type that utilizes a tweeter mounted at the center of a woofer cone. The idea being to have the sound source through the full frequency range become "coincident".

Coaxial Driver
- a speaker composed of two individual voice coils and cones; used for reproduction of sounds in two segments of the sound spectrum. See also triaxial driver.

Coherence
Listening term. Refers to how well integrated the sound of the system is.

Coloration
Listening term. A visual analog. A "colored" sound characteristic adds something not in the original sound. The coloration may be euphonically pleasant, but it is not as accurate as the original signal.

Compliance
The relative stiffness of a speaker suspension, specified as Vas.

Compression
In audio, compression means to reduce the dynamic range of a signal. Compression may be intentional or one of the effects of a system that is driven to overload.

Crossover
A frequency divider. Crossovers are used in speakers to route the various frequency ranges to the appropriate drivers. Additionally, many crossovers contain various filters to stabilize the impedance load of the speaker and or shape the frequency response. Some crossovers contain levels controls to attenuate various parts of the signal.
A passive crossover uses capacitors, coils and resistors, usually at speaker level. A passive crossover is load dependent (the transition may not be very smooth or accurate if a different speaker is substituted for the one the crossover was designed for).
An active crossover is based on integrated circuits (ICs), discreet transistors or tubes. An active crossover is impedance buffered and gives a consistent and accurate transition regardless of load.

Crossover Slope
High and low pass filters used for speakers do not cut-off frequencies like brick walls. The rolloff occurs over a number of octaves. Common filter slopes for speakers are 1st through 4th order corresponding to 6db/oct to 24db/oct. For example, a 1st. order, 6db/oct high pass filter at 100hz will pass 6db less energy at 50Hz and 12db less energy at 25Hz. Within the common 1st through 4th filters there is an endless variety of types including Butterworth, Linkwitz-Riley, Bessel, Chebychev, etc. Salesmen and product literature will sometimes make claims of clear superiority for the filter used in the product they are trying to sell. Since the subject fills books, suffice it to say that there is no one best filter, it depends on application and intended outcome. Good designers use the filters required to get the optimum performance from the system.

Cross-talk
Unwanted breakthrough of one channel into another. Also refers to the distortion that occurs when some signal from a music source that you are not listening to leaks into the circuit of the source that you are listening to.

Cutting
The process of removing unnecessary or undesirable sections of an audio or MIDI recording.


D

DAC
A Digital to Audio Converter. Converts a digital bitstream to an analog signal. Can be a separate "box" that connects between a CD Transport or CD Player and a pre-amplifier.

Damping (Damping factor)
Refers to the ability of an audio component to "stop" after the signal ends. For example, if a drum is struck with a mallet, the sound will reach a peak level and then decay in a certain amount of time to no sound. An audio component that allows the decay to drag on too long has poor damping, and less definition than it should. An audio component that is overdamped does not allow the initial energy to reach the full peak and cuts the decay short. "Boomy" or "muddy" sound is often the result of underdamped systems. "Dry" or "lifeless" sound may be the result of an overdamped system.

D'Appolito
Joe D'Appolito is credited with popularizing the MTM (Midrange-Tweeter-Midrange) type of speaker.

Decibel (dB)
Named after Alexander Graham Bell. We perceive differences in volume level in a logarithmic manner. Our ears become less sensitive to sound as its intensity increases. Decibels are a logarithmic scale of relative loudness. A difference of approx. 1 dB is the minimum perceptible change in volume, 3 dB is a moderate change in volume, and about 10 dB is an apparent doubling of volume:
· 0 dB is the threshold of hearing, 130 dB is the threshold of pain.
· Whisper: 15-25 dB
· Quiet background: about 35 dB
· Normal home or office background: 40-60 dB
· Normal speaking voice: 65-70 dB
· Orchestral climax: 105 dB
· Live Rock music: 120 dB+
· Jet aircraft: 140-180 dB

Defragmentation
A process by which data on a hard disk is rearranged in an order that enhances performance. Special defragmenting utilities are available for Windows and Mac OS.

Diaphragm
The part of a dynamic loudspeaker attached to the voice coil that moves and produces the sound. It usually has the shape of a cone or dome.

Diffraction
A change in the direction of a wave front that is caused by the wave moving past an obstacle.

Dipole
An open-back speaker that radiates sound equally front and rear. The front and rear waves are out of phase and cancellation will occur when the wavelengths are long enough to "wrap around". The answer is a large, wide baffle or to enclose the driver creating a monopole.

Direct Current (DC)
Current that moves in only one direction.

Dispersion
The spreading of sound waves as they leave a source. The spreading of sound waves as they leave a source.

Distortion
Anything that alters the musical signal. There are many forms of distortion, some of which are more audible than others. Distortion specs are often given for electronic equipment which are quite meaningless. As in all specifications, unless you have a thorough understanding of the whole situation, you will not be able to make conclusions about the sonic consequences.

DIY
Abbreviation for Do- It-Yourself. In audio, the most common DIY is building speakers but some hobbyists build everything from pre-amps to amplifiers to DACs.

Dolby Digital
Five-channel system consisting of left, center, right and left rear, right rear channels. All processing is done in the digital domain.
Unlike Dolby Prologic in which the rear effects channels are frequency limited to approx. 100-7000Hz, Dolby Digital rear channels are specified to contain the full 20-20Khz frequency content.
The AC3 standard also has a separate subwoofer channel for the lowest frequencies.

Dolby Digital EX Surround
Also referred to as Dolby Digital 6.1, adds a rear, center channel to the existing left, center, right and rear speakers. This format requires a 6.1 processor or receiver and DVDs that are 6.1 encoded.

Dolby Prologic
Four-channel system consisting of left, center, right and rear channel, (the single rear channel is usually played through two speakers).

Dome Tweeter
A high frequency speaker with a dome-shaped diaphragm.A high frequency speaker with a dome-shaped diaphragm.

Double (Dual) Voice Coil (DVC)
A voice coil with two windings, generally used in woofers. Each voice coil can be connected to a stereo channel, or both voice coils can be wired in parallel or series to a single channel.

DTS
Digital Theater System. A multi-channel encoding/decoding system. Used in some movie theaters. Also now included in some home-theater processors. A competitor to Dolby Digital.

DSP
Digital Signal Processing. DSP can be used to create equalization, compression, etc. of a digital signal.

DVD
Digital Video Disc or Digital Versatile Disc. A relatively new standard that seeks to combine better-than-laser-disc quality video with better-than-CD quality audio in a disc the size of a CD. Requires special players. Seems to be a viable candidate to replace both Laser Discs and CDs, but the jury is still out.

Dynamic Headroom
The ability of an audio device to respond to musical peaks. For example, an amplifier may only be capable of a sustained 100 watts, but may be able to achieve peaks of 200 watts for the fraction of a second required for an intense, quick sound. In this example the dynamic headroom would equal 3 db.

Dynamic range
The range between the loudest and the softest sounds that are in a piece of music, or that can be reproduced by a piece of audio equipment without distortion (a ratio expressed in decibels). In speech, the range rarely exceeds 40 dB; in music, it is greatest in orchestral works, where the range may be as much as 75 dB.