DAC – Digital to Analogue converter, turning on/off pulses into analogue sound. CD players have DACs built in. Separate DACs can upgrade a CD player or other digital player/ recorder, or can be used with dedicated CD transports.
Damping - the reduction of movement of a speaker cone, due either to the electromechanical characteristics of the speaker driver and suspension, the effects of frictional losses inside a speaker enclosure, and/or by electrical means.
Damping Factor - This is a quantity which defines how quickly the amplifier can stop a reproduced frequency such as a bass note. The higher the damping factor, the better the amp will control the woofer and help reduce overhang distortion. The damping factor of an amplifier is mostly dependent on the quality of the power supply which feeds the power amp.
Damping Material - any material added to the interior of a speaker enclosure to absorb sound and reduce out-of-phase reflection to the driver diaphragm (cone). Usually acoustic fiberglass, polyester batting, or Polyfill is used in speaker enclosures.
Decibel (dB) - (1) a logarithmic scale used to denote a change in the relative strength of an electric signal or acoustic wave. It is a standard unit for expressing the ratio between power and power level. Using the logarithmic relationship for power PdB = 10*log[Pout/Pin] , a doubling of electrical power only yields an increase of +3 dB. Increasing the power tenfold will yield an increase of +10 dB and is a doubling of perceived loudness. The decibel is not an absolute measurement, but indicates the relationship or ratio between two signal levels. (2) SPL (sound pressure level) can be measured in dB. 0 dB represents the threshold of normal human hearing, 130 dB represents the threshold for pain, 140 dB causes irreparable hearing damage, and 150 dB can cause instant deafness, anything greater than about 192 dB can kill you.
De-interlaced video - Most video sources, including DVD, standard-definition TV, and 1080i high-definition TV, transmit interlaced images. Instead of transmitting each video frame in its entirety (what is called progressive scan), most video sources transmit only half of the image in each frame at any given time. Deinterlacing is the process of stitching back together, properly, the individual fields into a solid frame of video.
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.
Diffusion - The scattering of sound.
Dipole - A speaker design which generates equal amounts of sound both forward and backward, with the two sounds being out of phase. Dipoles are often used as surround speakers.
Direct Current (DC) - current in only one direction.
Diffraction - a change in the direction of a wave that is caused by the wave moving past or hitting an obstacle.
Dispersion - the spreading of sound waves as it leaves a speaker.
Distortion - any undesirable change or error in the reproduction of sound that alters the original signal.
Dome Tweeter - a high frequency speaker driver with a dome-shaped diaphragm usually made of metal or silk.
Driver - a loudspeaker unit, consisting of the electromagnetic components of a speaker, typically a magnet and voice coil.
DRM - a term referring to technologies used to control usage of digital media - including hardware controls to deactivate unauthorized use.
Dynamic range - the range of sound intensity a system can reproduce without compressing or distorting the signal.