Decibel (dB) The standard unit of measure for expressing relative power or amplitude differences. with audio, it represents loudness. One dB is the smallest change in loudness most people can detect. A 1 dB difference is barely noticeable, but a 10 dB difference is big — a speaker playing at 10 dB higher volume will sound roughly twice as loud. A 3dB difference equates to a doubling of power.
Diaphragm The part of a speaker driver that moves, producing the sound. Each diaphragm is directly connected to a voice coil. The diaphragm for a woofer is a cone, while for a tweeter, it's often a dome.
Diffusion The scattering of sound. Diffusion reduces the ability of a listener to pinpoint the actual location of a speaker, a useful quality in surround speakers. Diffuse surrounds create a wraparound soundfield that draws you into the on-screen action.
Dipole A speaker design that uses two sets of drivers to generate equal amounts of sound both forward and backward, or side to side, with the two sounds being "out of phase.” Dipoles are often used as surround speakers, and are very effective at creating a diffuse soundfield when placed on the sides of the listening position.
Direct and reflected sound The sound that you hear from your listening/viewing position is a combination of the direct sound that travels straight from your speakers to your ears, and the indirect, reflected sound — the sound from your speakers that bounces off the walls, floor, ceiling or furniture before it reaches your ears.
Dispersion The degree to which a speaker's sound is spread over the listening area.
Dolby Digital An encoding system that digitally compresses up to 5.1 discrete channels of audio (left front, center, right front, left surround, right surround, and LFE) into a single bitstream, which can be recorded onto a DVD, HDTV broadcast, or other form of digital media. A Dolby Digital processor (found in most receivers purchased after 2005) can decode this signal back into the 5.1 separate channels. Most films are recorded in a 5.1 digital format, though a number of films before 1992 had 6-channel analog tracks that have been remastered into 5.1.
Driver Any individual diaphragm (cone, dome, etc.) within a speaker that compresses and rarefies the air to create sound waves, such as a woofer, tweeter, midrange, etc.
DVD Officially known as the Digital Video Disc, though marketers unofficially refer to it as the Digital Versatile Disc. DVD uses a 5-inch disc with anywhere from 4.5 Gb (single layer, single-sided) to 17 Gb storage capacity (double-layer, double sided). It uses MPEG2 compression to encode 720:480p resolution, full-motion video and Dolby Digital to encode 5.1 channels of discrete audio. The disc can also contain PCM, DTS, and MPEG audio soundtracks and numerous other features. An audio-only version, DVD-A uses MLP to encode six channels of 24-bit/96-kHz audio.
Dynamic range The difference between loud and soft sounds. A speaker with wide dynamic range — one that can reproduce the sudden and wide changes between loud and soft sounds in music and video soundtracks — will sound more realistic (all other things being equal).
Efficiency The efficiency rating for a speaker is a measure of 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.
Equalizer A component designed to alter the frequency balance of an audio signal. Equalizers may be graphic, parametric, or a combination of both.
Home Audio Glossary of Terms has been created to inform and educate individuals interested in building a home theater environment. These home audio terms relate to all words beginning with the letters D and E, such as decibal or db, diaphram, diffusion, dipole, direct and reflected sound, dispersion, dolby digital, driver, DVD, efficiency, and equalizer.