DAC (D/A) - Digital to analog converter. A component or circuit that is used to derive or convert an analog signal from a digital one.

D'Appolito Arrangement - A mid-tweeter-mid speaker layout created by Joe D'Appolito that delivers enhanced imaging.

Damper - The part of the suspension connected to the bottom of the speaker cone at the voice coil that centers the voice coil in the magnetic gap. It is also referred to as the spider.

Damping - The reduction of resonance. Is also used to refer to the ability to keep a speaker cone that was producing output from continuing to resonate in the absence of an input signal, thus reducing distortion and improving bass accuracy.

Damping Factor - The ability of the amp to control the speaker. Simply put, a speaker is a coil of wire moving back and forth in a magnetic field. As the coil moves around, it's actually generating electricity. The more it moves, the more it creates. This interferes with the signal the speaker receives from the amp. The better the amp can overcome this interference, the better it can control the speaker - that's Damping Factor.

DC (Direct Current) - An electrical current that flows in one direction.

DC/AC Converter - A device that converts 12V DC power, like that from a car battery, into AC current so that AC devices can be used.

DC/DC Converter - A group of components within an amplifier that converts battery voltage (DC) into AC so that it can be increased by the switching devices and transformers and then converted back to DC (rectified) to provide higher voltage to drive the amplification stage.

Decibel (dB) - One tenth of a Bel. A unit of measurement for the ratio of loudness. The threshold of hearing is 0 dB. One dB SPL is the smallest audible difference in sound level. When you double amplifier wattage or cone area on a speaker system, you will generally get a difference of 3 dB.

Delay - Can also be referred to as Time Alignment. A signal processing device or circuit used to delay one or more of the output signals by a controllable amount. This allows the sound from speakers at varied distances away from the listener to be timed to arrive at the same time.

Detent Controls - A control device that uses a knob that has precise click-stops at regular points to indicate how much the control has been turned up or down.

Diaphragm - The sound-producing element in a tweeter, or Horn . This is the surface that produces the sound you actually hear. The motor assembly that drives it can be Piezo (no voice coil), conventional dynamic (uses voice coil) or a ribbon type. Diaphragms do not produce low and low midrange frequencies well, so they are not usually found in that application.

Die-Cast Basket - A type of speaker basket or frame that is cast as a single piece of relatively thick, rigid metal. This contrasts with a Stamped frame that is shaped by pressure, much like a car body fender. Cast metal is more dense and rigid, thus less likely to "ring" at certain frequencies (click here for Speaker parts diagram).

Dielectric - An insulating material with low electrical conductivity.

Diffraction - a change in the direction and velocity of a sound wave that is caused by the wave moving past an obstacle.

DIN - Acronym for Deutsche Industrie Normung, the German standardization body. A world reference standard for the mounting parameters of many common indash receivers and components. Single DIN is the standard face size for most receivers, and measures 7-3/8"wide by 2-1/4" high. DIN+1/2 measures 7-3/8"wide by 3-3/8"high. Double DIN measures 7-3/8"wide by 4-1/2" high.

Diode - An electrical circuit element that allows current to flow in one direction.

Directional - The angle at which a speaker disperses sound. Higher frequencies are narrower than lower frequencies. Tweeters are more directional than woofers. If a speaker is very directional, it's easy to be able to audibly locate it.

Discharge - In a capacitor, the release of stored energy to a load.

Dispersion - The radiated acoustical pattern of sound a speaker emits over a given area.

Distortion - Any departure from a true and accurate reproduction of the original waveform. It can include Noise, Clipping Distortion, Harmonic, and Intermodulation Distortion . The last two types are fairly common in speakers and can be reduced but not entirely eliminated with today's technology. Most modern amplifier designs eliminate nearly all forms of inherent perceived distortion, leaving only that caused by inappropriate user settings and overloading.

Diversity Tuner - An FM tuning method which employs a dual antenna system. In most applications, one antenna is mounted in the front and one in the rear of the vehicle. Since FM broadcasts are are a line-of-sight type of transmission, the tuner can switch between the two antennas and uses the one getting the best reception.

Dolby - A patented noise reduction system that increases dynamic range and signal-to-noise ratio of Dolby encoded tape media.

Dolby Digital - Dolby's name for its format for the digital multi channel soundtrack system, first used in motion picture playback. Also called Dolby Pro Logic. Utilizes their AC-3 method of digital compression. Dolby Digital decoder systems automatically contain Dolby Pro Logic processing to ensure full compatibility with the many existing program soundtracks made with Dolby Surround encoding. This system, referred to as 5.1, utilizes six channels of information. These channels go to front left, front right, center (front), surround right (rear) and surround left (rear) speaker systems plus a subwoofer.

Two other variations include Dolby Digital EX (6.1) and Dolby Pro Logic IIx (7.1), which which move the surround speakers to the sides and incorporates one or two more additional back speaker systems placed behind the listener.

Dome - A convex speaker or diaphragm shape usually used for tweeters. They are efficient, and have low distortion and wide dispersion. They can be made out of either hard or soft materials.

Dot Matrix Display - A type of display that employs regularly spaced patterned grids of lighting elements, giving it greater resolution than a segmented display.

Double Stacked Magnets - Two magnets overlaying each other to increase the overall magnetic field (click here for Speaker parts diagram).

DPDT (Double Pole Double Throw) - A term used to describe a relay or switch that has two separate contacts (poles) and can throw (make electrical contact) to either pole to complete a path with the source signal. May also be called an A/B switch.

Driver - An alternate term for speaker, transducer, or radiator. Also refers to a device attached to a horn for acoustic coupling and controlled dispersion of sound.

Driver Volume - The amount of enclosure airspace that is displaced by the speaker itself.

DSP (Digital Signal Processing) - A type of processing accomplished by digital hardware specifically designed for digital signal manipulation. Also refers to a component using such processing.

Dual Mode - An amplifier configuration in which both a stereo speaker pair and mono speaker system (usually a subwoofer) are simultaneously powered by a stereo amplifier. Passive crossovers are needed to insure speakers produce appropriate range of frequencies (except for mono center channel applications).

Dust Cap - A rigid cardboard or plastic dome placed over the open top of the voice coil to keep foreign material from falling into the voice coil and causing damage to it (click here for Speaker parts diagram).

Dynamics - When used in music, refers to the varying degree of loudness and softness in a musical performance.

Dynamic Noise Reduction (DNR) - A signal-processing circuit that reduces the level of high frequencies. Unlike Dolby Noise Reduction, DNR works with any media does not require specially encoded material.

Dynamic Range - The difference between the softest and loudest portions of sound or music passage being reproduced. Expressed in decibels, the higher the number the better.

Dynamic Range Suppression - A signal compression technique which reduces the dynamic range without affecting overall volume of the sound being reproduced. When used with extremely dynamic music passages, can help prevent clipping in an amp or overextension of the speakers.