A

A-B Test: A test between two components. For example, a test between two different pre-amplifiers. For the test to be scientifically valid the levels should be matched.

ABX Comparator: A device that randomly selects between two components being tested. The listener doesn't know which device is being listened to.

AC3: See Dolby Digital

Acoustic suspension: A sealed or closed box speaker enclosure.

AES/EBU: Balanced digital connection. For example, used to connect a CD transport to a DAC. The AES/EBU standard uses XLR type connectors.

Alignment: A class of enclosure parameters that provides optimum performance for a woofer with a given value of Q.

Alpha: Term used in sealed enclosure designs to mean the ratio of Vas to Vb, where Vb is the volume of the box you will build.

Alternating Current (AC): An electrical current that periodically changes in magnitude and direction.

Ambience: The acoustic characteristics of a space with regard to reverberation. A room with a lot of reverb is said to be "live"; one without much reverb is "dead."

Ampere (A): The unit of measurement for electrical current in coulombs per second. There is one ampere in a circuit that has one ohm resistance when one volt is applied to the circuit. See Ohms Law.

Amplifier (Amp): A device, which increases signal level. Many types of amplifiers are used in audio systems. Amplifiers typically increase voltage, current or both.

Amplifier classes: Audio power amplifiers are classified primarily by the design of the output stage. Classification is based on the amount of time the output devices operate during each cycle of signal swing. Also defined in terms of output bias current, (the amount of current flowing in the output devices with no signal).

Analog: Before digital, the way all sound was reproduced.

Attenuate: To reduce in level.

Aperiodic: Refers to a type of bass-cabinet loading. An aperiodic enclosure type usually features a very restrictive, (damped), port. The purpose of this restrictive port is not to extend bass response, but lower the Q of the system and reduce the impedance peak at resonance. Most restrictive ports are heavily stuffed with fiberglass, dacron or foam.

Audiophile: A person obsessed with the reproduction of music at the highest level of fidelity. Prone to irrational equipment changes based on subjective reviews of equipment with no relevance to their musical tastes and desires.

AWS: Adaptive Woofer System, trademark of ACI. An active woofer system with built in user adjustable equalization capabilities.