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Acoustic Lens: In loudspeakers, a mechanical device used to improve the dispersion of high frequencies, so that dispersion is much more uniform across the audible spectrum. The lens is a product of post-World War II Bell Labs research, first described in 1949. The intent is to focus sound in much the same way that an optical lens focuses light. An axiom called Snell's law describes the refraction of sound as it passes through an interface between two materials of differing sound speed. A high-frequency loudspeaker mechanical acoustic lens spreads a single-point sound source into a parallel wave front. Originally introduced commercially by JBL in the 1950s, they appeared in two primary designs. First was the slant-plate lens, which utilizes a series of plates with carefully calculated hyperbolic shapes, which results in a horizontal response pattern. This is the most commonly seen acoustic lens type. Second is the perforated-plate lens assembly, which consists of a collection of perforated barriers at the horn mouth. These perforated screens are actually ring shaped with varying sizes of center cutouts. Although acoustic lenses gradually fell out of favor through the 1970s and 1980s (partially due to their fragility, which made them risky to use in portable sound reinforcement systems), the technology has re-emerged in some high-end home audio systems (notably Bang & Olufsen) in recent years.

A & R	A-B Stereo	A-Time
A-weighted	A440	AAC - Advanced Audio Coding (also MPEG-2 AAC)
AAF	Abalone	ABS
Absolute Phase	Absorption	Absorption Coefficient
Alternating Current (AC)	AC-1	AC-2
AC-3	Academy Curve	A cappella
Accent	Access Time	Accidental
Accompaniment	Accumulator	Acetate
Acoustic Lens	Acoustic Suspension	Acoustic Treatment
ACPI	Action	Actionflo
Active	Active Sensing	Actuator
Adagio	ADAT	ADAT/FST
ADAT Optical	ADB	A/D Converter (ADC)
Additive Synthesis	Adjusto-Matic	ADPCM
ADR	ADSR	Aeolian Harp
Aerophone	AES	AES/EBU
AES3	AES3id	AES42-2001
AFL	AFM	Aftertouch
AFTRA	AGC	Aggregate Device
Aging Toner	Agitato	AGP
AHDSFR	AIFF (Audio Interchange File Format)	AIR
AIT	Alder	Alder
Aleatoric Music (Composition)	Algorithm	Alias
Aliasing	Alkaline Battery	All-Button Mode
All-Notes-Off	Allegro	Alnico
Alteration	Altered Chord	Alternate Tuning
Alto	AM	Ambience
Ambisonics	Amen Break	Amperage
Ampere	Amp Head	Amplifier
Amplifier, Instrument	Amplitude	AMS
Analog	Analog Sequencer	Analog Synthesizer
Anamorphic	Andante	Anechoic
Anode	Anodize	Anodized
ANSI	ANSI A-Weighting	Antecedent and Consequence
Antenna	Antenna gain	Anti-Imaging Filter
Anti-Aliasing Filter	Anti-node	Aperiodic
API	Apoyando	Apple Talk
Application (Program)	Architecture	Archival Stability
Archtop Guitar	Arco	ARP Avatar
Arpeggiator	Arpeggio	Arrangement
Articulation	Artificial (or Automated) Double Tracking or ADT)	ASCAP
ASCII	Ash	Ashtray Bridge Cover
ASIC (Application Specific Integrated Circuit)	ASIO	Aspect Ratio
Asperity	ASPI	Asynchronous
ATA	ATA-2	ATA 66/100/120
ATAPI	Absolute Time Code	Atonal Music
ATRAC	ATRAC	Attack
Attenuation	Audio	Audiobook
Audiology	Audio RIP	Audio Suite
AudioUnits	Audiowire	Auditory Cortex
Augmented Interval	Auranomic	Author
Authorize	Auto Accompaniment	Autolocate/Autolocator
Automata	Automatic Mixer	Automation
Auto Punch	Aux Send	AVI
AWG (American Wire Gauge)	AWM	Axe