Acoustic feedback to Adiabatic

Acoustic feedback to Active current

system a Sabin is equivalent to a 1 square metre opening.

Typical Acoustic Absorption
. Coefficients
Material Coefficient
Open window 1.00
Special acoustic materials 0.30 to 0.9
Hair felt 0.58
Carpets 0.15 to 0.2
Smooth wood 0.04
Plaster 0.003
Glass 0.027
Brick 0.025
Acoustic feedback. Unwalted acous­ tic interaction between output and input of an audio system, usually between speaker system and mi­crophone or turntable cartridge, can lead to "howl".
Acoustic isolation. Methods and practices that will prevent sound in one area from leaking into an­other area; soundproof walls be­tween a studio and control room will have accous-tic isolation to prevent sounds in the studio from being heard (leaking) in the con­trol room, or vice-versa; acoustic "flats" or baffles are another means
to provide acoustic isolation, and'
are often placed bet-wecn musi­cians in a studio to reduce the sound level of other musical in­struments being picked up by any given instrument's microphone.
Acoustic lens. Arrangement of plates or other wise control a sound wave-front.
Acoustic ...esistance unit. Device comprising absorbent material clamped in an open frame work for
fitting over normal port or over an . additional vent on reflex LS en­closures; helps to control reso­

nance of the speaker/enclosure system.
Acoustics. (Phys.) The science of sound; the' study of the effects of sound upon the ear. The acoustics of a room are said to be "good" or "bad" according to the ease or clearness with which sounds are perceived by the hearers.
Acre. A measure of land equal to 160.sq. rods, 4840 sq. yd., 43,560 sq. ft.
Acroteria. (Arch.) Small pedestals placed at the apex and at the ex­tremities of a pediment, usually without bases or plinths.
Acrylic resins. (Chern. Plast.) Methyl Methacrylate resin. The familiar Plexiglas and Lucite (British Perspex). These resins are clearer than glass, and are used in aeronautical domes, in light diffusers, special windows, outside displays, etc. One of their uses is in instrument lenses, and in contact lenses, and the resin will pipe light around corners.
Actinic rays. The light rays which
act on photographic emulsions.
Activate. To render more reactive:
excite.
Activator. Any impurity in a min­erai that causes luminescence.
Active component. The accepted term for denoting the component of the vector representing an al­ternating quantity which is in phase with some reference vector.
Active conductor. (Elec.) One' through which an electric current
is passing. .
.Active current. (Elec.) In alternat­ing current that part in phase with the voltage, or the effective en­ergy.as differentiated from 'the

Active device to Adillbatic

wanless or useless energy.
Active device. A component capable of controlling voltages or currents to produce gain or switching ac­tion in circuit; electron tubes, tran­sistors ICs etc.
Active material. (£lee.) In a storage battery it is referred to as the paste of the positive (grid) plate of the cell.
Active pressure. (Elec.) In alternat­ing current the effective voltage which produces a current, as dis­tinguished from impressed voltage of the circuit.
Actuate. To move, cause to move, or bring into action. Automobile en­gine valves are actuated by motion of the camshaft.
Acute angle. (Math.) One which is less than 90 deg., or less than a right angle.
ad. (Prillt.) A common abbreviation
for advertisement.
Adam. (Fum.) An English furniture style introduced by Adam brothers (1128-1792), usually decorated with Roman classic ornaments.
Adaptability. (phys.) Suitability; the degree of ease of adjustment to ex­isting conditions.
Adapter. A device by means of which objects of different size are made interchangeable.
Adapter plate. (Plast.) In injection molding, the plate-holding mold which fits press or platen.
ADC. Analog-to-Digial Converter. An electronic device used at the input of digital audio equipment to cOllvert analog electrical ~;ignals to digital values whose numbers represent the level and frequency information con-tained in the original analog signal.

Addendum. (Gear.) The point or por­tion of the tooth of a gear wheel lying outside the pitch circle.
Addendum circle. (Gem:) The outer circumference of a gear wheel.
Addition polymerization. (Plast.) A chemical reaction in which mole­culc;s combine through interaction of unsaturated groups without the splitting off of any by-products.
Additive synthesis. A technique for creating musical notes whereby sine waves are added together to create new waveforms. Usually used in electric organs rather than in synthesizers.
Adherence. The quality of clinging or sticking together of unlike par­ticles.
Adhesion or adhesive power. (Meclz.) The friction existing bet­ween a driving wheel and the sur­face with which it is in contact. (Mech. Arts) The property which
enables one surface to adhere or stick to another, as in glue prac­tice. (Plast.) In plastics, a state in which two faces 'are held together by a plastic adhesive, or by the plastic itself, after its faces have been softened by a solvent.
Adhesion-Cohesion (MagneticTape). Characteristics:
1. Adhesion. The degree to which a coating adheres to the base film.
2. Cohesion. The degree to which acoating is bOlllld to itself.
3. Anchorage. A general term de­scribing both the adhesioll alld cohesion characteristics of a mag­netic coating.
Adiabatic. Refers to conditions (usu­ally in speaker cabinates) where instantaneolls temperature rise due to air pressure changes occurs unimpeded.