2.3. Are there different kinds of active control?
Description
This article is from the Active Noise Control FAQ, by Dr. Chris Ruckman
2.3. Are there different kinds of active control?
There are two basic approaches for active noise control: active noise cancellation (ANC) and active structural-acoustic control (ASAC). In ANC, the actuators are acoustic sources (speakers) which produce an out-of-phase signal to "cancel" the disturbance. Most people think of ANC when they think of active noise control; some examples are mentioned below. On the other hand, if the noise is caused by the vibration of a flexible structure, then ASAC may be more appropriate than ANC. In ASAC, the actuators are vibration sources (shakers, piezoceramic patches, etc.) which can modify how the structure vibrates, thereby altering the way it radiates noise. (The distinction between ANC and ASAC is somewhat arbitrary, since both cases correspond to a controller using actuators to reduce the plant response.)
Active vibration control is a related technique that resembles active noise control. In either case, electromechanical actuators control the response of an elastic medium. In active noise control, the elastic medium is air or water through which sound waves are traveling. In active vibration control, the elastic medium is a flexible structure such a satellite truss or a piece of vibrating machinery. The critical difference, however, is that active vibration control seeks to reduce vibration *without* regard to acoustics. Although vibration and noise are closely related, reducing vibration does not necessarily reduce noise.
Actually, you can generate your own catchy phrases with the following handy buzzword generator. Simply choose one word from each column, string them all together without commas, and paste the result or its acronym into your document or conversation!
/ Column A \ / Column B (optional) \ / Column C \ | ----------- | | ------------------- | | ------------ | | active | | vibration | | cancellation | < adaptive > < noise > < control > | semi-active | | sound | | damping | | | | structural-acoustic | | suppression | \ / \ vibro-acoustic / \ /
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