This paper describes further investigations of an active noise control system in which an additional sound source is set close to the primary (noise) source. The synthesized sound radiated by the additional source is identical to that of the primary source, except in polarity. The additional and primary sources form a dipole sound source with reduced effective radiation power. In theory, the distance between these two sound sources should be less than the shortest wavelength in the required frequency range to realize an ideal dipole source. Then, the total sound pressure would be expected to attenuate in proportion to the square of the distance from the center of the sources, and little sound power would be radiated. However, in practice, the distance cannot be set small enough, so there is only a relatively small area around the dipole where the sound pressure attenuates in proportion to the square of the distance. Further afield, it attenuates in direct proportion to distance. Noise reduction is therefore limited. This paper describes the effects and the limits of performance of such a system as a function of wavelength and the dimensions of sound sources.
|Pages (from-to)||WA/NCA3 8p|
|Journal||American Society of Mechanical Engineers (Paper)|
|Publication status||Published - 1988|
|Event||Preprint - American Society of Mechanical Engineers - Chicago, IL, USA|
Duration: 1988 Nov 27 → 1988 Dec 2