2013 年 79 巻 799 号 p. 604-616
Arguably, noise suppression via active noise control is effective only within a fraction of the noise wavelength from an error sensor location. To expand the controllable region, it is a common practice to introduce the multi-channelization of a control system or sound power control of a noise source per se. It is also true, however, that they entail the following disadvantages: the multi-channelization causes complication, destabilization and increment of the computational burden; control sound sources need placing close enough to the noise source to achieve sound power control, hence impracticable. To overcome the disadvantages mentioned above, this paper presents a global active noise control method using a parametric array loudspeaker (PAL). Driving the ultrasonic transducers comprising PAL with a proper time delay enables one to produce the wavefront of control sound similar to that of noise, thereby suppressing a noise propagation in the vicinity of the noise source, resulting in the generation of a global zone of quite. The validity of the method presented is then clarified numerically as well as experimentally.