Three-dimensional Global Active Noise Control Using a Delayed Driving Parametric Array Loudspeaker

In general, conventional active noise control is effective only within a fraction of the wavelength from an error sensor. To expand this region, multi-channelization of system and/or reduction of radiation power of noise sources can be considered; however, these two methods have disadvantages. Multi-channelization often causes complication, destabilization and increment of the computational burden. On the other hand, it is necessary for suppressing the acoustic radiation power to set up the control sound source within a half wavelength from the noise source. However it may be difficult to implement it in a practical case. This paper presents a global active noise control method for three-dimensional sound field that compensates these disadvantages. Parametric Array Loudspeaker (PAL) in which multiple ultrasonic transducers are placed concentrically is introduced as the control sound source. Driving the ultrasonic transducers with proper time delays, the control sound source produces the wavefront similar to the noise away from the noise source. Superposing the control sound on the original noise sound, and suppressing the sound pressure at the error sensor, sound pressure is suppressed over a wide area around the error sensor. The validity of the proposed method is clarified from a viewpoint of numerical simulations.