Active minimization of acoustic power for a multipole noise source in free space

Abstract

Low-frequency noise is difficult to be suppressed by passive control using sound absorbing materials. Active noise control is expected to be an effective method against low-frequency noise. Minimizing the total acoustic power emitted by a sound source causes a zero-control power phenomenon. In the zero-control power phenomenon, the absorption and blowout of sound energy around the control sound source (control sound source) are balanced, and the time average of the control power comes into zero. Thus, control power suppression may be used to for minimize of total acoustic power. Previous studies have assumed that the sound source is a monopole sound source, or a piston embedded in an infinite baffle, so there are restrictions on the sound source. In this research, the noise sound sources are regarded as a multi-pole sound source. Numerical computations are performed based on the derived control law to clarify the effect of the position and the rotation angle of the multi-pole source on the acoustic power. In addition, the relationship between the wavelength and the suppression effect is examined from a numerical point of view.