An active acoustic power control method for three-dimensional space was investigated both theoretically and experimentally. In this paper, the focus is on the typical case of a single primary and two secondary point sources, and methods of minimizing the power output were considered. Suitable arrangements of the sources and microphone were proposed on the basis of theoretical estimations. The authors call this the acoustic nodal point method. The power reducing performance was verified by applying the method to the noise radiating from a duct opening.

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This paper attempts to improve the performance of ear-plug type earphones. The transmission characteristics of the ear canal with/without earphones are different. Therefore, the sound quality of the earphone is a little poor compared with audio speaker. In addition, it is well-known that the acoustical characteristics of ear canal vary among individuals. Therefore, we are studying to predict the acoustical characteristics of ear canal with ear-plug type earphones by using transfer matrix method and are studying how to improve the transmission characteristics of the ear canal. In this paper, a method for adjusting the resonance characteristic of the ear canal with earphones to the characteristic of the ear canal of AV speakers without earphones using digital filtering technique is proposed. With this method, the improvement of the sound reproduction performance was verified on the basis of experiments.

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