Yoshitaka Nishimura

An adaptive algorithm with error path estimation for active control of periodic noise

When active noise control (ANC) systems are actually implemented, it is necessary to take account of the modeling error of an error path. The modeling error limits the performance of ANC and it makes the system unstable at worst. The characteristics of the error path cannot be assumed to be stable, so that on‐line estimation is preferred for actual applications such as an active control system of the exhaust noise of an engine. An adaptive algorithm called the delayed‐X harmonics synthesizer (DXHS) algorithm for periodic noise has been proposed. This algorithm controls amplitude and phase parameters for each harmonic component. The original algorithm controls parameters represented in polar coordinates with constant delay parameters. This paper presents an extended algorithm to estimate delay parameters of the error path on‐line. Delay parameters, which are important for the stability, are introduced as a phase, while other parameters are represented in orthogonal coordinates. The performance of the algor...

Application of a digital filter to active noise control in a duct

The possibility of active noise control and its frequency range are discussed using sound‐source impedance. When a digital filter is used in an active noise control system, the delay time required in the filter must be longer than those in AD‐DA converters and low‐pass filters. In order to make a two‐microphone active control system possible and to lower its frequency range, it is required that (1) the distance between the microphone set near the original source and the loudspeaker used for an additional source should be far; and that (2) the sampling frequency should be high. However, as the number of digital filter taps is fixed, there is a limitation on the sampling frequency in order to realize the characteristics in the low‐frequency range. In the proposed system with motional feedback, the active control is realized in a frequency range lower than the fundamental resonance frequency of the loudspeaker, f0. Thus f0 must be raised in order to realize a system at a higher frequency range.

An active noise control system by means of motional feedback without a microphone

A method for active noise control using a motional feedback system without any microphone is described. The impedance of an electroacoustic transducer can be controlled by motional feedback, and the noise in a duct can be reduced actively by adjusting the impedance of the transducer used for an additional sound source. The characteristics of the impedance of the transducer with the motional feedback and noise reducing effect of this system are analyzed, and they are measured using both analog filter implementation and a digital one. The results show that this system is effective in controlling the noise in a duct, but it is not applicable to a wide frequency range. The advantage of this system is that it does not need any microphone which has been a weak element in conventional active control systems under undesirable circumstances, such as high pressure, high temperature, dust, air flow, and so on.