Feedback Controller Optimization for Active Noise Control Headphones Considering Frequency Response Mismatch between Microphone and Human Ear

Fengyan An,Qianqian Wu,Bilong Liu

doi:10.3390/app12030977

Abstract

This paper presents an investigation on the feedback controller design for active noise control headphones under the condition that the frequency responses of the primary and secondary paths corresponding to the feedback microphone do not match to the ones corresponding to the human ear. The influence of such mismatches on the performance are analyzed first, and then an optimization method is proposed to enhance the comprehensive performance at the human ear. In the proposed method, the feedback loop is constructed directly with the feedback microphone and any extra filters of the virtual sensing techniques are avoided. Cascade biquad filters are used as the controller, which is in accordance with current applications. A differential evolution algorithm was used to solve the proposed optimization problem, and the optimal parameters of the controller were found. It has been shown by the experimental results that, at the dummy head ear position, good noise reduction performance could be obtained at the low frequency band with limited noise enhancement for high frequencies, even if large frequency response mismatches exist.

Highlights

Wireless headphones have become one of the most prevailing wearable personal devices in recent years
Within low frequency band where the active noise control (ANC) system is expected to be effective, the frequency response (FR) mismatch has a fatal influence on the noise reduction (NR) performance and should be avoided at the acoustic design stage of the headphones
Large FR mismatches at high frequencies could lead to significant noise enhancement for the human ear even if it is well constrained for the feedback microphone

Summary

Introduction

Wireless headphones have become one of the most prevailing wearable personal devices in recent years. For most high-qualified headphones, an active noise control (ANC) module is generally equipped as a standard configuration, which is designed to reduce the outside noise and offer a better listening environment. The control strategies for ANC headphones can be classified into the feedforward, the feedback and the hybrid ones, among which the feedback control strategy has the longest history of research and application and is discussed in the rest of this paper. In feedback ANC headphones, the noise reduction (NR) within the low frequency band is generally realized at the price of noise enhancements at other frequencies, which is well-known as the waterbed effect [1] in the literature. The basic principle to design a feedback controller for ANC headphones is to maximize the NR performance within the low frequency band while maintain the robust stability of the system and restricting the noise enhancement at high frequencies. The NR bandwidth is restricted by the delay of the open-loop plant response [1], which indicates that the feedback microphone should be placed near the speaker and the latency of the controller should be minimized

Methods

Results

Conclusion