Acoustic characteristics and cancellation performance of a basic free-field noise cancellor

摘要

A unique theory for generating electronically controlled acoustic shadows for environmental noise reduction was reported in (1). The theory has been extended to complex high frequency sound from large non-compact sources in (1.2). The implementation of the theory into hardware is considered in (1.3). Practical extensions to the theory are considered in (1.4). the effect of environmental change is considered in (1.5) and the fundamental cancelling system considered in (1.6). Before the sound cancellation performance of multichannel freefield cancelling systems could be evaluated in detail, it was considered prudent to establish first the characteristics of a single channel system. The shadow characteristics are computed and compared with examples of measured performance. Good agreement is obtained, which can now be used to validate the far field sound cancellation predictions.