Frequency dependent acoustic beam forming and nulling

Broadly, this invention resides in apparatus and methods involving a set of soundfield nulling algorithms providing a localized decrease in sound intensity. Among the benefits of the approach, is that there is little, if any, affect on other important positions such as power or spectral content, insofar as energy is directed to unimportant areas. In the preferred embodiment, two separate algorithms are used, depending upon the frequency range of the acoustic signal. For lower frequencies (for example, less than 300 Hz), the algorithm is based on Cepstral techniques and overtly uses the fact that in an enclosed area, the predominant acoustic influence is in the form of standing waves. At higher frequencies, however, (i.e., 300 Hz and above), the sound is due to free-space propagation. Consequently, single free-space algorithms that are applied across the spectrum have great difficulty in providing useful sound nulls without distortion.