Frequency dependent acoustic beam forming and nulling
First Claim
1. A method of soundfield nulling, comprising the steps of:
- designating a transition frequency or region below which there are lower frequencies to be nulled, and above which there are higher frequencies to be nulled;
canceling the lower frequencies using a first algorithm that considers standing waves; and
canceling the lower frequencies using a second algorithm that considers free-space propagation.
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Accused Products
Abstract
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.
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Citations
13 Claims
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1. A method of soundfield nulling, comprising the steps of:
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designating a transition frequency or region below which there are lower frequencies to be nulled, and above which there are higher frequencies to be nulled;
canceling the lower frequencies using a first algorithm that considers standing waves; and
canceling the lower frequencies using a second algorithm that considers free-space propagation. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. Sound field nulling apparatus, comprising:
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an input for receiving an audible signal to be nulled;
frequency-based filtering to separate out lower and higher frequencies from the audible signal;
a processor operative to apply first and second sound-cancellation algorithms to the lower and higher frequencies; and
an output for generating an acoustical signal based upon the result. - View Dependent Claims (10, 11, 12, 13)
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Specification