Damping for directional sound cancellation
First Claim
1. Apparatus for the directional reduction of sound, comprisingfirst and second electrically driven sound sources for positioning in the path of sound to be reduced with the first source nearer to the source of the said sound than the second source,signal-generating means for generating a drive signal to drive the first source, andprocessing means for so processing the drive signal and applying it to drive the second source that sound generated by the first and second sources tends to be in phase at all frequencies of interest on that side of the second source which is remote from the first source, andthe signal-generating means and the processing means being such that the resultant generated sound on the said side of the second source tends to be in anti-phase with sound to be cancelled at all the said frequencies.
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Accused Products
Abstract
Sound in ducts can be reduced by using two cancelling sources spaced along the duct, and in order to reduce reflections upstream of the cancelling sources, sounds from these sources may be arranged to be in phase opposition upstream from the sources at all frequencies. Such an arrangement does not provide cancellation downstream at some frequencies. In the invention sound detected by a microphone is processed to generate a drive signal for a first source which tends to cancel sound in the duct partially, the remainder of the cancellation being provided by a sound source. A delay positioned between the sources is such that sounds from these sources are in phase at all frequencies of interest downstream of the second source.
38 Citations
12 Claims
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1. Apparatus for the directional reduction of sound, comprising
first and second electrically driven sound sources for positioning in the path of sound to be reduced with the first source nearer to the source of the said sound than the second source, signal-generating means for generating a drive signal to drive the first source, and processing means for so processing the drive signal and applying it to drive the second source that sound generated by the first and second sources tends to be in phase at all frequencies of interest on that side of the second source which is remote from the first source, and the signal-generating means and the processing means being such that the resultant generated sound on the said side of the second source tends to be in anti-phase with sound to be cancelled at all the said frequencies.
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11. A method for the directional reduction of sound comprising generating first and second sound waves at first and second positions respectively in the path of sound to be reduced, with the first position nearer to the source of the said sound than the second position, the first and second sounds being, or tending to be, in phase at all frequencies of interest on that side of the second position which is remote from the first position and the resultant generated sound wave tending to be in anti-phase at all frequencies of interest with sound to be cancelled on the said side of the second position.
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12. Apparatus for the directional reduction of sound, comprising
first and second electrically driven sound sources for positioning in the path of sound to be reduced with the first source nearer to the source of the said sound than the second source, signal-generating means for generating a drive signal to drive the first source, and processing means for so processing the drive signal and applying it to drive the second source that sound generated by the first and second sources tends to be in phase at all frequencies of interest on that side of the second source which is remote from the first source, and the signal-generating means and the processing means being such that the resultant generated sound on the said side of the second source tends to be in anti-phase with sound to be cancelled at all the said frequencies, said signal generating means including a detector for detecting the sound to be reduced, the detector being positioned among the said sources of the apparatus, said detector being coupled by way of means having a transfer function TD to the input of the first source to provide the said drive signal, and TD is equal to -1/(1-e-2iω - τ
), where i is √
-1, ω
is angular frequency and τ
is delay imparted by the processing means.
- τ
Specification