Method for extending the frequency range of a beamformer without spatial aliasing
View Patent ↗A conferencing unit, comprising an array of microphones embedded in a diffracting object configured to provide a desired high frequency directivity response at predetermined microphone positions, and a low frequency beamformer operable to achieve a desired low frequency directivity response, wherein the beamformer is linearly constrained to provide a smooth transition between low and high frequency directivity responses.
1. A method of extending the frequency range of a microphone array embedded in a diffracting object beyond a microphone spacing limitation of λ/2, where A =acoustic wavelength, comprising:
configuring said diffracting object to obtain a desired high frequency directivity response at predetermined microphone positions on said diffracting object;
providing a low frequency beamformer operable at said predetermined microphone positions to achieve a desired low frequency directivity response; and
applying linear constraints to said beamformer using two symmetrical look directions d θ−α and d θ+α with a gain constraint less than one and wherein the spacing θ−α and θ+α is controlled by α which increases with frequency, for providing a smooth transition between said low and high frequency directivity responses.
2. The method of claim 1 , comprising applying a thin layer of acoustic absorbent material to the surface of said diffracting object to absorb sound at high frequencies.
3. The method of claim 2 , wherein said acoustic absorbent material is applied between respective ones of said microphones.
4. The method of claim 3 , wherein said acoustic absorbent material is applied to a thickness of about λ/4 or higher to trap sound waves of wavelength λ.
5. A conferencing unit, comprising:
an array of microphones embedded in a diffracting object configured to provide a desired high frequency directivity response at predetermined microphone positions on said diffracting object; and
a low frequency beamformer operable at said predetermined microphone positions to achieve a desired low frequency directivity response, wherein said beamformer is linearly constrained using two symmetrical look directions d θ−α and d θ+α with a gain constraint less than one where the spacing θ+α and θ+α is controlled by α which increases with frequency.
6. The conferencing unit of claim 5 , further including a thin layer of acoustic absorbent material applied to the surface of said diffracting object to absorb sound at high frequencies.
7. The conferencing unit of claim 6 , wherein said acoustic absorbent material is applied between respective ones of said microphones.
8. The conferencing unit of claim 7 , wherein said acoustic absorbent material is applied to a thickness of about λ/4 or higher to trap sound waves of wavelength λ.
9. The conferencing unit of claim 6 wherein said acoustic absorbent material is one of either open cell foam or felt.
10. The conferencing unit of claim 5 , wherein said gain constraint is approximately 0.707.
11. A method of extending the frequency range of a wave sensor array embedded in a diffracting object beyond a inter sensor spacing limitation of λ/2, where λ=acoustic wavelength, comprising:
configuring said diffracting object to obtain a desired high frequency directivity response at predetermined sensor positions on said diffracting object;
providing a low frequency beamformer operable at said predetermined sensor positions to achieve a desired low frequency directivity response; and
applying linear constraints to said beamformer using two symmetrical look directions d θ−α and d θ+α with a gain constraint less than
one and wherein the spacing θ−α and θ+α is controlled by α which increases with frequency, for providing a smooth transition between said low and high frequency directivity responses.