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Claims  |
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What is claimed is:
1. Apparatus for the attenuation of sound from a source propagating in a
duct comprising:
input sensing means for detecting said source sound, said input sensing
means producing first electrical signals representing the amplitude and
phase characteristics of said source sound;
cancelling means for generating cancelling sound, said cancelling sound
being introduced into said duct for combination with and attenuation of
said source sound;
error sensing means for detecting said combination of said cancelling sound
and source sound, said error sensing means producing second electrical
signals representing the amplitude and phase characteristics of said
combination of said cancelling sound and source sound, the production of
said second electrical signals by said error sensing means being delayed
in time relative to the production of said first electrical signals by
said input sensing means due to the time of propagation of said source
sound from said input sensing means to said cancelling means and the time
of propagation of said source sound and cancelling sound to said error
sensing means; and
electronic controller means coupled to said input sensing means, cancelling
means and error sensing means for activating and controlling said
cancelling means to produce said cancelling sound, said electronic
controller means including an adaptive cancelling filter employing a
modified deterministic algorithm operable to accommodate said acoustic
propagation delays.
2. The apparatus of claim 1 wherein said input sensing means includes at
least one microphone.
3. The apparatus of claim 1 wherein said cancelling means is disposed in a
protective enclosure lined with acoustically absorbent material.
4. The apparatus of claim 1 wherein said cancelling means is disposed in a
protective enclosure lined with acoustically absorbant material.
5. The apparatus as in claim 1 wherein said acoustic propagation delays
include the time of propagation of said cancelling sound from said
cancelling means to said duct.
6. The apparatus as in claim 1 wherein said deterministic algorithm is a
modified least-mean-square algorithm.
7. Apparatus as in claim 1 further including waveguide means for connecting
said cancelling means to said duct, said cancelling sound being introduced
into said duct through said waveguide for combination with and attenuation
of said source sound
8. Apparatus as in claim 1 further including an acoustic mixer connected to
said duct at a location spaced from said input sensing means in the
direction of propagation of said source sound and forming a continuation
of said duct.
9. Apparatus as in claim 1 for the attenuation of sound from a source
propagating in a duct having a terminal end and a cross-sectional area
with a maximum transverse dimension, further including waveguide means for
connecting said cancelling means to said duct, said waveguide means being
spaced a distance at least three times said maximum transverse dimension
of said duct from said terminal end of said duct, said cancelling sound
being introduced into said duct through said waveguide for combination
with and attenuation of said source sound.
10. Apparatus as in claim 1 for the attenuation of sound from a source
propagating in a duct having a terminal end and a cross-sectional area
with a maximum transverse dimension, further including:
an acoustic mixer connected to said duct at a location spaced from said
input sensing means in the direction of propagation of said source sound
and forming a continuation of said duct; and
waveguide means for connecting said cancelling means to said acoustic
mixer, said waveguide means being spaced a distance at least three times
said maximum transverse dimension from said terminal end of said duct,
said cancelling sound being introduced into said duct through said
waveguide means for combination with and attenuation of said source sound.
11. Apparatus for the attenuation of sound from a source propagating in a
duct comprising:
input sensing means for detecting said source sound, said input sensing
means producing first electrical signals representing the amplitude and
phase characteristics of said source sound;
cancelling means for generating cancelling sound, said cancelling sound
being introduced into said duct for combination with and attenuation of
said source sound;
error sensing means for detecting said combination of said cancelling sound
and source sound, said error sensing means producing second electrical
signals representing the amplitude and phase characteristics of said
combination of said cancelling sound and source sound, the production of
said second electrical signals by said error sensing means being delayed
in time relative to the production of said first electrical signals by
said input sensing means due to the time of propagation of said source
sound from said input sensing means to said cancelling means and the time
of propagation of said source sound and cancelling sound to said error
sensing means; and
electronic controller means coupled to said input sensing means, cancelling
means and error sensing means for activating and controlling said
cancelling means to produce said cancelling sound, said electronic
controller means including an adaptive cancelling filter comprising a
transversal filter having a number of filter weights, said adaptive
cancelling filter employing an algorithm for adapting said weights in a
manner to accommodate said acoustic propagation delays.
12. Apparatus for the attenuation of sound from a source propagating in a
duct comprising:
input sensing means for detecting said source sound, said input sensing
means producing first electrical signals representing the amplitude and
phase characteristics of said source sound;
cancelling means for generating cancelling sound,
a pair of waveguide means for connecting said cancelling means with said
duct, said waveguide means being connected parallel to and on opposite
sides of said duct at a location spaced from said input sensing means in
the direction of propagation of said source sound, said waveguide means
introducing said cancelling sound into said duct in the direction of
propagation of said source sound for combination with said source sound
thereby preventing the first cross mode of said source sound from
developing in said duct;
error sensing means for detecting said combination of said cancelling sound
and source sound, said error sensing means producing second electrical
signals representing the amplitude and phase characteristics of said
combination of said cancelling sound and source sound, the production of
said second electrical signals by said error sensing means being delayed
in time relative to the production of said first electrical signals by
said input sensing means due to the time of propagation of said source
sound from said input sensing means to said cancelling means and the time
of propagation of said source sound and cancelling sound to said error
sensing means; and
electronic controller means coupled to said input sensing means, cancelling
means and error sensing means for activating and controlling said
cancelling means to produce said cancelling sound, said electronic
controller means including an adaptive cancelling filter employing a
modified deterministic algorithm operable to accommodate said acoustic
propagation delays.
13. Apparatus for the attenuation of sound from a source propagating in a
duct comprising:
input sensing means for detecting said source sound, said input sensing
means producing first electrical signals representing the amplitude and
phase characteristics of said source sound;
cancelling means for generating cancelling sound;
a pair of waveguide means for connecting said cancelling means to said
duct, said waveguide means being connected perpendicular to said duct and
in alignment with one another on opposite sides of said duct to provide
paths for propagation of said cancelling sound to said duct for
combination with said source sound, thereby preventing the first cross
mode of said source sound from developing in said duct;
error sensing means for detecting said combination of said cancelling sound
and source sound, said error sensing means producing second electrical
signals representing the amplitude and phase characteristics of said
combination of said cancelling sound and source sound, the production of
said second electrical signals by said error sensing means being delayed
in time relative to the production of said first electrical signals by
said input sensing means due to the time of propagation of said source
sound from said input sensing means to said cancelling means and the time
of propagation of said source sound and cancelling sound to said error
sensing means; and
electronic controller means coupled to said input sensing means, cancelling
means and error sensing means for activating and controlling said
cancelling means to produce said cancelling sound, said electronic
controller means including an adaptive cancelling filter employing a
modified deterministic algorithm operable to accommodate said acoustic
propagation delays.
14. Apparatus for the attenuation of sound from a source propagating in a
duct comprising:
input sensing means for detecting said source sound, said input sensing
means producing first electrical signals representing the amplitude and
phase characteristics of said source sound;
cancelling means for generating cancelling sound, said cancelling sound
being introduced into said duct for combination with and attenuation of
said source sound;
error sensing means for detecting said combination of said cancelling sound
and source sound, said error sensing means producing second electrical
signals representing the amplitude and phase characteristics of said
combination of said cancelling sound and source sound, the production of
said second electrical signals by said error sensing means being delayed
in time relative to the production of said first electrical signals by
said input sensing means due to the time of propagation of said source
sound from said input sensing means to said cancelling means and the time
of propagation of said source sound and cancelling sound to said error
sensing means; and
an electronic controller, coupled to said input sensing means, cancelling
means and error sensing means, including an adaptive cancelling filter, an
amplifier, a phase correction filter and DC loop means, said adaptive
cancelling filter employing a modified deterministic algorithm operable to
accommodate acoustic propagation delays for the production of an output,
said amplifier receiving said output and driving said cancelling means for
the production of said cancelling sound, said phase correction filter
adjusting the phase characteristics of said second electrical signal
produced by said error sensing means and said DC loop means providing a DC
signal for introduction into said adaptive cancelling filter to assure
stable operation thereof.
15. Apparatus for the attenuation of sound from a source propagating in a
duct comprising:
input sensing means for detecting said source sound, said input sensing
means producing first electrical signals representing the amplitude and
phase characteristics of said source sound;
cancelling means for generating cancelling sound, said cancelling sound
being introduced into said duct for combination with and attenuation of
said source sound;
error sensing means for detecting said combination of said cancelling sound
and source sound, said error sensing means producing second electrical
signals representing the amplitude and phase characteristics of said
combination of said cancelling sound and source sound, the production of
said second electrical signals by said error sensing means being delayed
in time relative to the production of said first electrical signals by
said input sensing means due to the time of propagation of said source
sound from said input sensing means to said cancelling means and the time
of propagation of said source sound and cancelling sound to said error
sensing means; and
an electronic controller, coupled to said input sensing means, cancelling
means and error sensing means, including an adaptive cancelling filter, an
amplifier, a phase correction filter and DC loop means, said adaptive
cancelling filter comprising a transversal filter having a number of
filter weights, said adaptive cancelling filter employing an algorithm for
adapting said weights in a manner to accommodate said acoustic propagation
delays for the production of an output, said amplifier receiving said
output and driving said cancelling means for the production of said
cancelling sound, said phase correction filter adjusting the phase
characteristics of said second electrical signals produced by said error
sensing means and said DC loop means providing a DC signal for
introduction into said adaptive cancelling filter to assure stable
operation thereof.
16. Apparatus for the attenuation of sound from a source propagating in a
duct comprising:
input sensing means for detecting said source sound, said input sensing
means producing first electrical signals representing the amplitude and
phase characteristics of said source sound;
cancelling means for generating cancelling sound, said cancelling sound
being introduced into said duct for combination with and attenuation of
said source sound, said cancelling sound producing at least some standing
waves propagating in the opposite direction of said source sound, said
standing waves being detectable by said input sensing means and being
incorporated into said first electrical signals representing the amplitude
and phase characteristics of said source sound within said duct;
error sensing means for detecting said combination of said cancelling sound
and source sound, said error sensing means producing second electrical
signals representing the amplitude and phase characteristics of said
combination of said cancelling sound and source sound, the production of
said second electrical signals by said error sensing means being delayed
in time relative to the production of said first electrical signals by
said input sensing means due to the time of propagation of said source
sound from said input sensing means to said cancelling means and the time
of propagation of said source sound and cancelling sound to said error
sensing means; and
an electronic controller including an adaptive uncoupling filter, an
adaptive compensation filter and an adaptive cancelling filter, said
adaptive uncoupling filter being operable to substantially remove the
component of said first electrical signals produced by said input sensing
means representing said standing waves generated by said cancelling sound
and sensed by said input sensing means, said adaptive compensation filter
being operable to adjust the phase characteristics of said second
electrical signals produced by said error sensing means for introduction
into said adaptive cancelling filter to assure stable operation thereof,
said adaptive cancelling filter employing a modified deterministic
algorithm operable to accommodate said acoustic propagation delays for the
production of an output for activating and controlling said cancelling
means to produce said cancelling sound.
17. Apparatus for the attenuation of sound from a source propagating in a
duct comprising:
input sensing means for detecting said source sound, said input sensing
means producing first electrical signals representing the amplitude and
phase characteristics of said source sound;
cancelling means for generating cancelling sound, said cancelling sound
being introduced into said duct for combination with and attenuation of
said source sound, said cancelling sound producing at least some standing
waves propagating in the opposite direction of said source sound, said
standing waves being detectable by said input sensing means and being
incorporated into said first electrical signals representing the amplitude
and phase characteristics of said source sound within said duct;
error sensing means for detecting said combination of said cancelling sound
and source sound, said error sensing means producing second electrical
signals representing the amplitude and phase characteristics of said
combination of said cancelling sound and source sound, the production of
said second electrical signals by said error sensing means being delayed
in time relative to the production of said first electrical signals by
said input sensing means due to the time of propagation of said source
sound from said input sensing means to said cancelling means and the time
of propagation of said source sound and cancelling sound to said error
sensing means; and
an electronic controller including an adaptive uncoupling filter, an
adaptive compensation filter and an adaptive cancelling filter, said
adaptive uncoupling filter being operable to substantially remove the
component of said first electrical signals produced by said input sensing
means representing said standing waves generated by said cancelling sound
and sensed by said input sensing means, said adaptive compensation filter
being operable to adjust the phase characteristics of said second
electrical signals produced by said error sensing means for introduction
into said adaptive cancelling filter to assure stable operation thereof,
said adaptive cancelling filter comprising a transversal filter having a
number of filter weights, said adaptive cancelling filter employing an
algorithm for adapting said weights of said transversal filter to
accommodate said acoustic propagation delays for the production of an
output to activate and control said cancelling means for generating said
cancelling sound.
18. Apparatus for the attenuation of sound from a source propagating in a
duct comprising:
input sensing means for detecting said source sound, said input sensing
means producing first electrical signals representing the amplitude and
phase characteristics of said source sound;
cancelling means for generating cancelling sound;
a pair of waveguide means for connecting said cancelling means with said
duct, said waveguide means being connected parallel to and on opposite
sides of said duct at a location spaced from said input sensing means in
the direction of propagation of said source sound, said waveguide means
introducing said cancelling sound into said duct in the direction of
propagation of said source sound for combination with said source sound
thereby preventing the first cross mode of said source sound from
developing in said duct, said cancelling sound producing at least some
standing waves propagating in the opposite direction of said source sound,
said standing waves being detectable by said input sensing means and being
incorporated into said first electrical signals representing the amplitude
and phase characteristics of said source sound within said duct;
error sensing means for detecting said combination of said cancelling sound
and source sound, said error sensing means producing second electrical
signals representing the amplitude and phase characteristics of said
combination of said cancelling sound and source sound, the production of
said second electrical signals by said error sensing means being delayed
in time relative to the production of said first electrical signals by
said input sensing means due to the time of propagation of said source
sound from said input sensing means to said cancelling means and the time
of propagation of said source sound and cancelling sound to said error
sensing means; and
an electronic controller including an adaptive uncoupling filter, an
adaptive compensation filter and an adaptive cancelling filter, said
adaptive uncoupling filter being operable to substantially remove the
component of said first electrical signals produced by said input sensing
means representing said standing waves generated by said cancelling sound
and sensed by said input sensing means, said adaptive compensation filter
being operable to adjust the phase characteristics of said second
electrical signals produced by said error sensing means for introduction
into said adaptive cancelling filter to assure stable operation thereof,
said adaptive cancelling filter employing a modified deterministic
algorithm operable to accommodate said acoustic propagation delays for the
production of an output for activating and controlling said cancelling
means to produce said cancelling sound.
19. Apparatus for the attenuation of sound from a source propagating in a
duct comprising:
input sensing means for detecting said source sound, said input sensing
means producing first electrical signals representing the amplitude and
phase characteristics of said source sound;
cancelling means for generating cancelling sound;
a pair of waveguide means for connecting said cancelling means with said
duct, said waveguide means being connected perpendicular to said duct in
alignment with one another on opposite sides of said duct to provide paths
for propagation of said cancelling sound to said duct for combination with
said source sound to prevent the first cross mode of said source sound
from developing in said duct, said cancelling sound producing at least
some standing waves propagating in the opposite direction of said source
sound, said standing waves being detectable by said input sensing means
and being incorporated into said first electrical signals representing the
amplitude and phase characteristics of said source sound within said duct;
error sensing means for detecting said combination of said cancelling sound
and source sound, said error sensing means producing second electrical
signals representing the amplitude and phase characteristics of said
combination of said cancelling sound and source sound, the production of
said second electrical signals by said error sensing means being delayed
in time relative to the production of said first electrical signals by
said input sensing means due to the time of propagation of said source
sound from said input sensing means to said cancelling means and the time
of propagation of said source sound and cancelling sound to said error
sensing means; and
an electronic controller including an adaptive uncoupling filter, an
adaptive compensation filter and an adaptive cancelling filter, said
adaptive uncoupling filter being operable to substantially remove the
component of said first electrical signals produced by said input sensing
means representing said standing waves generated by said cancelling sound
and sensed by said input sensing means, said adaptive compensation filter
being operable to adjust the phase characteristics of said second
electrical signals produced by said error sensing means for introduction
into said adaptive cancelling filter to assure stable operation thereof,
said adaptive cancelling filter employing a modified deterministic
algorithm operable to accommodate said acoustic propagation delays for the
production of an output for activating and controlling said cancelling
means to produce said cancelling sound.
20. Apparatus for the attenuation of sound from a source propagating in a
duct comprising:
input sensing means for detecting said source sound, said input sensing
means producing first electrical signals representing the amplitude and
phase characteristics of said source sound;
cancelling means for generating cancelling sound, said cancelling sound
being introduced into said duct for combination with and attenuation of
said source sound, said cancelling sound producing at least some standing
waves propagating in the opposite direction of said source sound, said
standing waves being detectable by said input sensing means and being
incorporated into said first electrical signals representing the amplitude
and phase characteristics of said sound within said duct;
error sensing means for detecting said combination of said cancelling sound
and source sound, said error sensing means producing second electrical
signals representing the amplitude and phase characteristics of said
combination of said cancelling sound and source sound, the production of
said second electrical signals by said error sensing means being delayed
in time relative to the production of said first electrical signals by
said input sensing means due to the time of propagation of said source
sound from said input sensing means to said cancelling means and the time
of propagation of said source sound and cancelling sound to said error
sensing means; and
an electronic controller including an adaptive uncoupling filter, an
adaptive compensation filter, an adaptive cancelling filter, DC loop means
for introducing a DC signal to said adaptive cancelling filter, and low
pass filter means for limiting the frequency range of said first and
second electrical signals within said electronic controller, said adaptive
uncoupling filter being operable to substantially remove the component of
said first electrical signals produced by said input sensing means
representing said standing waves generated by said cancelling sound and
sensed by said input sensing means, said adaptive compensation filter
being operable to adjust the phase characteristics of said second
electrical signals produced by said error sensing means for introduction
into said adaptive cancelling filter to assure stable operation thereof,
said adaptive cancelling filter employing a modified deterministic
algorithm operable to accommodate said acoustic propagation delays for the
production of an output for activating and controlling said cancelling
means to produce said cancelling sound.
21. An apparatus as in claim 20 wherein said low pass filter means provide
an inherent processing delay in the function of said electronic controller
in addition to said acoustic propagation delays, whereby to accommodate
said delays the physical spacing between said input sensing means,
cancelling means and error sensing means must be in accordance with the
following relationship:
T>.lambda.min/4+d.sub.1 +d.sub.2 +D.sub.F
wherein
T=spacing between microphone array and error microphone
.lambda.min=shortest wavelength of interest in the source sound
d.sub.1 =spacing between the speaker and acoustic mixer
d.sub.2 =spacing between the waveguide and error microphone
D.sub.f =delay associated with the low pass filters. |
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Claims |
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