U.S. patent application number 11/403573 was filed with the patent office on 2006-11-09 for adaptive personal active noise system.
Invention is credited to William R. Saunders, Michael A. Vaudrey.
Application Number | 20060251266 11/403573 |
Document ID | / |
Family ID | 25312838 |
Filed Date | 2006-11-09 |
United States Patent
Application |
20060251266 |
Kind Code |
A1 |
Saunders; William R. ; et
al. |
November 9, 2006 |
Adaptive personal active noise system
Abstract
An improved active noise reduction system which has a
transducer, an electro-acoustic sensing means including adjacent to
the transducer, an attenuation means with electro-acoustic sensing
means to attenuate selected sound frequencies, said system
utilizing both feed forward control means and feedback control
means comprising a heteronomous electronic controller with
algorithmic transfer function and said controller being
individually operable.
Inventors: |
Saunders; William R.;
(Blacksburg, VA) ; Vaudrey; Michael A.;
(Blacksburg, VA) |
Correspondence
Address: |
ROBERTS, MARDULA & WERTHEIM, LLC
11800 SUNRISE VALLEY DRIVE
SUITE 1000
RESTON
VA
20191
US
|
Family ID: |
25312838 |
Appl. No.: |
11/403573 |
Filed: |
April 13, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09534730 |
Mar 27, 2000 |
7110551 |
|
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11403573 |
Apr 13, 2006 |
|
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08852245 |
May 6, 1997 |
6078672 |
|
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09534730 |
Mar 27, 2000 |
|
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Current U.S.
Class: |
381/71.1 |
Current CPC
Class: |
G10K 11/17881 20180101;
G10K 2210/3222 20130101; H04R 1/1083 20130101; G10K 2210/30351
20130101; G10K 2210/3025 20130101; G10K 2210/3026 20130101; G10K
2210/3016 20130101; G10K 2210/511 20130101; G10K 2210/3027
20130101; G10K 2210/3219 20130101; G10K 2210/506 20130101; G10K
2210/3042 20130101; G10K 2210/10 20130101; G10K 2210/3033 20130101;
G10K 2210/3214 20130101; G10K 2210/128 20130101; G10K 2210/1282
20130101; G10K 2210/108 20130101; G10K 2210/3046 20130101; G10K
2210/101 20130101; G10K 2210/1081 20130101; G10K 2210/3056
20130101; G10K 2210/1082 20130101; G10K 2210/3031 20130101; G10K
2210/3221 20130101; G10K 11/17854 20180101; G10K 11/17857 20180101;
G10K 2210/3217 20130101 |
Class at
Publication: |
381/071.1 |
International
Class: |
A61F 11/06 20060101
A61F011/06; G10K 11/16 20060101 G10K011/16; H03B 29/00 20060101
H03B029/00 |
Claims
1. A heteronomous controller of a personal active noise attenuation
system comprising: a feedback controller adapted for receiving an
acoustically transduced signal from a noise error sensor and for
generating a feedback active noise attenuating control signal
portion; a feedforward controller adapted for: receiving the
acoustically transduced signal from the noise error sensor;
receiving a noise reference signal from a noise reference signal
sensor; and applying an adaptive signal processing algorithm to the
acoustically transduced signal from the noise error sensor and to
the noise reference signal to generate an adaptive active noise
attenuation control signal portion; and a linear combiner adapted
for summing a linear combination of the feedback active noise
attenuating control signal portion and the adaptive active noise
attenuation control signal portion so as to generate a heteronomous
control signal.
2. The heteronomous controller of claim 1 further comprising a
compensator adapted for canceling a feedback path from the noise
reference signal sensor before application of the adaptive signal
processing algorithm, wherein the feed forward controller receives
the noise reference signal from the noise reference signal sensor
via the compensator
3. The heteronomous controller of claim 2, wherein the feedback
compensator is an analog filter.
4. The heteronomous controller of claim 2, wherein the compensator
is a digital filter.
5. The heteronomous controller of claim 1, wherein the adaptive
signal processing algorithm is an adaptive feedforward
algorithm.
6. The heteronomous controller of claim 1, wherein the adaptive
signal processing algorithm is an adaptive feedback algorithm.
7. The compensator of claim 2, wherein the compensator is executed
on the feedforward controller that executes the adaptive signal
processing algorithm.
8. The compensator of claim 2, wherein the feedforward controller
is further adapted for minimizing a sensitivity of a loop transfer
function between the acoustically transduced signal from the noise
error sensor and the adaptive active noise attenuating control
signal portion of the heteronomous control signal.
9. The heteronomous controller of claim 1, wherein the noise error
sensor is a microphone.
10. The heteronomous controller of claim 1, wherein the noise error
sensor is an accelerometer.
11. The heteronomous controller of claim 1, wherein the noise error
sensor is spatially adaptable in the noise field.
12. The heteronomous controller of claim 1, wherein the noise
reference signal sensor is a microphone.
13. The heteronomous controller of claim 1, wherein the noise
reference signal sensor is an accelerometer.
14. The heteronomous controller of claim 1, wherein the noise
reference signal sensor is the noise error sensor.
15. The heteronomous controller of claim 1, wherein the noise
reference signal sensor is spatially adaptable in the noise
field.
16. The heteronomous controller of claim 1, wherein the personal
active noise attenuation system is a headset system comprising a
head-mounting portion, earcups, a noise error sensor, a noise
reference signal sensor, and an electroacoustic control speaker
system.
17. The heteronomous controller of claim 1, wherein the personal
active noise attenuation system is a silent seat comprising a noise
error sensor, a reference signal sensor, and an electroacoustic
control speaker system.
18. The heteronomous controller of claim 1, wherein the linear
combiner is an analog summing amplifier.
19. The heteronomous controller of claim 1, wherein the linear
combiner is adapted for proportionally combining the feedback
active noise attenuation control signal portion and the adaptive
active noise attenuation control signal portion in the feed forward
controller.
20. The heteronomous controller of claim 1, where the linear
combiner summer is adapted for outputting selectively controlled
proportions of the feedback active noise attenuation control signal
portion and the adaptive active noise attenuation control signal
portion.
21. The heteronomous controller of claim 1, wherein the personal
active noise attenuation system is a headset and earplug system
comprising a head mounting portion, earcups, and earplugs, further
comprising a noise error sensor, a noise reference signal sensor,
and an electroacoustic control speaker system.
22. The heteronomous controller of claim 1, wherein the personal
active noise attenuation system is an earplug system comprising
earplugs, a noise error sensor, a noise reference signal sensor,
and an electroacoustic control speaker system.
23. The heteronomous controller and earplug system of claim 22
where earplugs are custom earmolds, foam earplugs, flanged
earplugs, acrylic earplugs.
24. The heteronomous controller of claim 23, wherein the
electroacoustic control speaker system is comprised of one or more
speakers.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 09/534,730, which is a divisional of U.S. application Ser. No.
08/852,245, filed May 6, 1997, now U.S. Pat. No. 6,078,672. The
U.S. application Ser. No. 09/534,730, the U.S. application Ser. No.
08/852,245 and the U.S. Pat. No. 6,078,672 are each incorporated by
reference herein, in their entirety, for all purposes.
BACKGROUND
[0002] This invention is related to an improved personal noise
attenuation system which can be employed to attenuate noise
observed by users in sound fields containing objectionable noise.
The invention can be employed on headsets, silent seats and other
personal applications such as an automotive radius headliner and
trim package.
[0003] Most active noise control systems utilize acoustic drivers
in conjunction with acoustic sensors, controller(s) and associated
signal conditioning electronics to reduce preselected sound
pressure levels from impinging upon the ear drum. The instant
invention is in the form of a personal system which may take the
form of a headset, a "silent seat" (one designed to attenuate sound
pressures at the users ears when the user is occupying the chair)
or other form of personal quieting system. For example, the instant
system can be employed as part of the headliner in an automobile
for the purpose of attenuating road, engine or other designated
noise. The instant invention overcomes the current limitations of
existing devices by the use of spatial adaptation of an acoustic
error sensor and implementation of a unique heteronomous control
algorithm. Additionally, the user has increased comfort in the
headset configuration by use of non-contacting electroacoustic
transducers
[0004] The field of active noise cancellation has progressed from
the simple attempts in the 1970s by Chaplin in the United Kingdom
to attenuate noise to todays more complex systems which are geared
to specific types of noises. The field of noise cancellation has
been reviewed extensively in "Active Control of Sound" by P. A.
Nelson and S. J. Elliot, Academic Press, 1991. Progress in
attenuating tonal noise has included the development of digital
virtual earth systems which use fewer sensors than heretofore
employed (see U.S. Pat. No. 5,105,377 to Ziegler et al entitled
"Digital Virtual Earth Active Cancellation System". Cancellation of
unwanted broadband noise has seen development of adaptive
feedforward systems which measure the noise prior to its arrival at
the cancellation point. In some applications these systems have
been combined to attenuate a mixture of objectionable noises. By
the use of frequency domain algorithms control over the
characteristics of the noise cancellation has been achieved and
these algorithms have been further modified by harmonic filters in
constant rate sampling of sound converting time domain signals into
frequency domain signals (see U.S. Pat. No. 5,361,303 to Eatwell
entitled "Frequency Domain Adaptive Control System"). Adaptive
speech filters have enhanced all of the prior art attempts at noise
attenuation and/or cancellation by measuring the spectrum of the
data and blocking any frequencies that do not exhibit statistical
properties of standard speech thereby allowing speech in noisy
environments.
[0005] The use of adaptive filtering techniques is widespread today
and characterized by the controller characteristics being adjusted
according to an algorithm such as that disclosed by Widrow and
Stearns, "Adaptive Signal Processing", Prentice Hall, 1985. Both
feedback systems (see U.S. Pat. No. 4,494,074 to Bose entitled
"Feedback Control") and feedforward systems (see U.S. Pat. Nos.
4,122,303 and 4,654,871, both to Chaplin and U.S. Pat. No.
4,878,188 to Ziegler) have been used before in personal quieting
systems. Adaptive filtering techniques are discussed in the patents
to Graupe (has U.S. Pat. No. 5,097,510) and Graupe and et al (U.S.
Pat. No. 4,025,721).
[0006] Despite the large amount of development in the personal
quieting system area, the instant invention has not been conceived
of by others in the field. No one heretofore has shown or described
the simultaneous use of feedback and adaptive signal processing
algorithms (heteronomous control) to target different features of
the noise field. Nor are there any prior patents or disclosures
describing the use of a spatially adaptable error microphone based
on the changing dimensions of the silent zone in different noise
fields.
[0007] It has been suggested to incorporate both asynchronous
feedback and microphone-based feedback compensation cancellation
techniques into a single system. The attenuation concept discussed
by Casalli (J. G. Casalli and G. S. Robinson, "Narrow-Band Digital
Active Noise Reduction include In a Siren-Cancelling Headset:
Real-Ear and Acoustical Manikin Insertion Loss", Noise Control
Engineering Journal, 42 (3), 1994, May/June, page 101.) but no
system has been built or developed. Casalli refers to a
siren-canceling headset not unlike the one described in U.S. Pat.
No. 5,375,174 to Denenberg entitled "Remote Siren Headset" which is
hereby incorporated by reference herein. The architecture that the
article suggests is totally different from that of the instant
invention and nowhere in the article does it suggest adaptive
positioning of the noise microphone. There is no discussion in the
article or elsewhere of using a remote microphone for a blended
feedforward/feedback architecture.
[0008] There have been endless variations on the noise cancelling
headset over the years including those disclosed by Wadsworth in
U.S. Pat. No. 3,098,121, Chaplin et al, in U.S. Pat. No. 4,654,871,
Twiney et al, in U.S. Pat. No. re 4,953,217, Bourk in U.S. Pat. No.
5,182,774 and Nishimoto et al, in U.S. Pat. No. 5,402,497, all of
which are hereby incorporated by reference herein. The use of
circumaural headsets dominates the ANR headset market due to the
lower actuator demand in the quiet enclosure afforded by earmuffs.
While there are supraural headsets the instant device
differentiates from them by being open-air thus affording no
confinement whatsoever of the user's ears. The open air system
requires controlling a higher level of sound pressure and wider
variance as there is no confinement by the muffs, whether supraural
or circumaural.
[0009] Various systems to affix earpieces to headgear have been
proposed which those shown in U.S. patents to Altman and Goldfarb
et al, U.S. Pat. Nos. 5,329,592 and 4,682,363, respectively, both
of which are hereby incorporated by reference herein.
[0010] Remote control of headsets has been suggested as evidenced
by U.S. patents to Schwab and Hsiao-Chung Lee, U.S. Pat. Nos.
4,845,751 and 4,930,148, respectively.
[0011] A review of the current status of active noise control
headsets illustrates the advantages of the invention. The vast
majority of active noise headsets employ either feedback
compensation, as in the Bose et al patent, or adaptive signal
processing algorithms, as described in U.S. Pat. No. 5,375,174 to
Denenberg, implemented in time domain or frequency domain format.
These two distinctive architectures have unique characteristics
especially in relation to one another. Feedback control relies on a
compensator to maximize the sensitivity function within the
stability bounds specific to the particular noise field under
consideration and active noise hardware in use. This arrangement
results in a reduction in the closed-loop, low frequency gain
between the disturbance input (the surrounding noise field) and the
output signal (the error microphone). Noise relief realized by this
technique is typically between 15 to 20 dB re 20 microPa and can be
achieved from approximately 50 to 700 Hz. These limitations on
noise reduction and performance bandwidth cannot be overcome for
reasons that are documented by experts in the active acoustic
control community. In this regard see also U.S. Pat. No. 5,251,263
to Andrea et al, entitled "Adaptive Noise Cancellation and Speech
Enhancement System and Apparatus Therefore".
[0012] Adaptive feedforward noise reduction for personal ANR
systems has also been proposed but to a much lesser extent. Such an
architecture relies on the availability of a reference signal which
is correlated with the estimate of the noise field and cannot be
destabilized by the control signal. Such references have been
constructed for the case of periodic inputs (see Chaplin et al)
such as a reciprocating pump or propeller which can be used to
spawn synchronous reference signals which serve as inputs to the
adaptive filter. The other approach is to provide a compensator
which cancels the feedback path between a so-called controllable
reference signal and the control signal, e.g., the filtered-u
algorithm. The degree of noise suppression for adaptive feedforward
systems is a direct function of the multiple coherence (between the
constructed, or otherwise available, reference signal and the
acoustic sensor which will be minimized) dB reduction=20
log.sub.10(1-.gamma..sup.2)
[0013] The performance bandwidth is limited by the sampling
frequency for the digital filter and the size of the adaptive
filter but can practically achieve noise reductions into the kHz
range. Theoretically, this approach can provide up to 50 dB
suppression of noise levels and more than triple the feedback
control bandwidth of the feedback methods.
[0014] The architecture of the essential components in any personal
ANR system also has profound influence on the absolute and
user-perceived performance of the system. Existing active noise
control headsets and systems are designed using fixed spatial
separations between the electroacoustic transducers and the
acoustic sensor near the listener's ear(s). Recent theoretical and
experimental results have proven that the spatial dimension of the
noise field reductions is a nonlinear function of the noise
frequency, the electroacoustic transducer, and the separation
distance between an electroacoustic transducer surface and the
acoustic sensor being controlled. The silent zone spatial dimension
is relatively small for typical headset components/geometries and
varies with the noise frequency (FIG. 1). For a fixed frequency,
the silent zone dimension varies with separation distance between
the acoustic sensor and the driver (FIG. 2). This variability of
the silent zone's spatial and temporal characteristics has not been
properly exploited in any existing designs for personal ANR
systems.
[0015] The prior art in personal ANR technology has reached an
impasse imposed by the tradeoffs which currently exist for the
available architectures. Feedback control headsets can provide
robust noise reductions, nominally 15 dB from 50 Hz to 700 Hz, but
do not require the identification or generation of an
uncontrollable reference signal. Adaptive feedforward headsets can
achieve substantially higher noise reductions, particularly at
tonal disturbances, but must have a correlated, uncontrollable
reference signal available. Both types use fixed relative
positioning between the electroacoustic driver, the acoustic error
sensors, and the listener's eardrum. More specifically, the prior
art fails to combine the features of both architectures in a single
personal ANR system and fails to exploit the nonlinear dependencies
of the silent zone created around by the suppression of a single
error microphone. Headsets produced in the past such as the
"Proactive" and "Noisebuster" headsets of Noise Cancellation
Technologies, Inc. as well as those of Sennheiser, David Clark and
Bose fail to contemplate the features constituting this
invention.
[0016] While all the prior art discussed above relates to personal
ANR systems, they are limited by lack of performance in noise
fields dominated by broadband and tonal disturbances. Furthermore,
they fail to optimize the perceived effectiveness, as perceived by
the user, by providing real-time or psuedo real-time adaptation of
the relative positioning of the ANR components. Therefore, the
following invention embodies heteronomous control and adaptive
spatial positioning of the ANR components, along with an open air
arrangement so as to surpass the prior art in performance and
comfort for the user.
SUMMARY
[0017] It is a main purpose of this invention to provide for
optimal noise reduction capabilities in a personal ANR system for a
variety of noise fields without compromising the wearer's comfort.
By linearly combining the advantages of two diverse control
algorithms, exploiting the changing physical characteristics of
spatial silent zones in different noise fields and considering the
user's comfort, a non-contact, fully adaptable heteronomous
controlled personal ANR system becomes a major advance over the
prior art. It is noteworthy that no portion of this improved system
need come into contact with the user's head or ears. Normal
communication remains unencumbered and the ergonomics of user
comfort is no longer an issue. The system can be adapted to fit any
existing headgear including formal hats, helmets, hard-hats, casual
hats, sports headgear of both a protective nature as well as
decorative and any other device or mechanism designed to be worn on
the head or body of a user, i.e., the improved ANR system forming
this invention is application independent. Since it is adapted to
be selectively positioned by the user it is infinitely
adaptable.
[0018] The control algorithm used herein is a heteronomous
feedback/feedforward approach. The common feedback compensator is
not presented as the primary means of control but rather a method
for dealing with inadequacies of the adaptive feedforward algorithm
thus complementing each other. The feedforward compensator method
is robustly stable in the proposed architecture and thus has the
capability of very high levels of noise reduction which can reach
up to but not limited to 50 dB for tonals in certain cases. The
controller can select the individual or combined operation of the
two controllers based on the noise field measured by the
suppression microphone. It is further understood that the feedback
controller may be implemented in analog or digital embodiments
while the feedforward filters are implemented in digital
embodiments for typical noise fields but may be constructed in
analog hardware for noise fields with low dimensionality.
[0019] Feedforward noise control mandates a coherent reference
signal and a system identification of the transfer function
existing between the controller output and the error signal
terminus. Typically this is called filtered reference, filtered-u,
or filtered-x algorithm, i.e., the error signal is the actual
microphone signal. The control output of the algorithm is summed
with the control output of the feedback controller (either
digitally or with an analog summing amplifier depending on the
nature of the feedback controller) and sent through the control
speaker. The system identification of the control to error path for
the filtered-x algorithm is done ahead of time and stored in the
DSP ROM therefore eliminating the requirement for system ID.
[0020] The feedback controller is a loop shaped design which
maximizes the loop gain of the controller in the frequency range of
interest, typically 100 to 1000 Hz. Limitations on plant dynamics
do not permit a higher frequency range to be explored. Typical
feedback controllers in these devices are effected through analog
hardware, which is one preferred embodiment of this controller
architecture. However, the feedback controller can be included in
the control software to eliminate another hardware expense.
Selectivity can be manual or a frequency sensitive switch can be
incorporated therein to switch the system to the most efficient
mode for the type of noise being attenuated.
[0021] In accordance with this invention the arrangement of the
control actuator/acoustic-electric sensor combination with respect
to the subject's head offers not only comfort but several unique
performance advantages. With the acoustic-electric sensor located
within the radius of reverberation of the electro-acoustic
actuator, the system identification used in the filtered-x version
of the feedforward control remains nearly constant for relatively
significant changes in the acoustic-electric sensor positions. Such
an arrangement allows for an adaptable acousto-electric sensor
placement to maximize the silent zone reaching the wearer's ear. A
tradeoff in the size of the silent zone exists between the location
of the error acoustic-electric sensor with respect to the
electric-acoustic actuator (either manual or deterministically
automatic) shall be adaptable for frequency dependent disturbances.
This is a unique feature allowing optimal performance of this
system in a given environment. In addition to adapting the position
of the acoustic-electric sensors with respect to the control
actuator, the control actuator is also adaptable with respect to
the listener's head. This provides an added measure of comfort and
performance thus allowing the user to maximize the zone of silence
near the eardrum.
[0022] A primary advantage of the instant invention is its ability
to reduce tonal and narrowband noises by significantly larger
margins than the existing headset technologies due to the
heteronomous approach. Another primary advantage is the recognition
that the error microphone location is critically important to the
perceived performance by the user. This phenomena is realized by
the changing spatial silent zones which are created when a point
pressure sensor is minimized within the radius of reverberation of
a secondary speaker thus minimizing spatial spillover potential,
reducing power output required of the secondary speaker, minimizing
the phase delay and achievement of the highest possible stability
margins for a closed loop controller.
[0023] Accordingly, it is an object of this invention to provide an
ANR system which allows a wearer to maximize the zone of silence
near his eardrum(s).
[0024] Another object of this invention is to provide an ANR system
in which all the components are adjustable relative to the
user.
[0025] It is another object of this invention to provide an ANR
system with an electricacoustic sensor which is adaptable for
frequency dependant disturbances.
[0026] It is yet another object of this invention to provide an ANR
headset which has positionable sensors adapted to exploit the
changing physical characteristics of spatial silent zones in
different noise fields.
[0027] Furthermore, it is an object of this invention to provide an
ANR headset with open-air sensors which do not confine the users
movements or ears.
[0028] Still another object of this invention is to provide optimal
noise reduction in a personal ANR headset without sacrificing
wearer comfort.
[0029] Yet another object of this invention is to provide an ANR
headset which is adapted to fit within a wide range of headgear
worn by a user.
[0030] Another object of this invention is to provide an ANR system
having an algorithmic control utilizing a feedback/feedforward
heteronomous approach.
[0031] A further object of the invention involves providing an ANR
system which can operate in purely feedforward mode or a
feedforward combined with feedback mode, or feedback mode only.
[0032] These and other objects will become apparent when reference
is had to the accompanying drawings.
DESCRIPTION OF THE FIGURES
[0033] FIG. 1 is a graph plotting frequency versus width of zone of
silence depicting the dimensions of the silent zone's nonlinear
dependence on the frequencies suppressed by the controller for
fixed electroacoustic transducer radius and microphone separation
distance.
[0034] FIG. 2 shows two three dimensional plots depicting the
changes with frequency of the spatial areas of silence about error
microphones for a given position away from the control speaker.
[0035] FIGS. 3 and 3a represent the adaptive personal ANR system
depicted in only one of many possible embodiments, in this case a
helmet adaptation and specific embodiments of the adaptable
positioning system, respectively.
[0036] FIG. 4 is a block diagram showing the general structure for
the heteronomous controller and signal paths used in attenuating
the objectionable noise arriving at the user's ear canal.
[0037] FIG. 5 is a block diagram showing only the feedforward
portion of the heteronomous controller.
[0038] FIG. 6 is a block diagram showing only the feedback portion
of the heteronomous controller from FIG. 1.
[0039] FIG. 7 is a block diagram schematic showing the existence of
cross paths between the left and right side transducers and
actuators.
[0040] FIG. 8 is a block diagram which shows the individual
components of the heteronomous, adaptable positioning ANR
system.
[0041] FIG. 9 is a plot illustrating the amount of reduction
achieved at the left ear using only the feedforward portion of the
heteronomous controller for a five tonal noise field.
[0042] FIG. 10 illustrates the control exercised by the feedback
portion of the heteronomous system for a broadband noise field.
[0043] FIG. 11 illustrates the control achieved by the heteronomous
controller on a noise field containing both broadband and tonal
content.
[0044] FIG. 12 is a block diagram showing the overall ANR
system.
DETAILED DESCRIPTION
[0045] A detailed description of all of the preferred system
structures and overall intended embodiments of the adaptive
personal ANR system are now explained by reference to the figures.
The description commences with an explanation of the unique physics
which motivate one aspect of the apparatus followed by a discussion
of the various embodiments which have been conceived and/or
developed for the architecture.
[0046] Referring to FIG. 3 the adaptable personal ANR system is
shown consisting of two electro-acoustic actuators 1R and 1L, a
pair of acoustic-electric transducers 2R, 2L, a mounting apparatus
and means for adjusting the relative and absolute positions of the
actuators and transducers 4R, 4L, 5R and 5L.
[0047] As seen in FIG. 3, each of the right and left
electric-acoustic actuators 1R and 1L are adjustably affixed to the
mounting apparatus 3 by means G.sub.AP (4R and 4L) which permits
movement of the actuator with respect to the user's ear and with
respect to the mounting apparatus. This feature is included in
order to allow various sized users to wear the apparatus
comfortably and maximize the reduction of objectionable noise
arriving at the user's eardrum. The actuators are mounted to 3 in a
manner in which there is no portion of the actuator touching the
users head but rather "floating" on the mount away from the user's
ear. At no point during the operation will any portion of the
actuator or transducer contact the user's head or ear thereby
leaving normal communication and hearing acuity intact apart from
any passive noise reduction measures. The headgear 3 has been
designed with several degrees of freedom for the wearer in order to
optimize performance with respect to the user's perception of
sound. To facilitate this there is movement of the control speakers
with respect to the wearer's ears (in and out, front and back),
movement of the error microphone with respect to the wearer's ear
canal and limited relative movement of the microphone with respect
to the control speaker. The headgear will accommodate different
size heads. The controller hardware and reference signal required
by the feedforward controller can be located remotely (from the
user) while the control speakers and error microphones can be
located on the user. Communications between these devices requires
two separate two-way channels, one each for receiving the control
signal and one each for sending the microphone signals. Such an
arrangement minimizes the "load" on the user insofar as hardware is
concerned. Alternatively, the control hardware can be loaded on the
user and requires a single one-way line wireless communication to
the hardware on the user.
[0048] The size of the zone of silence around the microphone
created by the control speaker is a function of frequency,
decreasing in size with higher frequency. Depending on the
characteristics of the noise field the user can adjust the position
of the microphone with respect to his or her own hearing to
maximize the sound reduction that is actually heard. No existing
ANR headgear show this feature.
[0049] Several overall system structures or embodiments are
realized in varying levels of wireless data communication and
remote battery powered operation or also powered via a tethered
line supplying power. FIG. 3 illustrates the first (and second)
structures wherein the first utilizes a non-tethered wireless data
transmission and receiver system one mounted to 3 mounting
apparatus 6 and one remote data transmission and receiver system 7
which transmits two transducer signals from 2R and 2L and receives
two actuator signals driving 2R and 2L wherein the digital signal
processor and control hardware (8 located adjacent to 7 not mounted
on 3) are also remote and not mounted to 3. The second embodiment
removes 8 from the remote location adjacent to 7 and affixes it to
the mounting apparatus 3 in that the only signal which will be
transmitted is from the objectionable noise source to 7 in a
wireless manner to 6 and received by 8. The digital signal
processor in both embodiments 8 requires signals from 2R and 2L and
9 and provides signals for actuators 1R and 1L. The signal from the
disturbing acoustic noise 9 is to be coherent with the acoustic
disturbance arriving at each of the transducers 2R and 2L as
mandated by the feedforward portion of the heteronomous control law
now presented.
[0050] Each of the right and left side acoustic-electric
transducers 2R (L) are adjustable mounted directly onto the
electric-acoustic actuators 1R (L). The transfer function 5R (L)
G.sub.EP represents the adaptable position of the error microphone
which when 9 mounted directly to 1R (L) is affected by either a
manual positioning system using a gear train which restrains the
microphone to an amount of travel in which the electric-acoustic to
acoustic-electric transfer function remains nominally unchanged or
an automated motor driven system commanded by a manual input dial
or a fully automated motor driven system which calculates the
optimal position of the transducer 2R (L) with respect to the noise
field, the position of the transducer relative to the actuator, and
the position of the transducer relative to the eardrum. Referring
to FIG. 3a these three embodiments are illustrated at 5R (A, B and
C) in the close-up views of the overall apparatus. The
electro-acoustic actuator is adjustably mounted via 10R (L)
including front, back, up, down, in, out, and rotationally with
respect to the wearer in order to accommodate many sized heads and
ear positions. The acoustic-electric transducer stator (mount 11)
is adjustably affixed to 1R (L) via 12 (a set screw) which allows
movement rotationally about screw 12 in the plane of the wearer's
ear to ultimately adjust the position of the sensor 2R (L) given
the user's desire for optimal noise reduction and comfort.
[0051] The rack and pinion system used for positioning the sensor
in the sense that it is closer or farther from the wearer's ear
canal consists of the housing 13, the rack 14, and the pinion gear
internal to the housing which is driven and controlled in one of
three possible manners detailed in 5R (A, B, and C). 5R (A) details
the manual dial 15 used to rotate the pinion gear which drives the
rack and positions the sensor 2R (L). This embodiment provides the
user with direct control over the position of the microphone
affording the possibility of maximum user-perceived noise reduction
within the constraints of the control algorithm 5R (B) replaces the
manual dial 15 with a very small DC motor 16 which instead drives
the pinion of 5R (A) but may be more readily adjustable since the
dial 18 can be located in a more ergonomically feasible location.
Finally, the illustration in 5R (B) can be further modified as in
5R (C) to replace the user selectability with an algorithm which
maximizes the field of silence surrounding the sensor depending on
the sensor's location from the transducer 1R (L) and the general
character of the noise field. For example, a predominantly low
frequency noise field sensed by 2R (L) will result in 19 commanding
the motor 16 to move the rack (and thus the sensor) to/from the
transducer to maximize the silent zone around the microphone. The
drawback of this approach is that no user interaction is
facilitated and may result in a slightly less than optimal noise
reduction perceived at the eardrum.
[0052] The user selectable embodiments of this apparatus 5R (A and
B) rely on loudness feedback from the user's perception of the
noise field to be cancelled and are therefore optimal for reduction
of loudness experienced by the user. Affixing 2R and 2L directly to
1R and 1L by aforementioned means G.sub.EP, adjustment relative to
the actuator and the eardrum is affected based on the position of
the actuator. Both embodiments require restricted movement of the
transducer with respect to the actuator for reasons involving a
stable system identification of the actuator to transducer transfer
function as well as maintaining the location of the transducer
within the radius of reverberation of the actuator thereby
permitting a minimal power control force imparted by the
actuator.
[0053] FIG. 4 represents the system architecture for the
heteronomous controller resident on the digital signal processor 8
while FIGS. 5 and 6 extract the individual feedforward and feedback
controller portions of the control system. FIG. 5 shows the
adaptive feedforward controller portion of the heteronomous control
system which utilizes either the conventional LMS algorithm or a
modified version termed as the leaky LMS algorithm 31 which uses a
tap delay line weight update equation preventing overflow in
limited precision hardware platforms conforming to:
w(n+1)=(1-.mu..alpha..)w(n)+.mu.V.sub.out(n)r(n)
[0054] which updates the self designing FIR filter H.sub.ff 26 by
using a filtered 30 input signal r and the transducer signal
V.sub.out to create a controller which minimizes the mean square of
the V.sub.out signal. The filtered input signal conforms to the
common filtered-x algorithm for noise control where the input must
be filtered by an estimate of the transducer function existing from
the actuator output to the acoustic-electric transducer because the
output of the controller itself does not act directly upon the
disturbance d and thus must be taken into account before control
commences. Since the acoustic-electric transducer is located and
constrained to remain within the radius of reverberation of the
control actuator, the transfer function estimate of the filtered-x
algorithm does not significantly change with changing relative
position and thus can be fixed and saved in the digital signal
processor memory prior to control eliminating the need for
continual update of the estimate. The transfer function is
identified for all frequencies within the control bandwidth and
thus is specified independent of the nature of the disturbance
signal.
[0055] Proceeding through FIG. 5 the input r to the feedforward
controller is first low pass filtered 25 for anti-aliasing purposes
and used in the update of the weights 31 of the FIR filter as well
as filtered by the adaptive feedforward transfer function H.sub.ff
26 whose output is smoothed using another low pass filter 27 whose
output experiences the electric-acoustic transducer transfer
function 28 and the acoustic path 29 traveling to the
acoustic-electric transfer function which is also dynamically
located via aforementioned means and is exposed to the
objectionable noise d from some physical disturbance 20 originating
from some source s wherein the input of the feedforward controller
r is coherent with s. The output of the acoustic electric
transducer 21 is conditioned to remove low and high frequency
content beyond the controller bandwidth using both a low pass and
high pass filter means 32 and 33.
[0056] Feedforward control typically does well when controlling
tonal content and can generally eliminate the noise at the error
microphone and maintain stability. Conversely, feedback control can
effectively eliminate broadband sound up to 25 dB in some frequency
ranges.
[0057] FIG. 6 shows the portion of the heteronomous controller
which is considered to derive strictly from feedback control
theory. The undesirable disturbance signal d is the same as which
is shown in FIG. 4 and FIG. 5 for the feedforward controller and
the acoustic-electric transfer function also receives sound
pressure from the feedback control actuation force applied through
23 which is the same actuator as in the feedforward controller
although labeled 28. The output signal from the acoustic-electric
transducer 21 is used as the feedback signal for the compensation
H.sub.fb 22 which is designed in order to perform a rejection of
the disturbance noise thereby increasing the gain of 22 while
maintaining appropriate stability margins which will minimize the
sensitivity function of the feedback system. The output of the
controller drives the control actuator which is also being driven
by the feedforward controller thus 28 and 23 are the same actuator
in the heteronomous controller for a single side, right or
left.
[0058] FIG. 7 illustrates the paths which exist (34 and 35) between
the right side actuator 1R, the left side transducer 2L as well as
between the left side actuator 1L and the right side transducer 2R.
In performing both the feedforward and feedback control actions
these paths are taken into account with respect to each other 36 so
as to prevent positive feedback and instabilities in the overall
system.
[0059] To summarize thus far, the heteronomous controller is used
to reduce the objectionable sound power reaching the user's ears.
The central summing junction represents the overall sound power
incident on the acoustic-electric transducer from the heteronomous
controller which includes both the feedback and feedforward control
algorithms as well as the undesirable sound power d reaching the
user's ears and the cross path terms from 34 and 35. It is
emphasized that control actuation and acoustic paths shown as 23
and 24 are also represented as the control actuator and acoustic
paths used in the feedforward portion of the control scheme
therefore in effect the output signal of 22 and the output signal
of 27 are linearly combined prior to driving the electric-acoustic
actuator but are shown separately in order to clarify the two
control schemes. The feedforward controller is capable of achieving
tonal control (shown in FIG. 9) with extreme authority (up to 50
dB) due to its robustly stable design but becomes increasingly
incapable for broadband noise fields having large frequency ranges
of control which in turn requires large filter sizes and
computational overhead. Feedback control offers less overall
reduction but provides broadband noise control (FIG. 10) for wide
frequency ranges. Summing the control forces from each of these
methods results in a robustly stable controller capable of
suppressing very colorful noise fields including high amplitude
tonals as well as moderate broadband noise fields. FIG. 11 shows
this arrangement.
[0060] FIG. 8 illustrates two embodiments of the controller design.
An impinging sound pressure level is transduced by a microphone
subject to a control input from the adaptable positioning system.
The adaptable positioning system is realized using apriori
information about the ANR components and information from the DSP
processor in regards to the spectral content of the sound field.
The microphone signal goes through the data acquisition components
(anti-aliasing filter, sample-hold circuit, and analog-to-digital
converter.) and is processed by the DSP. A feedforward and feedback
control signal exits the DSP block. The feedforward controller is a
digital filter by design can be realized in one of two possible
ways. The first is via analog hardware represented by a fixed
design operational amplifier circuit or designed in conjunction
with the feedforward controller manifested as a fixed design
digital IIR filter operating at the same sample rate as the
feedforward controller. FIG. 8 illustrates the digital
implementation.
[0061] Again referring to FIG. 8 the heteronomous control effect is
evidenced in the acoustic-electric transducer output V.sub.out
which can be shown to consist of a unique combination of
compensation means described by V out = G mic 1 + G mic .times. G
ac .times. G sp .times. H fb .times. d + G mic .times. G ac .times.
G sp .times. H ff 1 + G mic .times. G ac .times. G sp .times. H fb
.times. r ##EQU1##
[0062] Consequently, the heteronomous ANR performance can be
considered as an adaptive compensation of the residual signal
created by the feedback controller, as identified originally. A
corresponding reduction in the spectral norm of the
cross-correlation matrix between the reference input signal r and
the error signal V.sub.out results in a significant advantage for
the convergence characteristics of the adaptive portion as compared
to prior art. Stability of the converged heteronomous ANR system is
determined solely by the H.sub.fb design.
[0063] The user of the instant invention can determine whether he
wished to employ the feedback only, adaptive feedforward only or
the combined system for reduction of both tonals and
broadbands.
[0064] FIG. 10 shows the SPL versus frequency plot using feedback
only in the headset system while FIG. 11 shows the SPL versus
frequency plot for the heteronomous operation of headset system.
FIG. 12 shows an overall block diagram view of the device showing
the various inputs, components and interaction there between. Note
that the heteronomous control processor feeds the DSP and Analog
compensators which produce output to the ANR component hardware.
Feedback from hardware flows back to the heteronomous control
processor which compares it with an ambient acoustic noise input as
well as a user perceived loudness input. The user adjusts the
adaptable positioning control which optimizes the system to the
user.
[0065] The above recital of the operation of the system can be
enhanced by a review of the following articles: "Active Control of
Sound and Vibration", by C. R. Fuller and A. R. vonFlotow, IEEE
Control Systems, December 1995, pp 9-19, "A Hybrid Structural
Control Approach for Narrowband and Impulsive Disturbance
Rejection", by W. R. Saunders, H. H. Robertshaw and R. A. Burdisso,
Noise Control Engineering Journal, Special Issue on Active Noise
Control, Vol. 44, No. 1, January-February, 1996; and "Active Noise
Control Systems: Designing for the Auditory System", by W. R.
Saunders and M. A. Vaudrey, Proceedings of Noise-Con 96, Bellevue,
Wash., September 1996. Each of these articles is incorporated
herein by reference.
[0066] Having described the invention it is readily apparent that
many changes and modifications thereto may be made by those of
ordinary skill in the acoustic arts without departing from the
scope of the appended claims.
* * * * *