U.S. patent number 3,770,911 [Application Number 05/273,943] was granted by the patent office on 1973-11-06 for hearing aid system.
This patent grant is currently assigned to Industrial Research Products, Inc.. Invention is credited to Elmer Victor Carlson, Hugh Shaler Knowles.
United States Patent |
3,770,911 |
Knowles , et al. |
November 6, 1973 |
**Please see images for:
( Certificate of Correction ) ** |
HEARING AID SYSTEM
Abstract
A hearing aid system for providing improved and adjustable
directivity.
Inventors: |
Knowles; Hugh Shaler (Elgin,
IL), Carlson; Elmer Victor (Prospect Heights, IL) |
Assignee: |
Industrial Research Products,
Inc. (Elk Grove Village, IL)
|
Family
ID: |
23046079 |
Appl.
No.: |
05/273,943 |
Filed: |
July 21, 1972 |
Current U.S.
Class: |
381/313;
381/327 |
Current CPC
Class: |
G02C
11/06 (20130101); H04R 1/38 (20130101); H04R
25/402 (20130101) |
Current International
Class: |
G02C
11/00 (20060101); G02C 11/06 (20060101); H04R
25/00 (20060101); H04R 1/38 (20060101); H04R
1/32 (20060101); G02c 011/06 () |
Field of
Search: |
;179/107,121D |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Blakeslee; Ralph D.
Claims
What is claimed is:
1. A hearing aid including a housing, a directional microphone in
said housing, said microphone having at least two spaced sound
ports, said housing having at least two spaced sound openings,
means for acoustically coupling said sound openings to respective
ones of said sound ports, and means for adjustably varying the
effective acoustical delay between said sound ports for determining
the directivity of said hearing aid.
2. A hearing aid as in claim 1 wherein said sound openings and
sound ports are in longitudinal spaced relation to form relative
front and rear openings and front and rear sound ports, and means
are provided for varying the separation between said sound
openings.
3. A hearing aid as in claim 2 further including an acoustical
chamber in said housing, means for mounting said microphone in said
chamber to separate said chamber into a front cavity and a rear
cavity, the front sound opening communicating with the front cavity
and the front sound port; and, the rear sound opening communicating
with the rear cavity and the rear sound port.
4. A hearing aid as in claim 2 wherein said microphone is mounted
to provide a front cavity region and a back cavity region in said
chamber, a passageway connecting said front and rear cavity
regions, and means for selectively restricting said passageway
whereby said chamber acoustically changes from functioning as a
single cavity to functioning as two separate cavities thereby to
determine the directional characteristics of the hearing aid.
5. A hearing aid as in claim 4 wherein said means for selectively
restricting said passageway is a vane mounted in said passageway,
said vane being rotatable from a first or open position to a second
or closed position to restrict and close said opening.
6. A hearing aid as in claim 4 further including means attached to
said vane and extending outwardly of the hearing aid housing for
manually selecting the position of the said vane.
7. A hearing aid including an acoustical chamber in said housing, a
microphone mounted in said housing, said microphone having an
acoustical cavity and having relative front and rear sound ports
coupling to the cavity, said housing having spaced sound openings
in relative front and rear positions, said rear sound port
providing an acoustical phase shift, and means for adjustably
changing the effective acoustical phase shift thereof to thereby
determine the directivity of said hearing aid.
8. A hearing aid as in claim 7 wherein said microphone includes a
plurality of sound ports, and means for selectively closing said
sound ports to determine the directivity of the hearing aid.
9. A hearing aid as in claim 7 wherein means are provided for
mounting said microphone in said chamber, and means for changing
the volume of the microphone cavity to change the directivity of
said hearing aid.
10. A hearing aid as in claim 7 wherein said means for adjustably
changing the acoustical phase shift comprises means for changing
the size of said
opening responsive inversely to the barometric pressure. 11. A
hearing aid as in claim 9 further including a plate, bellows means
positioning said plate adjacent said rear opening, said bellows
means being responsive to barometric pressure to thereby change the
position of said plate relative to said rear port to thereby change
the acoustical impedance of said rear
port. 12. A hearing aid as in claim 9 further including a plate
mounted in said cavity, said plate connected to a movable member,
resilient expandable affixed to said cavity and expandable as said
plate is moved in said cavity, said member being manually
positionable to vary the position of said plate in said cavity and
hence the effective size of said cavity
to thereby vary the directivity of the hearing aid. 13. A hearing
aid including a housing having an acoustical chamber therein, a
directional microphone mounted in said chamber, said microphone
having at least two spaced sound ports, said housing having at
least two spaced sound openings, means for acoustically and
selectively coupling said openings to said sound ports, and means
for varying the spacing between the sound openings to provide an
effective acoustical spacing different from the spacing between
said sound ports to thereby vary the directivity of the
hearing aid. 14. A hearing aid as in claim 13 wherein the
orientation of the minimal response sensitivity of the hearing aid
may be determined by
the orientation and relative separation of the sound openings. 15.
A hearing aid as in claim 13 further including a first tube
connecting one of said openings to one of said sound ports and a
second tubing for connecting the other of said openings to the
other of said sound ports.
A hearing aid as in claim 15 wherein a first opening faces a
frontal direction and a second opening faces in an upward
direction, and means for adjusting the position of said second
tubing to thereby adjustably vary
the distance between the two openings. 17. A hearing aid as in
claim 13 wherein said microphone is mounted in said chamber to form
a front and a rear cavity, means for adjusting the separation
between the openings to
thereby determine the directivity of said hearing aid. 18. A
hearing aid as in claim 13 including a series of longitudinally
spaced openings, and means for selectively closing said openings to
vary the directivity of said hearing aid.
Description
BACKGROUND OF THE INVENTION
In the prior art, most hearing aids worn on the head, including
aids mounted or worn behind the ear, hearing aids mounted on eye
glasses and hearing aids mounted in the ear lack satisfactory
directivity.
Prior art microphones used in hearing aids commonly have
non-directional response characteristics; and, people who wear
hearing aids often find that the hearing aid does not give them any
adequate indication as to the relative direction of the source of
sound. Because of the non-directional characteristics of the
hearing aid and microphone combination, a wearer may realize
various problems. One example is the case where a number of persons
are involved in a discussion and several of them are talking at the
same time, in which case the wearer may find it difficult to detect
the source of each particular sound. In contrast to the foregoing,
a person wearing a hearing aid with directional characteristics is
afforded the advantage of sensing the direction of the source of
sound so that he may turn his head in the direction of the source;
and, he can preferentially pick out or distinguish the source of
that particular sound while detection of the source of sound is
aided by his visual sense.
Accordingly, various efforts have heretofore been made to provide
directivity in hearing aids. However, for one reason or another,
such prior art devices have not been entirely satisfactory. For
example, some of such prior devices are highly sensitive to noise
and to undesired amplified sounds which are objectionable to the
wearer. Such undesired amplified sounds which reach the microphone
in the hearing aid tend to be reamplified and produce whistling
sounds which become quite annoying to the wearer.
The problem of obtaining satisfactory directional response is
further complicated when a person who is hard of hearing in both
ears wears a hearing aid for one ear only. Or, the degree of
deafness of each ear of a wearer of a hearing aid is not equal;
that is, the wearer may hear better through one ear then he can
through the other ear.
Also, as is known, the human head distorts the normal sound
patterns, such that a person who wears a hearing aid mounted on one
side of the head hears a sound coming from that side louder or more
distinctly than the sound coming from the other side of the
head.
Thus, since the auditory requirements of each wearer varies, it is
highly desirable to provide a hearing aid with adjustable
directivity enabling the user to adjust or alter the directivity to
position the sound reception or rejection angle at an optimum for
his use.
Accordingly, it is a principal object of the present invention to
provide a hearing aid in which the directivity is adjustable for
changing the direction of maximum and minimum relative
sensitivity.
The foregoing and other features and advantages of the invention
will be apparent from the following more particular description as
illustrated in the accompanying drawings wherein:
FIG. 1 is a drawing useful in explaining the operation of the
invention;
FIGS. 2(a)-2(e) show various polar pattern responses useful in
explaining the inventive apparatus;
FIG. 3 is a drawing illustrating an eyeglass-mounted hearing aid
useful in explaining important features of the invention;
FIGS. 4(a) and 4(b) depict the top of a human head and show a
head-mounted hearing aid for purposes of explaining the response
balancing concept of the invention;
FIG. 5 is an isometric view of an embodiment of the invention
wherein the spacing or distance between the hearing aid housing
openings is adjustable;
FIG. 6 shows a side view of the structure of FIG. 5;
FIG. 7 shows a modification of FIG. 5;
FIG. 8 shows a vertical view partially in section of a hearing aid
wherein the directivity is adjusted by a vane or gate and the
openings face outwardly;
FIGS. 9(a) and 9(b) are drawings useful in explaining the operation
of the embodiment of FIG. 8;
FIG. 10 shows a behind-the-ear hearing aid wherein flexible tubes
extend from the microphone ports outwardly to the hearing aid
housing;
FIG. 11 shows a microphone wherein the size of the cavity is varied
to change the directivity of the microphone; and,
FIG. 12 shows the microphone of FIG. 11 mounted in position in the
hearing aid housing.
DESCRIPTION OF THE INVENTION
It should be understood at the outset that the present invention is
generally applicable to hearing aids of the behind-the-ear type,
in-the-ear type, the eyeglass-mounted type, and other head-worn
types as will become clear hereinafter.
At this point, a brief explanation of certain theoretical
considerations involved herein appears desirable. Note that in the
various Figures, like reference characters refer to like
elements.
It will be understood that the following explanation applies
generally; the various distances, times and directions expressed
are approximate and for purposes of reference; and, are not
intended to be limiting in any way.
FIG. 1 depicts a head-mounted hearing aid 11, which could be of the
behind-the-ear type or the eyeglass-type, see also FIGS. 3, 5 and
10. The microphone capsule 12 of the hearing aid 11, see FIG. 3,
includes two physically spaced or separated sound ports, labeled A
and B which correspond to ports 18 and 20 in FIG. 5. The circular
arc 43 in FIG. 1 represents, at one instant of time, the location
at port A of a bit of information emanating from a sound source No.
1 located in a frontal direction (approximately 0.degree.
incidence) relative to the wearer. At 0.56 inches farther away from
the source No. 1, at the position of port B as indicated by the
dotted circular arc 45, the same bit of information passes 41.4
microseconds later. The microphone 12 recognizes the difference as
a sound signal from the preferred direction and produces a full
output.
In a second case, a bit of information arrives at one instant of
time from a disturbing sound source No. 2 located, in this example,
in a rearward direction (approximately 180.degree. incidence) first
at port B as indicated by circular arc 47 and then approximately
41.4 microseconds later, at port A as indicated by the dotted
circular arc 49. The microphone 12 recognizes this time difference
as an undesired signal and produces minimal output.
Microphone 12 provides the foregoing functions by having a built-in
41.4 microsecond time delay to thereby delay the sound wave
pressure that enters port B by 41.4 microseconds and cause a
subtraction of the sound pressure entering port B from the sound
pressure entering port A.
In the foregoing example of sound coming from source No. 1, the
sound pressure at port B, which is subtracted from the sound
pressure entering at port A. is effective at port A approximately
82.8 microseconds earlier. Thus, the sound pressures are not the
same and these do not cancel each other, therefore an output
results.
In the foregoing example of sound coming from source No. 2, the
sound arrives at port A 41.4 microseconds after it entered port B.
This same sound is delayed 41.4 microseconds by microphone 12 so
that identical pressures are subtracted; and, hence cancel.
In order to permit substantially complete cancellation, the sound
pressures entering the two ports on the microphone capsule should
be equal in magnitude. Thus, the coupling between the apertures in
the hearing aid 11 housing, and the sound ports A and B of the
included microphone capsule 12 should affect both internal sound
paths similarly. The foregoing is most effective if the coupling
paths are resonant well above the frequency range in which the
directivity is desired.
For angles off to the side of the 0.degree. - 180.degree. incidence
line, the time difference in traveling between port A and port B is
less than 41.4 microseconds. This produces less complete
cancellation.
The sound pattern pickup is shown in FIG. 2(a) for one embodiment
of a microphone having an effective port spacing or separation of
0.56 inches, and is the known cardioid polar pattern. The maximum
sensitivity is at 0.degree., one-half maximum sensitivity (-6dB)
occurs at approximately 90.degree. and there is zero sensitivity at
180.degree. .
FIG. 2(b) shows polar pattern characteristics based on port spacing
of 1.08 inches, and FIG. 2(c) shows the polar pattern
characteristics based on a port spacing of 0.29 inches. The latter
two spacings were chosen to provide an approximate 10 dB difference
between the 0.degree. and 180.degree. sensitivity and can be
compared to the sensitivity obtained at 0.56 inches spacing which
provides the cardioid polar characteristic of FIG. 2(a).
Accordingly, a basic feature of the invention is the adjustment of
the directivity of a hearing aid microphone combination to enable
the wearer to adjust the received sound pattern, and the direction
of minimum sensitivity.
In one form, the invention has at least two ports or access
openings where the sound may reach the microphone; and, the
microphone recognizes the difference in time it takes a sound wave
to go between these ports. As will be described, the directivity
may be adjusted by utilizing a structure which permits manipulation
of the effective sound port spacing. Adjustment of the directivity
may also be obtained by adjusting the communication between two
sound ports and the sound inlets. Another modification for
adjusting directivity includes a microphone capsule protruding into
two chambers which have adjustable spaced ports for sound entry; a
compliant support is utilized to support the capsule, and the
support functions as a chamber divider.
Thus, the present invention provides a hearing aid microphone
combination which distinguishes between sounds coming from various
directions, making the overall hearing unit a more useful product,
and enhancing the acceptability of hearing aid devices. More
specifically, by utilizing the inventive hearing aid microphone
combination, it is possible to recognize sound coming from a
preferred direction over the echo and reverberation, and other
interferring sounds, that arrive from other directions. The present
invention provides desired directional characteristics, as well as
minimizing feedback noises and compensating for diffraction or
distortion caused by the wearer's head.
Refer now to FIG. 3, which shows a hearing aid 11 for eye glasses
15 which has a directional microphone capsule 12 located in a
temple piece 17 of the eye glasses. The other known components of
hearing aid 11 including receiver 14 may also be mounted on temple
piece 17, as is well known. As mentioned above, a person wearing
the hearing aid 11 normally wants to face (visually contemplate)
the source of the primary sound, in which he is interested,
indicated by the arrow line 13. In accordance with the present
invention, the hearing aid 11 and microphone capsule 12 provide
improved and adjustable directivity to enable the wearer to
distinguish the desired source of sound.
If the microphone capsule 12 is mounted so that the sound wave has
free access to its sound port regions A and B of FIG. 1, such as by
housing the capsule in an acoustically transparent enclosure or
arranging the hearing aid structure so that the sound ports appear
at the exterior of the structure, the microphone capsule 12 will
exhibit the directional characteristics that are designed into the
capsule.
Refer now to FIGS. 5 and 6. We have found that by mounting the
microphone capsule 12 in a small recess or chamber 21 with
provisions for altering the phase of the sound wave applied to the
sound ports 18 and 20 (corresponding to port A and B of FIG. 1) the
directional characteristics of the hearing aid all can be
adjustably controlled and varied.
Recess or chamber 21 can be conveniently formed in the temple piece
17 or in the behind the ear type of hearing aid, see FIGS. 7 and
10. Recess 21 is enclosed on all sides; one side includes as the
closure element a slidable element with a port, as will become
clear. Microphone capsule 12 is mounted in position intermediate
suitable isolator mounting pads 25, which not only mount the
microphone capsule in position, but also function to effectively
separate the recess 21 into two separate sound cavities 27 and 29
for purposes to be explained.
Microphone capsule 12 is electrically connected as by leads 31, as
is known through an amplifier to the receiver 14 and other known
components of the hearing aid 11 (similarly as indicated in FIG.
10).
A stationary panel or cover 23 positioned over cavity 27 is
suitably attached to temple piece 17; and, a slidably movable panel
or cover 28 is mounted over cavity 29. Panel 23 includes an opening
which functions as a first or front sound inlet 24, and panel 28
includes an opening 26, which serves as a second or rear sound
inlet 26. Panel 28 is movable relative to panel 23 and the purpose
of such movement is control and adjustably vary the separation or
spacing between openings 24 and 26. Relative to a 0.degree.
incidence line, inlet 26 is positioned rearwardly of inlet 24.
The pads 25 mount the microphone capsule 12 so that it seals any
opening between the two cavities 27 and 29. The front port 18 of
the microphone capsule opens or acoustically couples into the front
cavity 27 and the rear port 20 of the microphone capsule opens, or
acoustically couples, into the rear cavity 29. Sound inlet 24
opens, or acoustically couples, to front cavity 27 and sound inlet
26 opens, or acoustically couples to the rear cavity 29.
Under the foregoing structure or conditions, it is the separation
and placement of the sound inlets 24 and 26 coupling respectively
to the cavities 27 and 29 which determine the effectice port
separation; and not, the physical separation of the microphone
capsule ports 18 and 20 themselves. The sound inlets 24 and 26 may
be single large cutouts in the temple piece 17 forming part of the
hearing aid housing, or a plurality of small holes or slits in the
hearing aid housing; and, may include even moderately long tubes
connecting the cavity to the exterior of the hearing aid housing,
as hereinafter described with reference to FIG. 10.
Since the sound openings or inlets 24 and 26 can be variably
adjusted in position with respect to each other, by selectively
controlling the distance between the sound opening 24 and 26, the
directional response characteristics of the hearing aid 11
microphone capsule 12 combination can be adjusted and varied.
Note that for purposes of clarity of illustration, in FIGS. 5 and 6
and in other various Figures, the openings 24 and 26 are shown as
facing upwardly. However, for purposes of minimizing perspiration
and moisture which can enter through the openings 24 and 26 into
recess 21, and for enhancing the draining of any perspiration and
moisture which does get into recess 21, the openings 24 and 26
actually face downwardly. Also, for cosmetic purposes, the openings
24 and 26 may be more suitable faced downwardly.
The microphone ports 18 and 20 are sufficiently large so that the
ports have minimal impedance and do not introduce resonances or
phase shift which would upset the directional characteristics of
the hearing aid. However, high impedance ports can be used as long
as the front cavity/front port, and rear cavity/rear port
combinations are balanced such that the same amplitude changes are
introduced in both places.
As mentioned above, the directivity of the microphone 12 in the
hearing aid 11 is controlled by the separation of inlets 24 and 26
which determine the effective port separation. In general, the
cardioid polar pattern response, indicated in FIG. 2(a), is
obtained for a selected port separation. As the effective port
separation is increased from the selected separation, a response as
indicated by the polar pattern in FIG. 2(b) will be obtained. On
the other hand, as the effective port separation is decreased from
the selected port separation, which provides a cardioid response
and approaches zero, the sensitivity decreases; the response at
180.degree. will no longer be zero; and, the microphone becomes
essentially non-directional as indicated in FIG. 2(c).
Also, it has been found that unwanted amplified sounds, such as for
example, sounds which escape from the acoustical coupling to the
ear including the ear insert 16, (see FIG. 3) or, from the
connections of the sound tube 18, which connects the ear insert to
the hearing aid, may be coupled as an acoustical feedback and
reamplified by the microphone capsule 12 thereby causing whistling
or squealing sounds. Such unwanted sounds appear to come from the
approximate direciton indicated by the arrowed line 33 in FIG.
3.
By adjusting the directivity of the hearing aid microphone
combination, a minimum response can be provided for sound coming
from the approximate direction indicated by the arrowed line 33 to
minimize or eliminate the whistling or squealing sounds.
The aforementioned distortion or shadow effect caused by the human
head of the normal sound patterns effective on a head mounted
hearing aid is depicted in FIG. 4. If, for example, microphone 12X
is mounted at the position indicated in FIGS. 4(a) and 4(b), it
will have a minimal sensitivity to sound coming from the
approximate direction indicated by the arrow 21. Thus, adjustment
of the directivity for the hearing aid 11 microphone capsule 11
combination to provide a minimum response to sound coming from the
direction of the arrowed line 33 also tends to balance the minimum
response to sound caused by the diffraction of the wearer's
head.
Further to the foregoing discussion, since the head alters the
directional response pattern it follows that the exact positioning
of the hearing aid on the wearer's head also affects the
directional response pattern. For example, a hearing aid could be
mounted in the hair on top of the head and preferably near the
forehead to provide a more symmetrical directional pattern than a
hearing mounted behind the ear. In present usage, however, it is
more common to use behind-the-ear, in-the-ear, and eyeglass mounted
hearing aids. In any case, the invention permits the wearer or the
dealer/clinician to adjust the directivity of any of the
aforementioned types of head-mounted hearing aids including the
in-the-hair type to provide the directivity pattern desired by the
individual wearer.
As mentioned hereinbefore, such adjustment will minimize feedback
to minimize the noise and also permit higher acoustical gain which
factor is especially critical with vented ear molds or open ear
fittings; and, will determine the direction of minimum null or
nulls to minimize the reception of undesired sounds from the
direction which a specific user finds most objectionable.
Further, such adjustment permits a single hearing aid to adjust the
sound pattern response nulls such that the most symmetrical pattern
about the medium plane of the hearing aid is obtained. FIG. 2(a)
shows the cardioid response pattern of a directional hearing aid
itself while FIG. 2(d) shows approximately the normal response of
such a hearing aid when it is mounted on a user's head. Note that
the response pattern is rotated approximately 45.degree. and the
null is not sharp.
Referring to FIG. 2(c), for a head-worn hearing aid, two
significant minima occur in the region of approximately
125.degree.-145.degree. and 215.degree.-235.degree.. This hearing
aid when mounted on the head which has a diffraction pattern as
illustrated in FIG. 2(d) combines to provide the sensitivity
pattern shown in FIG. 2(e). Thus, there are a number of variations
in response patterns. However, the invention provides the feature
that whatever the variations in the sound pattern, the wearer or
the dealer/clinician can emperical adjust the directivity of the
hearing aid microphone combination to obtain the optimum response
desired by the wearer.
It should also be understood from the above that while cardioid
response aligned on the 0.degree. axis is indicated as desirable
when the user wants minimum response from a single direction,
variations thereof can be obtained by the proper inlet and port
positioning and orientation.
A second embodiment of the invention is shown in FIG. 7, which
illustrates a portion of a behind the ear type of hearing aid. The
structure of FIG. 7 is generally similar to that of the embodiment
of FIGS. 5 and 6. In FIG. 7, the microphone capsule 12 is mounted
by means of the mounting pads 25 in recess 21. The cover 23A for
the recess 21 extends the full length of the recess and includes a
series of spaced holes or apertures functioning as sound openings,
generally labeled as 30. Plugs or screws or any suitable
obstructions 32 are selectively placed in holes 30 such that only
selected ones of the holes 30 remain open, to thereby adjustably
change the spacing or separation between the sound access opening,
or inlets to the respective cavities 27 and 29, and thence to the
microphone capsule 12 and the sound ports 18 and 20.
FIG. 8 shows another embodiment of the invention which provides
means for controlling the phase of the sound wave arriving at the
sound port regions 18 and 20 of the microphone capsule 12, see also
FIGS. 9(a) and 9(b). The microphone capsule 12 is mounted in a
recess 21 on a suitable mounting pad 25A. Pad 25A is placed as a
bottom and side support for capsule 12; and, a passageway 41
remains open along the length of the capsule to acoustically
connect the left and right hand regions 21A and 21B of recess
21.
Refer now also to FIGS. 9(a) and 9(b) for a brief explanation of
the operation of the structure of FIG. 8. When vane 23 is fully
opened, as shown in FIG. 9(a), the phase of the sound wave arriving
as the microphone capsule 12, indicated by the direction of the
arrowed line 13 represents a distance D1 as shown in FIG. 9(a).
When the vane 43 is closed, the effective phase of the arriving
sound wave is represented by the distance D2 in FIG. 9(b).
Intermediate settings of the vane 43 produces intermediate phase
shifts and intermediate directional characteristics of the hearing
aid microphone combination.
More specifically, a change in the position of vane 43 of FIG. 8
produces a change in directional sensitivity, similarly as does
varying the relative spacing between the sound inlets 24 and 26 of
FIGS. 5 and 6. Refer again to the polar pattern curves of FIG. 2.
FIG. 2(c) for example, indicates the condition when vane 43 is in
the open position shown in FIG. 9(a); that is the microphone
capsule 12 has a sensitivity pattern which is only slightly
directional. As the vane 43 is moved from its open position to its
closed position shown in FIG. 9(b), the directional sensitivity
gradually changes to the pattern shown in FIG. 2(b).
Refer again to FIGS. 5 and 6 as well as to FIG. 4. As mentioned,
the hearing aid 11 microphone capsule 12 combination can be
adjusted to have a null or minimal sensitivity to sound coming from
any desired direction. Thus, by selectively adjusting the effective
port separation (and the vane position of FIG. 8), a minimal
sensitivity can be obtained for sound coming from the direction of
arrowed line 23 in FIG. 4. An advantage of such adjustment, as
mentioned above, is that the unwanted sounds which cause the
aforementioned whistling can be effectively rejected; and, also the
over-all hearing aid can be operated at a higher amplification
level for receiving the desired sounds. An additional advantage is
that the response pattern can be balanced such that the minimal
sensitivity or response to sound coming, say from the direction
indicated by arrowed line 23, can be substantially balanced with
the lowered sensitivity or response to sound coming from the
direction indicated by arrowed line 21 (due to the aforementioned
diffraction provided by the wearer's head), while maintaining
maximum sensitivity to sound coming from a frontal or 0.degree.
incidence direction.
The embodiment of the invention shown in FIG. 10 comprises a
microphone capsule 12A generally similar to microphone capsule 12
of FIG. 5 which is mounted in a chamber 51 of a behind-the-ear type
hearing aid 11. FIG. 10 also shows, as small blocks, usual hearing
aid components including the amplifier, receiver and battery which
are suitably connected as is well known in the art. Hearing aid 11
includes a first or forward sound opening 53 which communicates
through a flexible, extensible tubing 54 directly to port 18A of
microphone 12A. A flexible tubing 59 couples to rear sound port
20A. The free end of tubing 59 forms a second or rear opening 57
facing in an upward direction and turned approximately 90.degree.
relatively to opening 53.
An acoustically transparent cover 64 is mounted to shield the
openings 57 and the outwardly extending tube 59 to minimize wind
noise; and, also to enhance the cosmetic appearance of the hearing
aid.
The forward sound opening 53 is positioned such when the hearing
aid is mounted on the wearer's head the 0.degree. incidence line 13
extends substantially straight ahead of the wearer. Also, the tube
59 is adjustably pivotable about the rear opening 57 to provide
mechanical adjustment of the spacing between the openings 53 and
57.
The embodiment of the invention shown in FIG. 11 comprises a
microphone capsule 12B mounted similarly as shown in FIGS. 5, 6 and
7. In this embodiment, the adjustment of directivity of the hearing
aid microphone housing combination is provided by including an
adjustable phase shifting means in the microphone capsule
itself.
The front port 18 of the microphone capsule 12B is similar to port
18 of FIGS. 5 and 6. The directivity of the hearing aid housing
microphone capsule combination is varied by an adjustable piston or
plate 63 which is mounted as by resilient bellows 68 onto the
interior of the microphone capsule case 62. A set screw 70
protrudes out of the capsule case, and is adjustable to move the
plate 63 into the microphone cavity 60 to vary the size of the
cavity. The adjustment of the acoustical volume of the cavity
controls the phase shift or delay and thus controls the directivity
of the hearing aid microphone combination.
The barometric pressure affects the phase shift produced by an
acoustical impedance and a cavity; accordingly FIG. 11 shows a
hearing aid microphone combination which is essentially independent
of barometric pressure by providing pressure sensitive bellows 63
and 65 which mount a plate 67 which changes the area or size of the
opening of the rear sound port 20B. As the barometric pressure
increases, the bellows contract to tend to restrict the port 20B
and a higher acoustical impedance. Conversely, as the barometric
pressure decreases, the bellows expand to increase the effective
port 20B thereby to reduce the acoustical impedance.
While the invention has been particularly shown and described with
preferred embodiments thereof, it will be understood by those
skilled in the art that various changes in form and details may be
made therein without departing from the spirit and scope of the
invention.
* * * * *