U.S. patent number 3,573,397 [Application Number 04/638,926] was granted by the patent office on 1971-04-06 for acoustic diaphragm and translating device utilizing same.
This patent grant is currently assigned to Tibbetts Industries, Inc.. Invention is credited to Joseph A. Sawyer, George C. Tibbets.
United States Patent |
3,573,397 |
Sawyer , et al. |
April 6, 1971 |
**Please see images for:
( Certificate of Correction ) ** |
ACOUSTIC DIAPHRAGM AND TRANSLATING DEVICE UTILIZING SAME
Abstract
An acoustic diaphragm means for a translating device comprises a
diaphragm portion and a surround therefor, a flexural pivot pin
that extends substantially perpendicular to the diaphragm portion
and attaches the diaphragm portion to the translating device near
one edge of the diaphragm portion, and means for connecting another
portion of the diaphragm portion to the vibratable element of the
translating device, away from the center of pressure of the
diaphragm means. The diaphragm utilized with a translating device,
such as a magnetic type having a vibratable armature, provides a
very high degree of acoustic compliance which enables the armature
to be made thicker, and also permits the diaphragm to be connected
to the armature other than at the midpoint of the diaphragm so that
the diaphragm may be of a size to more fully use the available
area.
Inventors: |
Sawyer; Joseph A. (Camden,
ME), Tibbets; George C. (Camden, ME) |
Assignee: |
Tibbetts Industries, Inc.
(Camden, ME)
|
Family
ID: |
24562014 |
Appl.
No.: |
04/638,926 |
Filed: |
May 16, 1967 |
Current U.S.
Class: |
381/398; 381/423;
181/161; 181/173 |
Current CPC
Class: |
H04R
7/20 (20130101) |
Current International
Class: |
H04R
7/00 (20060101); H04R 7/18 (20060101); H04r
007/20 () |
Field of
Search: |
;179/110--110.6,114 (R)/
;179/115,115 (R)/ ;179/115.5 (ES)/ ;179/138,181
;181/31,32,(Inquired),181 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Blakeslee; Ralph D.
Claims
We claim:
1. An acoustic diaphragm means for a translating device having a
vibratable element, comprising a diaphragm portion and a surround
therefor, means attached to the diaphragm portion away from the
center of pressure thereof for connection to said vibratable
element, and a flexural pivot pin near one edge of the diaphragm
portion and extending substantially perpendicular therefrom for
pivotal support thereof, said diaphragm portion being thereby
restricted to rotary movement about said pivot pin.
2. An acoustic diaphragm means as in claim 1 wherein said
connection means is on the other side of the center of pressure of
the diaphragm portion away from the flexural pivot pin.
3. An acoustic diaphragm means as in claim 1 wherein the diaphragm
portion is elongate, the flexural pivot pin is near one end of the
diaphragm portion, and the connection means is near the other end
of the diaphragm portion.
4. An acoustic transducer comprising a translating device having a
vibratable element, diaphragm means comprising a diaphragm
reinforcement and a surround therefor, means connecting said
diaphragm reinforcement to said vibratable element away from the
center of pressure of the diaphragm reinforcement, and a flexural
pivot pin extending substantially perpendicular from, and pivotally
attaching one edge of, said diaphragm reinforcement to said
translating device, said diaphragm reinforcement being thereby
restricted to rotary movement about said pivot pin.
5. An acoustic transducer as in claim 4 wherein said means
connecting to the vibratable element is on the other side of the
center of pressure of the diaphragm reinforcement away from the
flexural pivot pin.
6. An acoustic transducer as in claim 5 wherein said vibratable
element and said diaphragm reinforcement are each elongate in the
same direction, said flexural pivot pin is near one end of said
diaphragm reinforcement, and said connecting means is near the
other end of the diaphragm reinforcement.
7. An acoustic transducer as in claim 6 wherein said translating
device is electromagnetic and its vibratable element is an armature
having a free end, and said connecting means is attached to the
free end of the armature.
Description
BACKGROUND OF THE INVENTION
The diaphragm of this invention is particularly useful with a
miniaturized translating device. More specifically, it may be
employed in an electroacoustic transducer utilized in hearing aids.
Such transducers, which are bilateral in operation, may be used as
microphones to convert acoustic energy to an electrical signal or
as receivers to convert electrical energy to acoustic energy.
Electroacoustic transducers are being miniaturized for use with
electronic amplifiers of very small size, in hearing aids that may
be small enough to fit well within the pinna of the ear of the user
and to extend into a substantial portion of the external auditory
meatus. As the size of the transducer is reduced, new structures
must be created to obtain optimum performance in reduced size.
One element of particular concern is the diaphragm of the
electroacoustic transducer. Such diaphragm must permit the
associated transducer to be fabricated easily in very small size,
and it must utilize the shape and size of such transducer to best
advantage. For example, the diaphragm must be able to be attached
to the freely vibrating portion of the active element of the
transducer at an optimum position near the point of maximum
excursion of the vibrating portion, with no detrimental effect on
the size or performance of the transducer.
The prior art has partially achieved such features in various ways.
Thus in the series magnetic circuit configuration of translating
device disclosed in the copending application of George C.
Tibbetts, Ser. No. 168,183 filed Jan. 23, 1962, and in the
diaphragm construction thereof disclosed more fully in U.S. Pat.
No. 3,166,148 of George C. Tibbetts, the diaphragm means may
comprise a laminate sheet of plastic and metal, with part of the
sheet defining a diaphragm portion, another part defining a
compliant surround etched free of metal, and a third part defining
a support area exterior of the surround. The support area is
secured to a frame attached to the housing of the translating
device, and the center of pressure of the diaphragm portion is
connected by a drive pin to a portion of the armature near its free
end. The center of acoustic pressure must coincide with the central
drive point and thus it is not possible to have the diaphragm
portion utilize the entire geometrical area available. As can be
seen in FIG. 5 of either the patent or the copending application,
the diaphragm is square (symmetrical about the drive point) and
located near one end of the rectangular frame, with a portion of
the frame occupying an area that could otherwise be utilized by the
diaphragm portion if the center of acoustic pressure did not have
to coincide with the drive point. By pivoting or hinging one end of
the diaphragm and connecting the drive pin to the opposite end
thereof as in the present invention, this restriction is
eliminated.
SUMMARY OF THE INVENTION
We have devised an improved diaphragm for use in electroacoustic
translating devices. While the invention will be described in
connection with a magnetic electromechanical transducer utilized in
miniaturized hearing aids, the diaphragm of this invention is not
of such limited application and may be equally useful in
electroacoustic translating devices of other types and for other
applications.
Accordingly we provide an acoustic diaphragm pivotally attached by
a substantially perpendicular flexural pivot pin to a support
member near one edge of the diaphragm, with a drive pin connected
near the opposite edge of the diaphragm on the other side of and
away from the center of pressure of the diaphragm. The drive pin
leads to and is connected to the vibratable element of a
translating device at one edge portion thereof, with the vibratable
element extending substantially parallel to the diaphragm from the
drive pin toward the pivotal attachment.
Such diaphragm permits the associated translating elements and
overall electroacoustic translating device to be fabricated more
easily and in very small sizes, including fabrication in elongate
shapes of very small cross section. The diaphragm is useful with
translating devices that utilize to best advantage the shape and
size constraints on devices applicable in practice. The pivoted
diaphragm eliminates a spurious mode of vibration, and enables
greater utilization of the available geometrical area since the
center of acoustic pressure does not have to coincide with the
drive point. Such diaphragm when utilized with an end-driven
translating device provides high acoustic compliance and, in
receiver embodiments, an acoustic volume displacement equal to or
better than that obtained with a conventional translating device
with a diaphragm driven at its geometric center. Due to the nature
of the present system, its resistance to damage by shock is better
than that of the more conventional type of electroacoustic
translating devices, and its accelerometer sensitivity is less.
These and further objects will become apparent from the
accompanying specification and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side sectional view of a general representation of the
diaphragm of this invention;
FIG. 2 is another side sectional view similar to FIG. 1 with a
drive pin in a different position;
FIG. 3 is an exploded perspective view of a magnetic-type
electroacoustic transducer utilizing a diaphragm according to the
invention; and
FIG. 4 is a side view of a general representation of prior
diaphragms showing a mode of vibration that may be undesirable when
not constrained.
SPECIFIC DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the drawings, FIG. 1 shows a general representation of
a diaphragm means 1 comprising a diaphragm portion or reinforcement
2 and a flexible surround 3 connected to the periphery of the
diaphragm reinforcement and to a supporting means shown generally
at 4. Unlike diaphragms of the prior art, diaphragm portion 2 is
pivotally attached near one edge to a supporting means 5 by any
suitable means such as a hinge, but preferably is connected by a
flexural pivot 6 to means 5. A drive pin or connecting pin 7 is
attached to the diaphragm reinforcement on the other side of and
away from the center of pressure of the diaphragm, which may be
near one edge of the diaphragm reinforcement 2 as shown. In FIG. 2
the connecting pin is not as near to the edge of the diaphragm
reinforcement. Connecting pin 7 leads to and is connected to the
vibratable element 8 of a translating device which operates in
flexure or torsion, preferably at or near one edge such as the end
thereof. For best utilization of available space, the vibratable
element extends substantially parallel to the diaphragm from the
connecting pin 7 toward the pivotal attachment 6, and may be
attached to a portion of supporting means 5 such as in the vicinity
of flexural pivot 6.
Pivoting the diaphragm near one edge to a supporting means enables
the diaphragm reinforcement to function substantially as a lever.
In a microphone embodiment, sound waves drive the diaphragm portion
over its entire area, and can be treated as a force b applied at
the center of pressure of the diaphragm reinforcement at a distance
a from the flexural pivot 6. Driving force Y can be taken off the
diaphragm reinforcement at any desired distance x from the pivot 6,
with the diaphragm reinforcement functioning substantially as a
lever. The driving force available and the amplitude of movement
vary linearly with change of distance from the pivot point. As the
distance x increases the amplitude of movement increases and the
driving force y decreases.
However, referring to FIG. 2, the stiffness s of the vibratable
element 8 of the translating device is inversely proportional to
the cube of t, where t is the distance from the point of attachment
of element 8 at supporting means 5 along element 8 to connecting
pin 7. As the drive point is shifted away from the point of
attachment, the stiffness decreases at an ever-increasing nonlinear
rate, much faster than the linear decrease of driving force y. At
some point a net gain in acoustic compliance first appears. The
greatest-gain results when the vibratable element 8 is driven at
its extreme end. The above discussion is merely a generalized
qualitative description of the effects of the construction shown in
FIGS. 1 and 2, with losses ignored for purposes of simplicity.
If a conventional acoustic transducer of magnetic type with drive
at the midpoint of the armature (at a distance a from the fixed end
of the armature) is compared to the present end-driven armature
(with drive at a distance 2a from the fixed end of the armature),
the mechanical compliance at the drive point of the end-driven
armature would be approximately eight times the compliance at the
drive point of the midpoint-driven armature, for a given thickness
of the armature, and in combination with the pivoted diaphragm
would provide an acoustic compliance approximately twice that of
the conventional configuration.
That acoustic compliance can be made equal to the acoustic
compliance of the assumed conventional case by increasing the
thickness of the armature by the cube root of 2, and therefore the
diaphragm of this invention allows an armature thicker by this
factor when designing for a specified acoustical compliance of the
combination. In a magnetic transducer, the thicker armature
provides increased flux-carrying capability. The end-driven
configuration does not require an aperture through the armature for
the drive pin, and thus the flux-carrying capability of the
armature is also increased for that reason. The thicker armature
has an increased stiffness, and a deflection that would be reduced
except that the change of location of forces compensates for the
otherwise reduced deflection and provides an amplitude of
deflection at the end of the end-driven armature slightly more than
twice that of the deflection at the midpoint of the conventional
case. The pivoted diaphragm divides out the factor 2, leaving an
estimate that the end-driven armature configuration produces, in a
receiver embodiment, a slightly increased volume displacement over
that provided by the conventional configuration. Because of the
many variables indicated above, it is difficult to estimate the
exact amount of increase of volume displacement.
The end-driven configuration has a clear advantage in its increased
resistance to damage by mechanical shock, because the armature can
be thicker as noted above. Furthermore, as stated above the
end-driven configuration does not need an open aperture in the
armature which acts as a stress concentrator, and the armature
without an an aperture is thus more resistant to mechanical
shock.
Because of its greater thickness, the mass of the armature in the
end-driven configuration is greater than that in the
midpoint-driven configuration. However, the increased mechanical
stiffness more than compensates for this added mass, and therefore
the accelerometer sensitivity will be less than that of the
conventional configuration.
In the embodiment shown in FIG. 3, a diaphragm according to the
invention may be utilized with a magnetic-type transducer such as
that disclosed in copending application Ser. No. 638,878 of George
C. Tibbetts et al. filed of even date. Preferably a diaphragm means
of the type disclosed in U.S. Pat. 3,166,148 of George C. Tibbetts
is employed, and may comprise a diaphragm portion 9, a diaphragm
surround 10, and a self-frame 11 having a peripheral rim 12. The
diaphragm portion 9 may have flats 13 and 14, and between the flats
the diaphragm portion may be formed so as to increase greatly the
flexural stiffness of the diaphragm portion. For example the form
may correspond to a continuous trough generated by a portion of a
sphere the projection of whose center follows a contour between
flats 13 and 14. A frame 15 has a peripheral rim 16, an aperture
defined by edge 17, and a formed boundary 18 adjacent the aperture.
The diaphragm peripheral rim 12 fits within rim 16 and boundary 18
of the frame and is bonded and sealed together therewith by
adhesive. Flexural pivot 19 connected to the magnetic translating
device 24 extends up through aperture 20 in flat 13 and is attached
to the diaphragm portion by an adhesive mass, not shown for the
sake of clarity. Connecting pin 21 connected to the end 27 of the
armature 26 extends up through aperture 22 in flat 13 and is
similarly attached thereto by an adhesive mass not shown. The
diaphragm is protected and a space above the diaphragm is provided
by a cover 23 which is located by rim 16 of the frame 15. After
adhesive is applied about the junction of the rim 16 with the
sleeve 25 of the magnetic translating device, the cover is fitted
in place, and the adhesive bonds the cover to the frame and to the
sleeve and serves also to seal the frame to the sleeve. The frame
15 and cover 23 may be fabricated from magnetic material to provide
magnetic shielding against stray flux traversing the apertures in
the sleeve containing the flexural pivot 19 and connecting pin
21.
The remainder of the structure shown in FIG. 3 comprises the
magnetic transducer 24 disclosed in said copending application of
George C. Tibbetts et al., and includes a sleeve 25 of magnetic
material, an armature 26 having an end 27 to which is attached
connecting pin 21, a coil 28, a magnet stack 29, a U-shaped closure
member 30 at one end of the sleeve, a terminal board 31 having
terminals 32 thereon, and other components more fully disclosed in
said copending application. The electroacoustic transducer of FIG.
3 may function as either a microphone or a receiver. In operation
as a microphone, sound pressure may have access to the space
between the diaphragm and cover by an aperture through the cover or
by passage from the end of the transducer through appropriate
conduits and chambers to said space. The diaphragm will be actuated
by such sound pressure and will pivot about the end due to
attachment to flexural pivot 19. The other end of the diaphragm
will move connecting pin 21 which in turn actuates the armature 26.
The armature can be thicker than in conventional transducers as
noted above, and will have flux induced along its length by
movement in the working gap of magnet stack 29,7 which flux will
induce in E.M.F. in coil 28 led to the output terminals 32.
In prior structures such as the translating device shown in FIG. 2
of U.S. Pat. No. 3,154,172 of George C. Tibbetts, the connecting
pin is attached to a portion of the armature inwardly of the end
and extends up in a space between the coil and the magnet stack.
That space is in addition to the space between the magnet stack and
the end of the casing, necessary to prevent shorting the magnet
stack. The connecting pin could not be of yoke form as in prior
structure such as shown in FIG. 5 of U.S. Pat. No. 2,994,016 of
Raymond W. Tibbetts et al., but due to the nature of the assembly
had to be a straight pin extending through a hole in the armature.
Such hole, acting as a stress concentrator, weakens the armature
even though the armature is widened at that point. With the present
invention the connecting pin may be attached to the end of the
armature at the point of greatest compliance, with no hole through
the armature, and no extra space is provided for the pin since it
utilizes the space necessary to prevent shorting the magnet stack.
Thus the coil and magnet stack can be compacted together.
Furthermore, in manufacture this may be made a subassembly before
insertion into the sleeve, simplifying the overall assembly
process.
FIG. 4 shows a generalized form of the prior art diaphragm having a
central drive pin. A flexible surround (not shown) substantially
prevents translation of the diaphragm reinforcement 33 to the right
or left of the figure, but provides very little restraint against
rotation about the point of attachment to the connecting pin 34, as
shown in dotted lines. During such rotation the connecting pin
flexes, as also shown in dotted lines. In FIG. 4 the rotation is
shown relative to an undeflected armature, illustrating that in
prior art devices a hitherto unrecognized mode of vibration, i.e.
an extra degree of freedom, exists in general. A mode of this type
can absorb or reflect mechanical energy, and may and commonly does
cause frequency response distortion within the passband of the
transducer. The rotation of the diaphragm reinforcement is not
undesirable in itself; in this invention the diaphragm operates in
rotation about the pivotal point. What may be undesirable is the
situation in which the diaphragm is free to rotate irrespective of
the motion of the armature. In this invention, the rotation of the
diaphragm is in one-to-one correspondence with the vertical
deflection of the end of the armature, insofar as the diaphragm can
be considered to be a rigid body. It follows that the extra degree
of freedom has been substantially removed.
Many modifications will be apparent to the artisan, in choice of
materials or shape and location of elements, and the invention is
applicable to circular, oval, elliptical or other shapes of
diaphragms as well as to the square, rectangular, and racetrack
shapes discussed above. For example a flat hinge in the plane of
the diaphragm may be utilized instead of the flexural pivot pin,
with the hinge taking the place of or comprising part of the
surround. If so-called mechanical advantage is desired, the pivot
may be near the edge portion neighboring the connecting pin, with
the connecting pin spaced between the center of pressure of the
diaphragm and the pivotal point, but still connected to the end of
the translating element. Receiver embodiments may utilize
configurations different from those used in corresponding
microphone embodiments.
The invention is to be limited only by the scope of the following
claims.
* * * * *