U.S. patent number 3,573,396 [Application Number 04/688,296] was granted by the patent office on 1971-04-06 for loudspeaker having improved diaphragm.
This patent grant is currently assigned to Electronic Research Associates, Inc.. Invention is credited to Herbert Schoengold.
United States Patent |
3,573,396 |
Schoengold |
April 6, 1971 |
LOUDSPEAKER HAVING IMPROVED DIAPHRAGM
Abstract
A loudspeaker assembly of a thin, compact, lightweight
construction having a diaphragm which preferably is formed of
cellular plastic material and provided with an integral marginal
gasket. The diaphragm is mounted on a frame which is preferably
formed of a solid body of the same or acoustically similar plastic
material. The diaphragm has a concavo-convex form modified with
acoustical materials and is capable of faithfully reproducing low
frequency, midrange, and high frequency vibrations. The diaphragm
is actuated by a voice coil mounted at the rear of the convex zone
of the diaphragm, whereby the diaphragm and the magnetic assembly
for actuating the same are constructed and arranged so as to
provide an assembly which is not only relatively thin but may also
present a labyrinth type of dust shield for the diaphragm actuating
means. The frame further incorporates built-in centering and
spacing tooling which is removed following manufacture.
Inventors: |
Schoengold; Herbert (Mount
Vernon, NY) |
Assignee: |
Electronic Research Associates,
Inc. (Cedar Grove, NJ)
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Family
ID: |
27561253 |
Appl.
No.: |
04/688,296 |
Filed: |
November 17, 1967 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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342827 |
Feb 5, 1964 |
3351719 |
|
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648089 |
Jun 22, 1967 |
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Current U.S.
Class: |
381/433; 181/165;
381/420 |
Current CPC
Class: |
H04R
7/12 (20130101); H04R 9/063 (20130101); H04R
7/04 (20130101); H04R 7/20 (20130101); H04R
9/045 (20130101) |
Current International
Class: |
H04R
9/00 (20060101); H04R 7/00 (20060101); H04R
7/12 (20060101); H04R 9/04 (20060101); H04R
7/04 (20060101); H04R 7/20 (20060101); H04R
9/06 (20060101); H04r 007/02 (); H04r 009/06 () |
Field of
Search: |
;179/115.5,115.5 (ES)/
;179/179,180,181 ;181/31.1,31 (A)/ ;181/31 (FD)/ ;181/32 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Claffy; Kathleen H.
Assistant Examiner: Kundert; Thomas L
Parent Case Text
RELATED APPLICATIONS
This application is a continuation in part of applicant's copending
application Ser. No. 342,827 filed Feb. 5, 1964 and now U.S. Pat.
No. 3,351,719 and Ser. No. 643,089 filed Jun. 22, 1967.
Claims
I claim:
1. A relatively thin flat loudspeaker assembly comprising a frame,
a diaphragm having a central flat zone surrounded by an inclined
connecting surface extending from said central zone to an outer
sound-reproducing zone of the diaphragm which is inclined
oppositely to said connecting surface, compliance grooves in the
diaphragm between said outer zone and marginal edges of the
diaphragm, the marginal edges of the diaphragm being connected to
said frame and lying in substantially the same plane as the central
zone of the diaphragm, a voice coil connected to the central flat
zone of the diaphragm near the midportion thereof, and a magnetic
assembly supported by said frame and located adjacent said voice
coil for actuating said diaphragm.
2. Sound-reproducing equipment as defined in claim 1 wherein the
central flat zone of the diaphragm has an annular reinforcing rib
extending rearwardly from the marginal portions thereof into a
position surrounding the magnetic assembly and serving as a dust
guard establishing a labyrinth passage between said rib and the
magnetic assembly.
3. Sound-reproducing equipment as defined in claim 1 wherein the
frame and diaphragm are substantially rectangular in shape and said
compliance grooves extend parallel to the longitudinal edges only
of said diaphragm.
4. Sound-reproducing equipment as defined by claim 1 wherein the
diaphragm is formed with compliance means adjacent the marginal
edges thereof, said compliance means being provided with slots
therein extending inward from edges of the diaphragm toward said
voice coil.
5. Sound-reproducing equipment as defined in claim 1 wherein said
frame and diaphragm are generally rectangular in shape, compliance
means in the form of corrugations are formed in said diaphragm
adjacent the marginal edges of the diaphragm, and slots are formed
in said corrugations and extend diagonally inward from edges of the
diaphragm near the corners of said diaphragm.
6. Sound-reproducing equipment as defined in claim 1 wherein said
diaphragm is formed of stiff, cellular plastic material and the
marginal edges of the diaphragm are provided with an integral
compressible gasket consisting of a thickened marginal rim of said
cellular plastic material.
7. Sound-reproducing equipment as defined in claim 1 comprising a
diaphragm formed of cellular plastic material, a frame formed of a
solid body of plastic material, the marginal edges of said
diaphragm being supported by said frame, and means carried by said
frame for actuating said diaphragm.
8. Sound-reproducing equipment as defined in claim 7 wherein the
diaphragm and frame are formed of plastic material having
essentially the same composition.
9. Sound-reproducing equipment as defined in claim 7 wherein said
diaphragm has a central portion presenting a convex surface lying
in substantially the same plane as the marginal edges of the
diaphragm and surrounded by a portion of said diaphragm presenting
a concave surface, a voice coil mounted on a voice coil form
connected to said central portion of the diaphragm and projecting
from the concave side thereof, a magnetic assembly surrounding said
voice coil, said frame having a ring in which said magnetic
assembly is mounted and arms extending from said ring to said
frame.
10. A sound-reproducing device as defined in claim 1 wherein said
diaphragm is formed of cellular plastic material and said frame is
formed of a solid body of plastic material.
11. A sound-reproducing device as defined in claim 1 wherein the
central portion of the diaphragm is provided with an insert secured
about its edges to the surrounding portions of the diaphragm by
compliant damping material.
12. A sound-reproducing device as defined in claim 1 wherein the
central portion of the diaphragm is at least partially decoupled
from the remaining portions of the diaphragm.
13. A sound-reproducing device as defined in claim 3 wherein the
diaphragm is provided with slots extending diagonally inward from
the corners thereof and the portions of the diaphragm at opposite
sides of said slots are secured to the frame by yieldable
means.
14. A sound-reproducing device as defined in claim 1 wherein the
frame is provided with removable positioning elements for assuring
accurate location of the diaphragm with respect to the frame.
Description
FIELD OF THE INVENTION
The invention relates to loudspeaker assemblies of novel
construction which are thin, light in weight, and acoustically
designed to faithfully reproduce a wide range of sound
vibrations.
DESCRIPTION OF THE PRIOR ART
Many types of loudspeaker assemblies have been heretofore designed
but most constructions in current use embody conical diaphragms
with a voice coil and magnetic assembly projecting rearwardly from
the apex of the diaphragm, with the result that the assembly does
not lend itself to the production of a thin flat assembly. Also,
the conical designs because of opposing sound vectors provides an
effective radiating area which is substantially smaller than the
physical aperture. On the other hand those loudspeakers heretofore
available which are provided with a relatively flat diaphragm have
of necessity been of relatively large area and weight in order to
permit even a limited reproduction of a broad band of
frequencies.
A further problem presented by loudspeakers used in exposed area,
or out of doors, and in automobile radios has developed by reason
of the accumulation of dust and dirt in the air gap in which the
voice coil is located whereby electrical and mechanical
interference or damping of the voice coil develops so as to impair
the operations of the loudspeaker.
Further, in the manufacture of loudspeakers accurate spacing tools
and jigs are required to properly space diaphragms and voice coils
in the structure, which adds to the cost and manufacturing
difficulty.
SUMMARY OF THE INVENTION
In accordance with the present invention the foregoing objections
and limitations of the prior art are reduced or eliminated by
providing a loudspeaker assembly embodying a diaphragm and
supporting frame of novel design and construction wherein the
diaphragm is of a concavo-convex form modified by plastic
acoustical materials and designed in such a fashion as to
materially reduce the overall thickness of the assembly. The voice
coil and magnetic assembly are then located at the rear of the
convex zone of the diaphragm so as to further limit the thickness
of the loudspeaker. Moreover, by forming the diaphragm of cellular
plastic material it is possible to mold a marginal compressible
gasket integral with the diaphragm for contact with the frame of
the speaker so as to prevent or reduce any distortion of the frame
or diaphragm in mounting the diaphragm on the frame. Such an
integral gasket also eliminates the need for separate gasket to
seal the speaker to its mounting.
The diaphragm also is formed with a ring or dust guard positioned
to surround the magnetic elements and voice coil in a manner to
present a labyrinth shield about these elements which reduces the
danger of dust accumulation on the voice coil and in the air gap in
which it is movable.
A further feature of the applicant's invention resides in the
discovery of the fact that improved and more faithful reproduction
of low frequency vibrations can be attained by forming radially
extending slots or grooves in compliance zones adjacent the
peripheral portions of the diaphragm and particularly at the
corners of a rectangular diaphragm, and that such improvement is
enhanced by filling such slots or grooves with a permanently
compliant or elastic material.
An additional feature is the incorporation of spacing elements
which are integral in the molding of the frame and which are
removed after manufacture.
A further feature is a novel floating center element attached to
the diaphragm which serves to eliminate resonant and antiresonant
conditions at higher frequencies and thus provide a smooth response
curve.
A further feature is the inclusion of tabs formed from compliant
acoustical materials, located at the corners of the diaphragm and
attached to the corners of the frame. These tiedown tabs serve to
prevent low frequency breakup and to remove resonant and
antiresonant excursions at the lower frequencies.
BRIEF DESCRIPTION OF THE DRAWING
FIG. - is a perspective illustrating a preferred form of
sound-reproducing equipment embodying the present invention as seen
from the front thereof;
FIG. 2 is a perspective showing the rear of the device shown in
FIG. 1;
FIG. 3 is a vertical sectional view through the loudspeaker
assembly shown in FIGS. 1 and 2 taken on the line 3-3 of FIG.
4;
FIG. 4 is a plan view of the diaphragm embodied in the assembly of
FIGS. 1 and 2;
FIG. 5 is a plan view of the frame of the loudspeaker in the
assembly of FIGS. 1 and 2; and
FIG. 6 is a transverse sectional view through one longitudinal edge
of the diaphragm and frames taken on the line 6-6 of FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In that form of the invention chosen for purposes of illustration
in the FIGS. of the drawing, the diaphragm is indicated at 2 and is
mounted on a frame 4 which is illustrated as being of a rectangular
shape, although it may of course, be square, circular, bent out of
the plane of the drawing, or of any other configuration. However,
as shown, and in order to provide an assembly which is unusually
thin and compact, the diaphragm 2 is preferably formed with a
central zone or area 6 which is surrounded by a rearwardly and
outwardly inclined surface 8 so as to render the central portion of
the diaphragm generally convex. The outer portion or zone 10 of the
diaphragm is inclined forwardly and outwardly from the inclined
portion 8 of the diaphragm terminating in an edge 12 which is
preferably located in substantially the same transverse plane as
the outer face 14 of the convex central zone 6 of the diaphragm.
The diaphragm thus has a concavo-convex configuration.
The portion of the diaphragm surrounding the edge 12 thereof may be
relatively thin and formed with corrugations or grooves as shown at
16 to provide compliance zones about the periphery of the diaphragm
proper to afford the desired freedom of movement of the diaphragm
during operation. It has further been discovered that greater
compliance and substantially improved low frequency response is
attainable by providing diagonally extending slots or grooves 18 in
the corrugations or peripheral compliance zones 16 of the
diaphragm. Such grooves are of particular advantage when the
diaphragm is rectangular in shape as illustrated and the slots 18
extend inward from the corners of the diaphragm through the
compliance zones to the outer edge 12 of the diaphragm 2.
It has also been found in many instances that it is preferable to
provide damping means in the form of compliance grooves or
corrugations 16 having yieldable damping material 17, such as a
silicone rubber composition therein. The grooves or corrugations 16
preferably extend along two opposite sides only of the diaphragm as
shown in FIG. 4; whereas the two remaining sides of a rectangular
diaphragm have no such damping or compliance means. Thus, as shown,
when the diaphragm is of greater length than width, the longer
sides may be provided with marginal strips or edge portions formed
with the compliance means in the form of corrugations 16 having a
damping means or composition therein as shown in FIG. 6. The
shorter side or opposite ends of the diaphragm may then be flat and
extend outward as shown in FIG. 3 into positions wherein the
thickened gasket edge 22 of the diaphragm bears against the
supporting surface 20 at the ends of the frame 4. When the
diaphragm is thus formed the slotted corners thereof at opposite
sides of the diagonal slots 18 are preferably secured to the frame
by yieldable means such as compliant tabs or material indicated at
19. The construction thus provided serves to reduce or prevent low
frequency breakup and to eliminate unwanted resonant and
antiresonant excursions of the diaphragm at low frequencies. As a
result the frequency response is smoothed out and more faithful
sound reproduction is attained.
The diaphragm 2 may be formed of any suitable stiff, light weight
vibratory material but is preferably formed of cellular material
such as an expanded plastic composition of the type which may be
produced by molding and expanding porous beads of polystyrene or
the like. In molding or forming the diaphragm the portion which
constitutes the peripheral compliance zones 16 is relatively thin
as compared to the concavo-convex area of the diaphragm. The outer
edge of the peripheral compliance zone 16 of the diaphragm may be
cemented or otherwise secured to the forwardly facing surface 20
which extends inwardly from the outer marginal sides of the frame 4
of the assembly. Furthermore, in the preferred embodiment of the
invention, the outer marginal portion of the diaphragm 2 is
thickened as shown at 21 in FIG. 7 to provide an integral gasket
between the diaphragm and the frame. This gasket is compressible so
as to be reduced in thickness as shown by dotted line 21A of FIG. 7
upon the application of bolts or other securing means 24 at the
corners or elsewhere. In this way it is possible to establish a
firm air seal between the speaker and mounting structure without
introducing strains or physical distortion in the speaker. As a
result optimum acoustical performance is obtained without the need
of external sealing or gasketing.
Another feature of the diaphragm is the inclusion of a ring
structure of the same material, molded integral with the diaphragm.
This ring fits around the magnet structure when assembled in the
frame and serves to provide a long and sinuous path for dust or
dirt to travel, thus protecting the structure from failure due to
dust accumulating in the magnetic gap.
The central convex zone 6 of the diaphragm 2 is provided with a
voice coil form 26 which projects rearwardly from the zone 6 so as
to be located behind the convex zone. The voice coil form 26 is
cemented or otherwise secured to the central portion of the zone 6
and for ease in assembly the diaphragm may be formed or molded with
a central opening 28 therein providing for insertion and a close
fit between the voice coil form and the inner surface of the
opening 28. Cement, glue or other means 30 may be employed to
secure the outer end of the voice coil form 26 to the inner
surfaces of the central opening 28 so as to fixedly bond and
position the voice coil form in place. The voice coil 32 is wound
upon the voice coil form 26 and by reason of the fact that the
central zone 6 of the diaphragm is convex, the voice coil 32 is
actually positioned in a plane which is substantially parallel to
the plane of the inner surface of the outer portion or zone 10 of
the diaphragm. Thus, the total depth of the diaphragm and its voice
coil assembly is substantially no greater than the total depth of
the concavo-convex diaphragm itself.
In order to complete the diaphragm and provide the desired piston
surface for most effective propagation of sound waves thereby, the
outer end of the voice coil form 26 is closed by an insert 34. The
insert preferably is of the same thickness, composition and density
as the surrounding convex zone 6 of the diaphragm and is secured to
the inner surface of the voice coil form in the plane of the outer
surface of the zone 6 by means of acoustical material such as a
silicone rubber composition which serves both as an adhesive and to
independently suspend and at least partially decouple the insert 34
from the surrounding portions of the diaphragm. It has been found
that the damping effect of a properly chosen acoustical material
serves to cause acoustical vibrations which would normally traverse
the center of the diaphragm to be damped out thus reducing
distortion and improving the frequency response.
The frame 4 of the assembly illustrated is formed of a material
having compatible physical and acoustical properties serving to
limit the disparity in acoustical properties at the junction or
joint between the diaphragm and frame. For this purpose the frame
may be formed of an injection molded plastic material, such as
unexpanded polystyrene, for example, having physical and acoustical
properties which are the same or similar to those of the cellular
or expanded polystyrene diaphragm itself.
As shown most clearly in FIG. 3 of the drawings, the frame 4 has
relatively narrow sides 40 and 42 and similar relatively narrow
ends 44 and 46 defining a rectangular outer frame with the
forwardly facing diaphragm-supporting seat or surface 22 which
projects inwardly from an outer marginal diaphragm-positioning rim
48. The sides and ends of the frame 4 are stiffened and maintained
in a common plane by means of the upward and downward extension of
the rim 48 with respect to the diaphragm-supporting surface 22 and
by means of a further downwardly and inwardly extending reinforcing
rib 50 which extends parallel to the downwardly projecting portion
48A of the diaphragm-positioning rim 48.
The magnetic assembly 52 which serves to actuate the diaphragm 2 of
the loudspeaker is supported by the web 54 consisting of arms 56
which extend inwardly from the marginal frame at suitable points
and preferably extend inward from the corners of the frame to a
magnetic assembly supporting ring 58. The ring 58 is preferably
formed integral with the arms 56 and marginal frame numbers 40, 42,
44 and 46 as a portion of a molded unitary body.
The ring 58 presents a lower inwardly projecting flange 60 and an
outer upwardly extending annular rim 62. The magnetic assembly
which cooperates with the voice coil 32 to actuate the diaphragm
preferably embodies a ring-shaped permanent magnet 64 which fits
closely within the annular rim 62 and rests upon the inwardly
projecting flange 60 of the ring 58 of the frame number. An annular
bottom plate 66 formed of ferromagnetic material fits with the
flange 60 of ring 58 and has a central pole piece 68 mounted
thereon and projecting upward within the voice coil form 26. A top
plate 70 formed of ferromagnetic material is located above the
permanent magnet 64 and projects inwardly therefrom to cooperate
with the pole piece 68 to present an air gap 72 of limited cross
section within which the voice coil 32 on the voice coil form 26 is
freely movable.
As shown in FIG. 3 of the drawings, the upper extremity 74 of the
annular rim 62 of the ring 58 is preferably reduced in thickness
and is turned inwardly over the upper face of the permanent magnet
64 and toward the outer edge of the top plate 70 to hold the
magnetic assembly securely in place within the ring 58 of the
frame. Such inward folding or spinning of the extremity 74 can be
effected by means of a heated tool or the application of a volatile
solvent or the like thereto so as to establish a fixed and
permanent mounting of the magnetic assembly in the ring 58 of the
frame and in a predetermined and immovable relation with respect to
the voice coil 32 carried by the diaphragm 2.
In order to supply diaphragm actuating current to the voice coil 32
the diaphragm 2 is preferably provided with grooves 80 in which the
electrical leads 82 connected to the voice coil are located. The
leads 82 are preferably embedded in a compliant plastic material
which substantially fills the grooves 80 and serves to hold the
leads 82 in place preventing vibration or displacement thereof. The
outer ends of the leads 82 are connected to a terminal block 84
mounted in or on the side member 42 of the frame 2 for connection
with a suitable source of energizing current. As shown the terminal
block 84 is preferably received and retained in place on the frame
by means of a locating pin 86 and a positioning web 88 so as to
enable the terminal block to be snapped into place assuring proper
location and retention thereof.
When the various elements of the assembly are constructed as herein
described, the diaphragm 2 may be placed in position with integral
marginal gasket 21 of the diaphragm resting upon the inwardly
facing supporting surfaces 22 of the side and end members 40, 42,
44 and 46 of the frame 4. The compressible gasket 21 of the
diaphragm is preferably cemented in place on the surface 22 of the
diaphragm of the frame and the frame and gasket are bolted, clamped
or otherwise secured together by securing means. Such securing
means may extend through the mounting holes 24 passing through the
gasket 21. In this way gasket 21 is compressed and the diaphragm
and frame securely fastened together with the voice coil 32 carried
by the diaphragm accurately positioned within the air gap 72 of the
magnetic assembly. Moreover, in order to assure the most accurate
and uniform assembly of the diaphragm and frame, the frame 4, as
initially molded, is provided with spacing elements 73 which serve
to assure proper registration and spacing of the frame and
diaphragm until the cement between the gasket and surface 20 has
hardened. The spacing elements 73 can then be broken off or removed
to permit the diaphragm to vibrate properly.
An important feature of the present invention resides in the
provision of means to shield the voice coil, air gap and associated
elements from the adverse effects of dust accumulations which might
impair the operation of the loudspeaker, the central convex zone 6
of the diaphragm is provided with a rearwardly extending annular
ring 90 which preferably is formed integral with the diaphragm and
surrounds the top plate 70 or other portions of the magnetic
assembly so as to cooperate with the ring 58 of the frame to
present a labyrinth barrier between the voice coil and air gap of
the diaphragm actuating means and the exterior of the assembly. In
this way the entry of dust and dirt into contact with the
relatively movable elements of the diaphragm actuating means is
precluded and the equipment may be used in automobiles and
elsewhere under adverse conditions which would tend to impair or
interfere with the most effective and faithful operation and sound
reproduction by the loudspeaker. The annular ring 90 preferably is
located in alignment with the outer edge of the central zone 6 of
the diaphragm 2 so as to cooperate therewith in establishing a
relatively high frequency vibratory area in the diaphragm. At the
same time the diaphragm is provided with yieldable damping material
on the inner surface thereof and about the annular ring 90, as
shown at 92 and 94, whereby a smoother frequency response is
attained and resonant and antiresonant responses are reduced.
The sound-reproducing equipment produced in accordance with the
present invention and described above is unique in that the overall
thickness of the assembly may be substantially less than 1 inch,
whereas the tone qualities, volume and range of frequencies which
can be faithfully reproduced is substantially equal to that
attainable heretofore by the use of much larger, heavier and far
more bulky equipment. Furthermore the assembly can be produced very
economically and lends itself to many uses and applications which
have precluded the use of small, thin, light weight loudspeakers
and sound reproducing equipment heretofore.
Although the embodiment of the invention shown in the drawings and
described above represents one particular and preferred form of the
invention which has proven very successful in operation, it will be
apparent that numerous changes and modifications in the form,
construction and arrangement of the elements of the combination may
be made. In view thereof it should be understood that the
particular form of the invention disclosed herein is intended to be
illustrative only and is not intended to limit the scope of the
invention.
* * * * *