U.S. patent number 3,779,336 [Application Number 05/266,552] was granted by the patent office on 1973-12-18 for diaphragm for sound transducers, method and apparatus for manufacturing it.
Invention is credited to Jose Juan Bertagni.
United States Patent |
3,779,336 |
Bertagni |
December 18, 1973 |
DIAPHRAGM FOR SOUND TRANSDUCERS, METHOD AND APPARATUS FOR
MANUFACTURING IT
Abstract
Diaphragm for sound transducers and a method for manufacturing
it, including providing a cellular plate-like member molded of
granular starting material and defining a provisional flat front
face and a rear face. A layer including said provisional flat front
face is heat severed from the plate-like member, whereby a new
concavely shaped front face and plate-like member is defined, where
the contiguous severed cells become sealed in themselves and sealed
together at the same time as they are subject to stresses and
provide a hardened surface. Preferably a sheet-like member is
adhered to the new front face and the curved plate-like member is
then urged into substantially planar condition, whereby the
sheet-like member becomes stressed and the severed cells of the new
front face are subject to additional stresses, so that the
resulting diaphragm has a flat front face under a higher stress
than the successive cells defining said diaphragm from said front
face towards said rear face, the stresses progressively decreasing
from said front face towards said rear face. The invention relates
also to an apparatus for severing the layer including said
provisional front face, from the rest of the plate-like member.
Inventors: |
Bertagni; Jose Juan (Buenos
Aires, AR) |
Family
ID: |
23015050 |
Appl.
No.: |
05/266,552 |
Filed: |
June 27, 1972 |
Current U.S.
Class: |
181/174 |
Current CPC
Class: |
H04R
7/04 (20130101) |
Current International
Class: |
H04R
7/00 (20060101); H04R 7/04 (20060101); G10k
013/00 (); H04r 007/00 () |
Field of
Search: |
;181/31B,32R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Tomsky; Stephen J.
Claims
I claim:
1. A diaphragm to be used in sound transducers, comprising a
strong, stiff, plastics plate-like member formed by a continuous
structure of cells and having a sealed front face, a rear face and
side faces connecting said front and rear faces, the cells defining
said front face being under a higher stress than the successive
cells defining said diaphragm from said front face towards said
rear face, the stresses progressively decreasing from said front
face towards said rear face, and the surface defining said front
face being a hardened skin-like surface integral with said
plate-like member and sealing said front face, said skin-like
surface having been obtained by heat severing.
2. The diaphragm of claim 1, wherein said heat severed and sealed
front face is concavely shaped.
3. The diaphragm of claim 1, wherein said front face is
substantially planar, said diaphragm being a substantially flat
diaphragm, and including a tensioned sheet-like member adhered to
said front face and a frame for said diaphragm, said diaphragm
being connected to said frame.
4. The diaphragm of claim 3, wherein said sheet-like member is also
adhered to said side faces and said frame supports and maintains
said diaphragm in substantially flat position with the
substantially straight front face.
5. The diaphragm of claim 4, wherein said rear face defines a
marginal vibration damping portion circumscribing a pinna of the
human ear shaped figure portion, said figure portion including a
central portion which is stiffer than the remainder of the figure
portion and which is located within a zone of the figure portion
which is out of the geometric center thereof, said stiffer portion
forming a center for collecting vibrations and an endless channel
having a bottom wall adjacent said front face connecting the
periphery of said figure portion with said marginal vibration
damping portion.
6. The diaphragm of claim 1, wherein said front face is
substantially planar, said diaphragm being a substantially flat
diaphragm, and including a sheet-like member adhered to said front
face and a frame for said diaphragm, said diaphragm being connected
to said frame.
7. The diaphragm of claim 1, wherein said front face is
substantially planar, said diaphragm being a substantially flat
diaphragm, and including a sheet-like member in front of said front
face and a frame, said sheet-like member being supported by said
frame, said diaphragm being connected to said frame and arranged
beneath said sheet-like member in said frame.
8. The diaphragm of claim 1, wherein said rear face defines a
marginal vibration damping portion circumscribing a figure portion,
said figure portion including a central portion which is stiffer
than the remainder of the figure portion and which is located
within a zone of the figure portion which is out of the geometric
center thereof, said stiffer portion forming a center for
collecting vibrations.
9. The diaphragm of claim 8, wherein said rear face includes an
endless channel having a bottom wall adjacent said front face and
connecting the periphery of said figure portion of said marginal
vibration damping portion.
10. The diaphragm of claim 8, wherein said front face is
substantially planar, thereby defining a substantially flat
diaphragm.
11. The diaphragm of claim 9, wherein said front face is
substantially planar, thereby defining a substantially flat
diaphragm.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention refers to a diaphragm to be used in sound
transducers, to a method for manufacturing said diaphragm and to an
apparatus for severing a layer of material from the diaphragm. More
particularly, the present invention is mainly used in connection
with so-called flat loudspeakers which provide an excellent high
fidelity reproduction of sound, although it may likewise be used in
connection with the manufacture of microphones.
In the following description, reference will be mainly made to the
diaphragm of a loudspeaker, although the invention is likewise
applicable to microphones.
2. Description of the Prior Art
It is well known in the vibration transducing art for moving coil
loudspeakers or microphones, that either the coil has to vibrate
the diaphragm (in the case of a loudspeaker) or the diaphragm has
to receive the vibrations and transmit them to the coil (in the
case of a microphone). In both cases, the diaphragm is resiliently
supported by its edge or marginal portion and has to vibrate in a
plane substantially perpendicular to the axis of the coil. In other
words, the coil (hereinafter called the "voice coil") drives or is
driven by the diaphragm in a plunger-like manner. Thus a mass of
air is required in front of and behind the diaphragm and is moved
thereby.
Attempts have recently been made to replace the conical diaphragm
configuration, wherein the conical diaphragm is formed from paper
pulp or the like, by a flat diaphragm made of an expanded cellular
plastics material such as polystyrene, wherein the voice coil is
mounted in a hole in the diaphragm or in a recess in said
diaphragm, and the diaphragm, as such, operates in a plunger-like
forward and backward vibratory manner, as in the well known
above-mentioned conical diaphragms. Attempts have also been made to
provide a flat diaphragm with a central funnel-shaped portion
having a hole therein, in which the voice coil is secured. While
all these flat loudspeaker embodiments operate on the same
principle as the above-mentioned conical loudspeakers, the housings
for these flat loudspeakers are smaller in depth.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a diaphragm
to be used in sound transducers, comprising a strong, stiff,
plastics plate-like member formed by a continuous structure of
cells and having a heat severed and sealed front face, a rear face
and side faces connecting said front and rear faces, the cells
defining said front face being under a higher stress than the
successive cells defining said diaphragm from said front face
towards said rear face, the stresses progressively decreasing from
said front face towards said rear face and the surface defining
said front face is hardened.
The invention relates also to a method for manufacturing a
diaphragm to be used in sound transducers made of a cellular,
strong, stiff plate-like member, having a front face, a rear face
and side faces connecting said front and rear faces, said method
comprises the steps of molding granular starting material to form a
granular expanded-bonded, cellular, strong, heat-severable,
plastics plate-like member having a provisional flat front face,
said rear face and said side faces which connect said provisional
flat front face with said rear face, said plate-like member
defining a marginal vibration damping portion substantially
circumscribing a figure portion on the rear face, said figure
portion including zones of lesser thickness than said marginal
vibration damping portion; severing a layer including said
provisional flat front face by means of a heated, substantially
filiform member by relatively moving said heated substantially
filiform member through said plate-like member and thereby sealing
and contracting the severed granules defining the new front face,
whereby the resulting plate-like member becomes curved with a
concave substantially integrally sealed front face which is
hardened.
Further, according to the invention, there is provided an apparatus
for severing a cellular strong stiff plastics plate-like member to
be used as a diaphragm, having a front face and a rear face,
comprising a track, a heated substantially filiform member
traversing said track and means for maintaining said substantially
filiform member under tension.
More particularly, the filiform member is an electric wire
conductor which is height adjustably mounted with regard to said
track and at least one pressure means upstream of said electric
wire conductor above said track adapted to urge on the plate-like
member to be moved along said track in order to severe a layer
therefrom.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is illustrated by way of example in the accompanying
drawings, in which:
FIG. 1 is a perspective view showing a particular embodiment of a
diaphragm in accordance with the present invention.
FIG. 2 is a cross-section according to line A--A of FIG. 1.
FIG. 3 is a diaphragm showing the granular arrangement of an
expanded bonded cellular strong stiff plastics plate-like
member.
FIG. 4 is a diagram showing the behaviour of the cells if from the
plate-like member of FIG. 1 a top layer were to be cut by means of
a cold cutter, such as a knife or a saw. This embodiment does not
form part of the present invention.
FIGS. 5, 6 and 7 are respective explicative diagrams showing the
behaviour of one cell which is being cut by a heated filiform
member.
FIG. 8 is a diagram showing a heat severed concave-shaped
plate-like member.
FIG. 9 is an actual cross-section of a concave-shaped diaphragm.
FIG. 10 is a cross-sectional view of the same diaphragm of FIG. 9
which is subject to additional steps of the method of manufacture,
in accordance with a further developed embodiment of the present
invention.
FIG. 11 is a cross-sectional view showing the finished diaphragm
mounted in a frame.
FIG. 12 is a detail in cross-sectional view of an alternative
embodiment with regard to the one shown in FIG. 11.
FIG. 13 is a schematic perspective view of an apparatus for
severing a plastics plate-like member to produce the diaphragm in
accordance with the invention.
FIG. 14 is a diagram showing an alternative embodiment as far as
the roller means are concerned in connection with the apparatus for
severing a plastics plate-like member, to produce the diaphragm in
accordance with the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
With regard to the particular embodiment shown in FIGS. 1 and 2,
there is shown a plate-like member 71, which is a diaphragm which
has, as will be later better explained, a heat severed and solid
front face 72 which is hardened and a rear face comprising a
marginal vibration damping portion 73 and a central figure portion
74 which has approximately the shape of the pinna of the human ear.
Within the central zone of said figure portion 74, but out of the
geometric center thereof, there is a recess 75 which corresponds
also to the thickest portion of the figure portion 74 and into
which end a pair of parallel channels 76, 76'. The periphery of the
figure portion 74 is preferably of smaller thickness than the rest
of the figure portion 74 and ends into an endless channel member 77
whose bottom wall 77' is to be as near as possible to the front
face 72. As will be later explained, special expedients have to be
provided in order to achieve the arrangement as shown in FIG. 2.
The endless channel member 77 connects the periphery of the figure
portion 74 with an edge or side wall 78 which ends in the marginal
vibration damping portion 73.
An electromagnetic unit 79 for driving the diaphragm if the
assembly operates as a loudspeaker, is schematically shown as a
capsule having a pair of electric conductors 80, 80'. Unit 79 is to
be housed into recess 75 and the conductors 80, 80' are to be
housed in channel 76, 76', respectively, to be there connected to a
suitable electronic circuit (not shown). Upon using the assembly as
a loudspeaker, unit 79 will vibrate the figure portion 74 and
thereby generate sounds, the sound generating waves of which will
be blocked from movement into the marginal vibration damping
portion 73 by the endless channel member 77. Preferably, the
central portion including the recess 75 is stiffer than the
remainder of the figure portion 74, which will improve the sound
reproduction in the high frequency ranges.
The diaphragm shown in the embodiment of FIGS. 1 and 2 is
manufactured by molding granular starting material to form -- as
shown in FIG. 3 -- a granular expanded-bonded cellular, strong,
stiff plastics plate-like member, conveniently made of polystyrene
or polyurethane. The plate-like member 22 consists of expanded
granules 20 which, although in FIG. 3 they are shown as all being
of substantially the same size, are in practice, not so uniform.
These granules 20 are welded or fused together forming in between
them alveolar cells 21 which contain moisture produced during the
production of the plate-like member 22. The granules 20 are
somewhat resilient. The plate-like member 22 has a substantially
parallellepipedic shape and comprises a front face 23, rear face 24
and side faces 25. For the purpose of this invention it may be
considered that between the front face 23 and the rear face 24 a
number of layers are formed which for convenience of explanation
will be defined by the rows of granules shown in FIG. 3. Thus, the
front face 23 which defines a provisional front face is defined by
a front face layer 26, the rear face 24 forms part of a rear face
layer 27 and there are in between the layers 26 and 27 a number of
intermediate layers 28, 29 and 30. Obviously in practice each layer
may be formed of more than one row of granules and the granules
will not be so perfectly aligned in rows as shown in FIG. 3. Due to
the fact that the granules 20 are somewhat resilient and in between
the granules there are the alveolar cells 21, the plate-like member
22 exhibits internal damping, if a percussion force or a vibratory
movement is, for instance, applied to the rear face 24, as
indicated by arrow 31.
To achieve good sound reproduction it is however desirable to
eliminate as far as possible this damping effect which tends to
produce distortion and reduce output.
To obtain a better output, it is advisable to remove the moisture
at least from the cells facing the front face and the way this is
achieved will be described later on.
There is, however, another aspect of the invention which has to be
first dealt with. The granules, i.e., the granular starting
material, which are to be housed in a mold in order to mold the
plate-like member 71, have a certain minimum size which is being
heat expanded upon molding the plate-like member. However, the
layer of granules which have to be housed in the mold cannot be
below a predetermined height since otherwise, upon molding the rear
face 73, 74 of the plate-like member, the male stamp must remain at
a certain distance from the bottom of the female mold, so that in
the zone corresponding to the bottom wall 77' of the endless
channel member 77, a sufficient height is maintained to assure that
the plate-like member 71 has a continuous uninterrupted front face
81. To this end it is first necessary to mold a plate-like member
71 having a height as the one defined in FIG. 2 between the rear
face defined by the marginal vibration damping portion 73 and the
provisional front face 81 shown only in dotted lines. The resulting
product is however not an optimum product, because the distance
existing between the bottom wall 77' and the provisional front face
81 is too great and vibrations, particularly those corresponding to
the low frequencies, would have a tendency to propagate through
this portion, by-passing the endless channel member 77 and entering
into the marginal vibration damping portion 73, which tends to
produce distortions and reduce output.
It has been first thought to simply slice off a layer including
said provisional front face 81 and corresponding to the portion
between the front face 72 and the provisional front face 81. If the
slicing would be carried out for instance by a cold knife or a saw,
then -- at least theoretically speaking -- the front face layer 26
would be cut into two halves, whereby one half, namely the front
face layer 26' would adopt the shape as shown in FIG. 4. By
proceeding along this line, the alveolar cells 21 of the front face
23 would be eliminated, provided that the severing could be carried
out through those portions where the expanded granules are welded
together. This would improve the output and reduce the distortions
in a small proportion which is neither sufficient nor optimum.
If additional moisture present in other cells 21 could be removed,
this would of course improve the qualities of the end product. It
has therefore been thought that the severing should be performed by
means of a heated filiform member, such as for instance a heated
electric wire. The heat would then remove also an additional
proportion of moisture present in underlying cells 21. Upon
carrying out the tests, several unforeseeable, very surprising
results were obtained and which will now be explained in connection
with FIGS. 5 to 8, whereby in addition to the removal of the
moisture, the resulting front face becomes automatically under a
higher stress than the successive granules of the intermediate
layers 28, 29, 30 and rear face layer 27. Due to the creation of
these stresses, the resulting plate-like member becomes of concave
shape as shown in FIG. 8 and also in FIG. 9 which represents the
actual shape of the diaphragm including the features of the rear
face as explained in connection with FIG. 1. In addition, the
surface defining said front face 72 becomes sealed and
hardened.
In order to explain the results which were achieved by the tests,
reference will now be made to a theory which has been deduced from
the results of the tests and which is believed to be the reason for
achieving such an unforeseeable result. To explain this theory,
reference will first be made to a single expanded granule 20', as
shown in FIG. 5, which before being subject to the heat severing
process, will for this theory be considered as if it were a
substantially perfect sphere, as indicated in part by dotted line
82. Axis line 83 indicates a cutting plane through which the
electrically heated wire 84 is to move.
It has to be borne in mind that the granule 20', if made for
instance of polystyrene, upon being cut by heat, produce at the
cutting surface fiber-like filaments which melt due to the heat and
form thereby a new layer at the heat severed surface. As soon as
the heated wire 84 enters in contact with the granule 20', there is
a retraction -- bearing in mind that it is an expanded granule --
of the granule in the zone adjacent the wire 84, which can be seen
in FIG. 5 by comparing the full line drawing with the dotted line
82. This movement is somewhat resisted particularly by the lower
portion of the granule due to the fact that it has to be recalled
that the lower portion of the front face layer 26 -- see also 26'
of FIG. 4 -- is connected to the next intermediate layer 28 which
are also subject to the heat effect, so that the moisture present
in the adjacent cells 21 is at the same time substantially
removed.
As the wire 84 continues its movement, as shown in FIG. 6, those
fibers which tend to be formed adjacent the cutting zone, by the
same heat, fall onto the cut portion, thereby increasing the
thickness of this layer and hardening the same. This is represented
by means of a thicker line 85 which, for simplicity, has likewise
been shown in the upper portion, although in practice the upper
portion is of no importance because the sliced-off part which
corresponds to the section encircled by the dotted line in FIG. 2
is disposed of. The forward movement of the heated wire 84 produces
an additional tensile stress in the direction of movement of the
wire 84 along the granule 20', so that the "end" 86 moves further
away from the dotted line 82. This process is continued -- FIG. 7
-- until the heated wire 84 has passed through the granule 20'
dividing the latter into two halves 20a, 20b. The lower half 20a
has a concave-shaped severed surface 86 created by the stresses and
the same is true for the upper half 20b, although the latter, since
it is not linked to the additional intermediate layers, has a
tendency to return to its original shape due to the memory of the
material. The lower half 20a remains with a higher stress because
due to the heat effect the immediate adjacent granules have
likewise changed their shape. This stress, as will be later
explained in connection with FIG. 8, changes also the shape of the
immediate adjacent layers 28, 29, 30 of granules -- see FIG. 8. If
the process just described is repeated through a chain of welded
adjacent granules, a shrinking tendency is produced, which
transforms the flat-plane plate-like member 22, into a
concave-shaped plate-like member 87, as shown in FIG. 8. The
severed front layer 26" is the one which shrinks most while the
rear face layer 27 has not been substantially subject to any
transformation. Therefore, the plate-like member behaves like a
loaded beam member resting on spaced apart supports, at least up to
the neutral line thereof. Thus, automatically, the successive
layers 28, 29, 30 and 27, defining successive rows of cells have
progressively decreasing stresses from the front face 72' towards
the rear face 24'. This method further automatically seals the
front face 72'. Thus, no extra sealing step is necessary, at least
as far as the front face 72' is concerned. Therefore, as a result
of the method, the surface defining the front face 72' is a
hardened skin-like surface integral with said plate-like member 22
and sealing the front face.
While FIG. 8 merely shows the behaviour of the granules of the
different rows to illustrate the progressively decreasing stress
arrangement, it will readily be understood that in practice the
resulting diaphram 88 will have the shape as shown in FIG. 9, where
the bottom wall member 77' is now at the smallest possible distance
with regard to the front face 72'. By "smallest possible distance"
is to be understood that a thickness is provided which allows the
figure portion 74 to vibrate without a breakage occurring in the
portion adjacent the bottom wall member 77'. This size cannot be
achieved by direct molding, but only by severing the exceedent
layer in the way as just explained.
Tests have been made with the diaphragm 88 of FIG. 9, to which the
electromagnetic unit 79 -- see FIG. 1 -- has been attached and the
results achieved may be classified as "quite good." The fact that
the front face 72' is hardened is an additional feature which
increases the stresses, bearing in mind that the quality of the
sound reproduction will become better if the stresses in the front
face are increased, so that said front face will act as a tensioned
height of a drum.
To this end, as shown in FIG. 10, the front face is covered with a
sheet member 32 having marginal portions 33 projecting beyond the
front face 72'.
The sheet member 32 may for instance be made of paper or fabric.
The face opposite the one to be adhered to the front face 72' may
have a suitable decoration or design.
It is now possible to apply to the granules 20 a second stress,
parallel to the planes defined by the layers. To this end, the
curved plate-like member of FIG. 10 is now urged, with the adhered
sheet-like member 32, into substantially planar condition as shown
in FIG. 11. Since the granules are now also tensioned in planes
parallel to their layer, they will become somewhat more flattened,
so that thereby the total thickness of the plate-like member 22 is
further reduced. Simultaneously, the sheet member 32 is also
stretched in its own plane and in order to anchor the sheet member
in its stretched state, the marginal portions 33 are now adhered at
least to the side faces 25. If the length of the marginal portions
33 is somewhat larger, they may be turned over to cover the edge
portions of the rear face 24, without degrading the resulting
diaphragm.
Thus, a flat diaphragm with pre-tensioned layers is obtained, in
which the tension gradually decreases from layer to layer between
the front face and the rear face. The diaphragm is kept flat by
linking it to a frame 89.
The double tensioned diaphragm 71, as shown in FIGS. 1 and 11,
provides therefore a still better result in sound reproduction. For
clarity purposes, in FIG. 1 the frame 89 has not been shown.
The embodiment of FIG. 12 differs over the embodiment of FIG. 11 in
that the double tensioned diaphragm 71' has been urged to a
substantial planar condition by means of frame 89' without the
diaphragm having adhered thereto the sheet member. If desired, a,
preferably pre-tensioned, sheet-like member 32' is stressed on the
frame 89' above, and preferably spaced apart from, the front face
72'. This sheet-like member 32' is provided for decorative purpose,
although if the spacing between said sheet member 32' and the front
face 72' is reduced to a minimum, they enter in cooperative
relationship if the vibrations are substantial upon the front face
72' contacting the sheet member 32'.
In FIG. 13 an apparatus is shown which can be used for severing the
plate-like member according to the method as previously described.
The apparatus comprises a U-shaped casing 90 defining a track 91 on
which a conveyor platform 92 moves forward and backward by means of
a schematically indicated driving arrangement 93. This driving
arrangement 93 consists of a driving roller 94 and a driven roller
95 having cable means 96 linked to the conveyor platform 92 to move
the latter in either of the directions as indicated by double arrow
97. Above track 91 preferably a roller 98 in height adjustably
arranged in schematically shown bearings 99. Downstream of roller
98, a heated filiform member, more particularly an electric wire
100 is arranged between a stationary height adjustable post 101 and
a roller 102 over which said wire 100 runs and supports at its free
end a weight 103. Thus, the wire 100 is always under a suitable
tension. Roller 102 as well as post 101 are connected through wires
104 and 105 to an electricity supply source 106. Roller 102 is
likewise height adjustably supported by casing 90 only
schematically indicated by double arrow 107. Air cooling nozzles
108, 109, are provided adjacent the post 101 and roller 102.
The operation of the apparatus is as follows: the platform 92 is
moved upstream beyond the roller 98 and a plate-like member is
mounted on said platform 92 which is now moved downstream passing
by the roller 98 which exerts a slight pressure on the front face
23 to bypass the electrically heated wire 100 and severe the upper
layer, whereby the front face 72' is formed at the same time as the
resulting diaphragm becomes concavely shaped, to result in a
product as shown in FIG. 9. The diaphragm 88 is unloaded then from
the platform 92 and subject to further treatments, as explained in
connection with FIGS. 10 and 11 as previously explained. The
platform is then moved upstream to receive a new load. It can be
readily conceived that if two rollers 98 are provided on each side
of the electric wire 100, that then during each stroke a working
operation may be performed, provided that the other roller is
withdrawn to become inoperative.
The system of the platform 92 is merely illustrative. It could be
replaced by rollers such as shown in FIG. 14. More particularly,
the bottom rollers 110, 111, move the plate-like member 22 in the
direction indicated by arrow 112 and the arrangement of rollers 110
and 111 with regard to the electric wire 100' and the top roller
98' can be such that a cooperation in the tendency of forming the
concave-shape is achieved by arranging roller 111 in a slightly
higher plane than roller 110, as shown by the two
dot-and-dash-lines 113, 114.
Obviously, an apparatus could be provided where the electric wire
moves with regard to the plate-like member to be severed; in other
words, a relative movement between the wire and the plate-like
member must be provided.
In the several embodiments hereinabove described, the
electromagnetic unit 79 is housed in recess 75, which is located in
the rear face portion; however, nothing speaks against the
possibility that the electromagnetic unit 79 is connected to the
hardened front face 72'.
It is also possible to coat the marginal vibration damping portion
73 with a hardening layer, for instance a vinylic layer, and to
connect thereto a second electromagnetic unit (not shown) which is
particularly operable in the high frequency range, so as to have a
more pronounced sound reproduction for the high pitches. Thus, a
more generic concept is that the diaphragm should have a stressed
layer for increasing the quality of the sound production.
It will be obvious that modifications may be introduced in this
invention upon carrying it out into practice as far as certain
structural details are concerned but always without departing from
the fundamental principles which are clearly specified in the
following claims:
* * * * *