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■ Electrostatic Speaker App. No. 49-1564 ■ Japanese Patent Application No. 45-36784)
Application No. 45 (1970) April 30 Priority claim [Facial] May 1969 沖 ア メ リ カ 208 8208
888 208 880 Inventor Lloyd Joseph・ Pops @ Applicant Lloyd Joseph Popp United States Glenn
State Tyson Ave Ave-443 same Chester Sea Pond Toiletstown Earl Day No. 2 Suffling Valley Road,
Bacchus County, Pennsylvania United States Agent Attorney Odajima Hirakichi
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front view of an electrostatic speaker with
features of the present invention. FIG. 2 is an enlarged partial sectional view taken along line 2-2
of FIG. 3 is an enlarged partial perspective view showing a frame structure and one corner of a
thin film constituting the electrostatic speaker of FIG. 1 with various components disassembled.
FIG. 4 is an enlarged partial perspective view showing the respective components shown in FIG. 3
assembled and further attached thereto (the other components shown in FIG.
Detailed Description of the Invention This application is directed to an improvement of an
electrostatic speaker of the type described in Japanese Patent Publication No. 51-6534. The
present invention separates a flexible thin film having a conductive coating from a substantially
rigid perforated backing plate and adjacent thereto, between the conductive coating [111111]
coating of the thin film and the backing plate. Relates to an electrostatic speaker of a type in
which a signal voltage is applied. In this type of electrostatic speaker, the sound is generated by
the movement of the flexible membrane relative to the perforated banking plate described above.
From a sound generation fidelity point of view, the perforated backing plate is such that the
vibrations caused by the sound waves generated by the movement of the membrane are
substantially eliminated in response to the applied signal voltage. It is desirable that they be
inherently rigid or damped. The main object of the present invention is to provide anti-vibration
means for a perforated backing plate of an electrostatic loudspeaker of the above type. According
to the invention, this object is achieved by pressing on at least a large part of the surface of the
perforated backing plate a slab of high cellularity made of plastic or resin material, for example a
slab of polyurethane foam. The use of such a foam isolation slab completely prevents the
vibration of the perforated backing plate and, in fact, the foam is acoustically transparent, so that
the perforated backing plate of the loudspeaker assembly. The inventors have found that the side
on which the is placed can be readily used to generate and propagate sound waves by the
vibration of the diaphragm or membrane behind the perforated backing plate. As described
above, since the foam vibration isolation slab is acoustically transparent, according to the present
invention, not only the perforated backing plate is provided with a broad vibration isolation
surface, but also the flexible thin film described above and the loudspeaker assembly It is also
possible to acoustically couple the other flexible membrane with the perforated backing plate
and the antivibration slab on the other side of the solid. A further general object of the invention
is to simplify the construction of a loudspeaker of the type described above. Part of this purpose
is used to pretension and clamp flexible thin films (a pair of flexible thin films in the case of a
double-sided speaker) during speaker assembly [111111] EndPage: 1 Is achieved by the frame
structure being When using a pair of flexible membranes, clamping the membranes should be
done with their conductive coatings facing each other and with the contact element between at
least part of the edges of the two membranes. Is preferred.
The assembly consisting of the frame structure as described above, the membrane and the
contact element is previously assembled as a subassembly, and this subassembly includes the
perforated backing plate and other parts including the anti-vibration slab, as well as the
membrane. A strip or the like to separate it from the perforated backing plate is assembled. Thus,
the construction of a loudspeaker of the above type is extremely simple and easy. Reference will
now be made in detail to the preferred embodiments of the invention with reference to the
accompanying drawings, which illustrate a speaker assembly with a pair of acoustically coupled
membranes. In the drawing, the frame structure consists of two opposed frames 5. These frames
are square in the illustrated embodiment flat and have an opening in the central part. As best
seen in FIG. 3, two parts, namely the central perforated contact strip 6 and a pair of flexible
membranes 7, are arranged between the two tub frames 5-5, each membrane It is arranged on
both sides of the contact strip 6. These films are preferably made of a thin resin material, such as
an ester resin sold by E. I. du Pont de Nimoas Acid Company under the trade name Mylar- ". The
thin film of the present invention is a very thin film, for example, preferably about 0.0061 iI / 1
to 0.012 m. Further, these thin films may be coated with, for example, a well-known vacuum
vapor deposition technique (wherein a gold-plated or conductive coating is deposited). Coating
(Aluminum is effective, the preferred 'Aluminum coating is very thin, and has a resistance of 3 to
5 Ohms per unit area of a sleeved thin film. The two thin films □ are arranged in such a way that
their conductive coatings face each other and thus engage the seven contact lip 6. On the outside
of the membrane 7, for example, a grip strip made of absorbent paper is provided with a gasket
8. After each component is crimped onto the perforated contact strip 6, the upper ship gasket 8
presses a part of the thin film '7 into the hole of the contact strip 6 as shown in FIG. Hold the thin
film with tension [111111] by tightening and holding firmly. As described in the abovementioned Japanese Patent Publication No. 51-6534, the thin film is preferably maintained in an
omnidirectional tension state. This makes the film to be formed into a thin film larger than the
thin film portion, gripping the edge portion of the film, and radially immaterial (a uniform tensile
force (e.g., about 1.) from the central portion of the film. It can be achieved by applying and
pulling 25 pounds of force.
When each part is placed and clamped between the frames 5-5 in a tensioned state of the thin
film, the clamping action of the frames results in the tension being maintained. In the illustrated
embodiment, the clamping shown at 9 and 10 is by means of a bolt, which clamps the frame 5-5
with the parts to be assembled therebetween to form a subassembly, and in this subassembly, in
particular FIG. Assemble the other parts in the manner described below with reference to. The
bolts 9 are used on the two opposite sides of the frame 5 and the bolts 10 are used on the other
two sides of the frame 5. In order to install the other parts in the above-mentioned subassembly
as will be explained below, the pole NO is in the form of studs which are threaded at both ends
and project on both sides of the subassembly. Referring to FIG. 4, in the central part of this
figure, a subassembly consisting of the parts shown in exploded view in FIG. 3 is shown in an
assembled state. In FIG. 4, said perforated backing plate is indicated at 11 and is shown in
exploded form on both sides of the subassembly. Between each backing plate 11 and the
membrane 7 there is, for example, a duster element 12 made of absorbent paper. This spacer
element can be distributed in various patterns over the entire surface of the backing plate, for
example, in the form of strips connected in a net-like or window-like manner as shown in the
figure, or pieces separated individually. 1.5 is included. A flange 13 having a cross section is also
provided around the spacer element 12 (see also FIG. 2), and the flange extends outward so as to
overlap the edge of the perforated banking plate 11, and the perforated backing plate It serves to
locate the center of the frame opening. The perforated backing plate provided on both sides of
the speaker assembly may use a single plate, but is preferably divided into a plurality of sections.
In the illustrated embodiment, each backing plate is divided into five sections or strips arranged
in two sections [111111] EndPage: two sections adjacent to one another as shown in FIGS. 1 and
4 '. It is done. The R-contacting edges of each backing plate are separated and electrically isolated
from one another so that the banking plates of each section can be separately connected to the
signal voltage supply system. Adhesive strips 14 are attached to each backing plate as shown in
FIGS. 1, 2 and 4 to hold the backing plates in the desired separated or spaced relationship.
Also, an adhesive may be applied to the spacer element 12 so that when the backing plate 11 and
the spacer element 12 are assembled, they adhere to each other. Further, as shown in FIGS. 1, 2
and 4, an adhesive coated strip 15 of material such as, for example, a blotter, is placed in the
center of each window of the mesh of spacer elements 12 for backing. It can also be attached to
the plate. Thus, a pair of banking plates and spacer elements can be assembled on both sides of
the loudspeaker assembly and placed inside the frame 5 with the spacer elements in contact with
the membrane. Next, a slab of cellular resin material, indicated at 16, is attached to the outer
surface of the backing plate 11. The slab 16 preferably extends over the entire loudspeaker area
inside the frame 5. This cellular slab is pressed onto the backing plate 11 by means of fasteners
in the form of a metal strip 17 in the embodiment shown. The main part of this fastener lies in a
plane perpendicular to the loudspeaker plane, but its ends 18 are twisted and have openings and
engage with the threaded projecting ends of the bolt 10 in the nutt It is fixed at 19. At the
connection between the strip 17 and the bolt 10, an insulating ferrule 20 is provided to
electrically insulate the two. Insulating the strip 17 in this manner is advantageous for the
following reasons. That is, while cellular materials are usually effective insulating materials, they
tend to temporarily accumulate sufficient moisture to form a leak path in certain conditions,
particularly in high humidity conditions. Thus, unless the strip 17 and the bolt 10 are electrically
isolated, an electrical leakage path between the backing plate 11 in contact with the cellular
material and the conductive coating of the thin film 7 in contact with the bolt 10 May be formed.
However, if the strip 11 and the [111111] rut 10 are electrically insulated, the above leak path
will not be formed even in a high humidity condition. As can be seen in FIG. 2, the cellular slab
16 (of about 2,2 crr L thickness, for example) is in contact with the entire surface of the
perforated backing plate 11. The cellular slab actually applies some pressure to the backing plate
to bring the spacer element 12 into contact with the outer surface of the membrane. The outside
of the two membranes is provided so that the pressure exerted by this cellular slab "ramps" the
two membranes 7 together between the spacer elements 12 as shown in FIG. Preferably, they are
aligned with one another.
The above pressure is not large, nor is it necessary, but it may be sufficient to provide the
backing plate itself with the desired anti-vibration effect. The appropriate force to be applied at
each of the retaining nuts 19 will be on the order of 1.5 pounds. The damping action in the
arrangement of the parts mentioned above is mainly achieved by the engagement between the
cellular slab and the perforated backing plate, but the edge portion of the perforated backing
plate and the limited strip portion and the spacer element 12 and the small pieces It is also
achieved by engagement with F.15. Thus, the two membranes of the illustrated or described
double-sided or push-pull loudspeaker are clamped together under the action of the cellular slab
and the spacer element on the backing plate, but these membranes are used during the use of the
loudspeaker Are mutually separated in substantially all regions of the thin film between the
facing spacer elements 12 and the small pieces 15. This separation occurs, for example, as a
result of the bias field created by the bias voltage applied between the perforated backing plate
and the conductive coating on the membrane. Adjacent thin films are attracted toward each
backing plate by the action of the bias voltage. The separation of the films in the various film
areas is shown in FIG. It should be noted that the space between the two thin films is a vented
space rather than a sealed space in connection with thin film separation by the bias electric field.
In fact, the space between the thin films is breathable, even though the thin films are in contact
with each other in a limited area 5 between the spacer elements on both sides of the speaker
assembly. This breathability is ensured by defining a space, for example as indicated at 21 in FIG.
3, between the perforated contact strips 6 which are clamped together with the membrane 7 by
means of the frame 5 and with [111111] EndPage: 3. Also, since the engagement pressure
applied to the membrane by the spacer element 12 is not large, and the spacer element 12 is
advantageously formed of a fibrous material such as a blotter, the membrane and the spacer
element are engaged. The air flow between the thin films easily occurs even in the If necessary to
further ensure such membrane air space permeability, the spacer elements can be provided with
embossed grooves as shown at 22 in FIG. As described above, the arrangement of the
components including the thin film (this pressure is applied to bring the two thin films close to
each other, and further includes spacer elements for bringing the two thin films into contact with
each other) It is preferred from the point of view of protecting the matching conductive coating.
The considerable limitation of the vent cross-section is advantageous in avoiding adverse effects
on the metallic coating. At the same time (here, it is important to ensure that the thin film space
is not sealed, to ensure the desired operation of the loudspeaker, for example to allow free use of
the loudspeaker where the barometric pressure changes, such as in the cabin of an aircraft) Is
also important. The pressure between the thin film and the pressure outside the thin film is not
easily equal and therefore does not interfere with the desired operation of the loudspeaker. The
arrangement of the components described above is also important in that the distance between
the thin films of the double-sided electrostatic speaker can be kept narrower than in the
conventional possible distance, thereby reducing the total volume of the air layer between the
thin films. Acoustic coupling between the thin films can be increased. In fact, the above-described
system for contacting the cellular slab over the entire surface of the backing plate to dampen the
backing plate is also extremely advantageous for the following reasons. That is, not only does the
vibration isolation by the cellular slab prevent unwanted resonance of the backing plate, but also
by placing the vibration isolation slabs on both sides of the speaker assembly and providing
means for clamping the thin film between them And the backing plate associated with it are
uniformly spaced. Make the interval uniform like this. That is important because at the lower end
of the frequency response range a uniform output is obtained over the entire surface of the
loudspeaker. If the spacing between the backing plate and the active area of the membrane is not
uniform, it may limit the low frequency [111111] possible output of the speaker. As described in
the above-mentioned Japanese Patent Publication No. 51-6534, signal voltages are supplied in a
push-pull manner to two loudspeakers which are acoustically coupled to each other in the
loudspeaker assembly. Of course, this signal voltage is superimposed on the bias voltage as is
known in the field of electrostatic speakers. Although only one backing plate may be provided on
each side of the speaker assembly, the backing plate may be divided as described above, and the
divided plates may be described in, for example, Japanese Patent Publication No. 51-6534. The
signal voltage can be supplied separately via the electrical network. As shown in FIG. 1, an
electrical connection 23 is extended from each backing plate, and used by connecting to each
backing plate, or the electric network shown in the above-mentioned Japanese Patent Publication
No. 51-6534 or other desired The bias voltage can be supplied via this electrical network to the
connection 25 extending from one of the contact strips 6 between the coated surfaces of the
membrane 7.
Turning now to the spacer elements 12 and the peripheral flange 13 provided around the mesh,
the whole of the mesh spacer structure can be made by stamping from the remaining central
portion of the sheet forming the gasket 8. . The gasket 8 (see FIG. 3) is an element positioned on
the outer surface of the edge portion of the membrane for clamping the membrane on the
contact strip 6. As can be seen from FIG. 1, FIG. 3 and FIG. 4, holes 26 are provided in any part of
the speaker frame 5, but these holes also serve for various intermediate parts to be clamped
between the frames 5. It is provided and used, for example, when installing a speaker in a
speaker cabinet. Also, as shown in FIG. 3, 1, there is no hole at the corner of the thin film T
whose center coincides with the hole 26 of the above frame, but the parts are assembled and the
mounting is made by bolts or When a screw is inserted, the membrane can be easily drilled to
allow the most recent or screw to pass through. In this way, the attachment is formed at the
corner of each part to pass the bolt. □ It is desirable and desirable to provide an insulating
sleeve in the drilled hole so that the bolt does not contact the thin film or contact strip. . Next, the
cellular slab 16 will be described. [111111] EndPage: 4 (This is a polyurethane foam as
described above. The foam used is preferably an open cell or pore structure which is widely
interconnected and interconnected between the cells, and the pores are considerably large, so
that this cell structure is relatively thin without having a membrane or cell wall in between It is
substantially similar to a skeleton or loose mesh of fragmented skeleton strands. For the
purposes of the present invention (this suitable representative polyurethane foam has an average
of 25 pores per about 2.5 crIL. Although various resin or plastic foam materials can be used,
polyurethane is particularly effective, and in the case of the above polyurethane foam, from the
result of acoustic measurement when it is placed between and without It was found to be
acoustically transparent so that the presence of polyurethane foam could not be detected. The
weight of a typical polyurethane foam used in accordance with the present invention is on the
order of only 870 grams (31 ounces) per about 30 Crr L square (1 cubic foot). Although the
cellular slab as described above is light in weight and has high skeletal properties, the perforated
backing plate (the anti-vibration action against the plate is very effective in eliminating the
backing plate's vibration, As a result, the adverse effect of the vibration of the backing plate and
the generation of distorted noise are prevented.
The deflections that occur as a result of the vibration of the banking plate do not merely stretch
or shrink the damping material in a plane parallel to the backing plate, but rather create a
compression or bending action within the damping material, thus preventing Locating material
between the backing plate on one side and the series of fasteners on the other side increases its
efficiency and effectiveness. It is very advantageous from the point of view of the manufacturing
technology that the mounting of the perforated backing plate 11 and the spacer 12 and the
attachment of the cellular slab 16 be separate from gripping or clamping the diaphragm thin film
γ of the frame. . Since the membrane is initially tensioned and then the membrane is clamped
between the frames, the frame and membrane subassembly can be removed for this task
(immediately from the apparatus and jig used, Other parts can then be attached to the above
subassembly at another work site. In this way, there is no need to perform other operations in
the device for pulling the thin film and clamping it between the frames, so the manufacturing
ability of the device for pulling and installing the thin film can be increased. Another advantage
of the frame and membrane subassembly is that the membrane's vibration mode can be tested
before testing on the final assembly, which improves quality control. Since the other elements
subsequently applied to the above assembly are mechanical in nature and thus only require
control of their placement, size and pressure, the final potential is to be predicted very accurately
Can. In the case of the specific embodiment shown and described the banking plate and its
attachment to the vibration damping element described above, i.e., a foam which substantially
covers the entire surface of each backing plate as a vibration damping means on both sides of the
loudspeaker assembly. Not only is it advantageous to have a single slab of material, but it also
comprises smaller elements as anti-vibration means, i.e. strips or the like that can only engage
the edge portion of the backing plate. The case is also advantageous. The arrangement according
to the invention makes it easy to assemble frame assemblies which can incorporate thin films of
different tensions or different thicknesses in order to meet different acoustical requirements and
backing plates with different shapes and spacings. It also has the advantage of being able to be
combined. As mentioned above, another advantage of the arrangement incorporating the slabs of
cellular material on both sides of the loudspeaker is that not only the cellular slab is acoustically
transparent, but it is also highly charged and thus prone to attract dust in the air Alternatively,
the slab also has a function as a filter to prevent dust from adhering to the thin film.
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