U.S. patent number 3,646,280 [Application Number 05/067,187] was granted by the patent office on 1972-02-29 for backplate for electret loudspeaker.
This patent grant is currently assigned to Pioneer Electronic Corporation. Invention is credited to Mitsuo Asahina, Kiyonori Iwama, Kensuke Okuda, Masahiko Tamura.
United States Patent |
3,646,280 |
Tamura , et al. |
February 29, 1972 |
BACKPLATE FOR ELECTRET LOUDSPEAKER
Abstract
An electrostatic electroacoustic transducer comprising a
vibrating film, an electret having many small holes and a fixed
electrode adhered closely thereto. The fixed electrode is made of
an electroconductive fiber.
Inventors: |
Tamura; Masahiko (Tokorozawa,
JA), Iwama; Kiyonori (Tokorozawa, JA),
Asahina; Mitsuo (Tokyo, JA), Okuda; Kensuke
(Tokyo, JA) |
Assignee: |
Pioneer Electronic Corporation
(Ohtaku, Tokyo, JA)
|
Family
ID: |
13349963 |
Appl.
No.: |
05/067,187 |
Filed: |
August 26, 1970 |
Foreign Application Priority Data
|
|
|
|
|
Aug 28, 1969 [JA] |
|
|
44/67613 |
|
Current U.S.
Class: |
381/191 |
Current CPC
Class: |
H04R
19/013 (20130101) |
Current International
Class: |
H04R
19/00 (20060101); H04R 19/01 (20060101); H04r
019/02 () |
Field of
Search: |
;179/111R,111E,106 |
Primary Examiner: Claffy; Kathleen H.
Assistant Examiner: Kundret; Thomas L.
Claims
What is claimed is:
1. An electrostatic electroacoustic transducer comprising a
vibrating film, an electret having one side juxtapositioned to said
vibrating film said electret having a plurality of holes therein
for passing acoustic radiation, a fixed electrode made of an
electroconductive fiber which is adhered to the other side of said
electret, and a pressing board pushing said fixed electrode against
said electret, said pressing board having a plurality of holes
therein for passing acoustic radiation.
2. An electrostatic electroacoustic transducer comprising a
vibrating film, two electets each having one side juxtapositioned
to said vibrating film each electret having a plurality of holes
therein for passing acoustic radiation, fixed electrodes made of an
electroconductive fiber said electrodes adhered to the other side
of each of said electrets, and pressing boards pushing said fixed
electrodes against said electrets, said pressing boards having a
plurality of holes therein for passing acoustic radiation.
3. An electrostatic electroacoustic transducer as set forth in
claim 1, wherein said electroconductive fiber is a carbon
fiber.
4. An electrostatic electroacoustic transducer as set forth in
claim 2, wherein said electroconductive fiber is a carbon
fiber.
5. An electrostatic electroacoustic transducer as set forth in
claim 1, further comprising a holding member for securing said
vibrating film, said electret and said pressing board together.
6. An electrostatic electroacoustic transducer as set forth in
claim 2, further comprising a holding member for securing said
vibrating film, said two electrets and said two pressing boards
together.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an electrostatic electroacoustic
transducer, and more particularly to an improvement of an
electrostatic electroacoustic transducer using an electret and
electroconductive fiber.
2. Description of the Prior Art
In prior art electrostatic electroacoustic transducers using
electrets, such as a push-pull speaker, a vibrating film is located
between two charged electrets. The electrets are affixed to fixed
electrodes and the device is held together by holding members. When
an alternating signal is applied to the fixed electrodes, the film
is vibrated and a sound is generated.
There are many disadvantages in prior art devices of this type.
First, it is difficult to uniformly adhere the electrets to the
fixed electrodes. Second, the position of the holes of the
electrets and that of the fixed electrode must coincide with each
other. It therefore requires great skill to adhere the electrets to
the fixed electrodes. Third, because of the difficulty of
construction in adding an acoustical adjusting function, it is
almost impossible to select an acoustical characteristic. Fourth,
if the device is not dustproof, the charging characteristics of the
electrets will deteriorate.
SUMMARY OF THE INVENTION
It is therefore the main object of this invention to provide a
novel and improved electrostatic electroacoustic transducer in
which the above-mentioned defects are solved.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional plane view of a prior art electrostatic
electroacoustic transducer using an electret.
FIG. 2 is a sectional plane view of the structure of an
electrostatic electroacoustic transducer of the preferred
embodiment of the present invention.
In prior art electrostatic electroacoustic transducers using an
electret, for example a push-pull speaker, are constructed as shown
in FIG. 1. A vibrating film 1 is located between charged electrets
2 and 3. Fixed electrodes 4 and 5 which are made of
electroconductive materials are adhered closely to electrets 2 and
3 respectively. They are firmly held in place by holding members 6
and 7. When an alternating signal is applied between the fixed
electrode 4 or 5 and an electrode 10, the vibrating film 1 is
vibrated whereby the sound generated is radiated through holes 8
and 9.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention will be explained in detail referring to FIG.
2 wherein the preferred embodiment of the present invention is
shown. Numeral 11 designates a vibrating film, the surface of which
is electroconductive. 12 and 13 show electrets having many holes
12a and 13a for the acoustic radiation. 14 and 15 show
electroconductive fibers. The electroconductive fiber may be, for
example, a carbon fiber, a graphite fiber, a metal fiber, or a
nonelectroconductive fiber such as a glass fiber which is coated
with metal or carbon so as to make it electroconductive. Further,
these fibers can be used singly or can be mixed with other
nonelectroconductive fibers. Usually, these fibers are used as
cloth being composed of single or mixed fibers in a sheet, net or
felt, which is hereinafter referred to as "a fiber." 16 and 17 are
insulated pressing boards having many holes 16a and 17a for the
acoustic radiation. 18 and 19 are rings having screw portions 18a
and 19a, whereby the fibers 14 and 15 are pressed toward the
electrets 12 and 13 through the pressing boards 16 and 17. Holding
members 20 and 21 are made of insulated materials and hold
above-mentioned components in place and have screw portions 20a and
21a whereby rings 18 and 19 are secured. An electrode 22 applies a
signal into the vibrating film 11, electrode 23 applies a signal
into the fiber 14, and electrode 24 applies a signal into the fiber
15.
The present invention has many improvements over prior art devices.
First, the electrets 12 and 13 can be manufactured with many holes,
having no relation to the fibers 14 and 15 which are the fixed
electrodes. Second, since the fibers 14 and 15 are between the
electrets 12 and 13 and the pressing boards 16 and 17, it is not
necessary to make the hole 12a precisely coincide with hole 16a and
the hole 13a with hole 17a. Therefore problems in making both holes
precisely coincide are solved and the level of efficiency of mass
production is raised. Third, as the fixed electrode (the fibers 14
and 15) is fibroid, the electrode can be pressed with the electret
12 or 13 equally on its whole surface. Fourth, the acoustic
characteristics can be selected by changing the elasticity or
thickness or length of the fibers 14 and 15, or by adjusting the
pressure of the pressing board 16 or 17 with the ring 18 or 19. If
it is unnecessary to adjust the pressure of the pressing board 16
and 17, rings 18 or 19 may be omitted and the pressing board 16 or
17 may be fixed to the holding member 20 or 21. In such case, the
level of efficiency of mass production is further increased. Fifth,
it is not necessary to provide a dustproof layer since the
electrets 12 and 13 are kept free of dust by fibers 14 and 15.
Therefore, the charge on the electrets lasts for many years.
* * * * *