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Description of Invention
Electret electrostatic speaker
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electret
electrostatic speaker comprising a diaphragm and a pair of fixed electrodes sandwiching the
diaphragm from the front and back. Heretofore, electret electrostatic loudspeakers have been
well known, in which a flat diaphragm is driven by a fixed flat plate electrode from the front to
the rear and between pores. An example of the operation principle is shown in FIG. The film 1 of
monoball electret, which holds a single charge (in this example, a negative charge)
semipermanently, is used as a vibrating film, and the fixed electrodes 2 and 3 are disposed before
and after that. The fixed electrode and the vibrating film form a capacitor, and a positive charge
is induced on the surface of the fixed electrode. A signal voltage whose phase is inverted is
applied to the front and rear electrodes 2 and 3 to push-pull drive the vibrating membrane 1 by
electrostatic force. The acoustic vibration generated by the vibrating membrane is radiated back
and forth through the pores of the wedge / fixed electrode. In another conventional example, as
shown in FIG. 2, the film 5 coated with the conductive coating 4 is used as a vibrating film, and
the polarization is semipermanently held on the metal electrode 6.7 before and after. In the case
of the conventional Electric EndPage: 1 treads 8 and 9, in this example, the fixed electrodes are
disposed with the negative charge side facing the vibrating membrane. The vibrating membrane
and the fixed electrode form a capacitor as in the previous example, and a positive charge is
induced on the surface of the vibrating membrane by the voltage of the electret. The diaphragm
is push-pull driven by the phase-inverted input voltage. Acoustic vibrations are also emitted back
and forth through the pores which are drilled in the stationary electrode. However, in the case of
the conventional electrostatic speaker, it is necessary to increase the amplitude between the fixed
electrode and the vibrating film in order to reproduce the low-pitched range, so that the gap
between the fixed electrode and the diaphragm must be increased. It has the disadvantage of
having to give up reproduction in the low range or having to take a very large area of the
vibrating film because it becomes very bad. The present invention has the above-mentioned
conventional drawbacks by applying to the electret electrostatic type speaker the same
pronunciation tit = as used in the electrodynamic speaker known as a so-called bail driver. It is an
object of the present invention to provide a compact speaker which enables wide-band, highefficiency reproduction with an apparent vibrating membrane area. Hereinafter, the
configuration of the present invention will be described with reference to one embodiment. FIG. 3
is a cross-sectional view of an embodiment of the present invention. The vibrating membrane 10
is formed by bending a monoball electret polymer film into an accordion pleat shape and is fixed
by a support frame 11 at both ends.
The fixed electrode group 12.13 is fixed by the support plate 14 from above and below in a form
in which it is inserted into the folds of the vibrating film from the front and back respectively.
(The top support plate is not shown in this cross section. The fixed electrode group 12 in front of
the vibrating membrane is all electrically connected, and the rear fixed electrode group 13 is
similarly wired. The upper and lower sides of the vibrating membrane 10 are adhered to the
support plate 14, and the spaces in front of and behind the vibrating membrane are completely
separated by the vibrating membrane, and there is no air leakage. The principle of operation of
this embodiment is shown in FIG. The vibrating membrane and the fixed electrode groups 12
'and 13 form a capacitor. Here, when the vibrating film is negatively electretized, positive charges
are induced on the electrodes. If there is no signal voltage, the vibrating membrane is in an
equilibrium position centered between the electrodes, as shown in FIG. 4 (α). When a signal
voltage is applied such that the front electrode group 12 is negative and the rear electrode group
13 is positive, the vibrating membrane is pushed by the electrode group 12 by the electrostatic
force and pulled by the electrode group 13. 4 As shown in FIG. As a result, the forwardly open
folds open above the equilibrium position and draw air as shown by the arrows in the figure,
while the rearward open folds close from the equilibrium position and release air. When the
phase of the signal input is reversed and the electrode group 12 is positive and the electrode
group 13 is negative, the driving force is also reverse, the diaphragm is deformed as shown in
FIG. 4 (c), and the air is released forward. Suction air from behind. When an alternating current
input is applied, the above-described motion is repeated to emit sound waves whose phases are
reversed forward and backward. Although the embodiment in which the vibrating membrane is
constituted by a monopole electret has been described above, the vibrating membrane may be
drawn by a film coated with a conductive coating, and a normal electret may be attached to a
fixed electrode. Due to the bias voltage by the electret, charge is induced on the surface of the
vibrating film, and push-pull driving is performed by the signal voltage applied to the fixed
electrode. There is almost no change except for the change of the material of the diaphragm and
the fixed electrode, and the speaker can be realized with the same configuration as shown in FIG.
In the electret electrostatic speaker according to the present invention, since the vibrating
membrane folded in accordion pleats is used as a sound source, the apparent size is the same in
size, and the electret electrostatic type having a wider area than the conventional one is used.
There is an advantage that a wide frequency band and high efficiency comparable to a speaker
can be obtained. Since the fixed electrode is not disposed at the position where the front surface
of the vibrating membrane is closed, it is not necessary to open the pore, and the manufacture is
Also, compared with the electrodynamic speaker known as a so-called bail driver, the expensive
magnetic circuit for providing a uniform bias magnetic field, which is necessary for the
electrodynamic speaker, is not required, and cost, volume and weight You can save a lot.
Furthermore, it is necessary to print a complicated electrode pattern on the vibrating membrane
surface in the case of End Page: 2 lever, but in the present invention, it is only necessary to
electretize and form a polymer film, and more. Does not require a multi-period manufacturing
process. Therefore, the formation of the vibrating film becomes very easy, and the improvement
of the yield and the cost reduction can be expected.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 and FIG. 2 do not show the operation principle of
the conventional electret electrostatic loudspeaker, FIG. 3 is a cross sectional view showing one
embodiment of the electret electrostatic loudspeaker according to the present invention, FIG. FIG.
4 shows the operation principle of the embodiment. Reference Signs List 1 monopole electret
vibrating membrane 2 front fixed electrode 3 rear fixed electrode 4 conductive coating layer 8.9
electret 10 monoball electret vibrating membrane 12 Front fixed electrode group 13 ··· Rear fixed
electrode group or more EndPage: 3
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