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■ Push-pull type capacitor acoustic converter O Patent Application No. 45-324380 Application
No. 45 (1970) April 14 @ Inventor's location Borrowing gate True type Large letter Kadoshin
1006 Matsushita Electric Industrial Co., Ltd. Takahisa Aoi Co., Ltd. 出 願 Applicant Matsushita
Electric Appliances and Industry Co., Ltd. Kadoma City Oji Kadoma 1006 [Fa] Agent Attorney
Oshima-One public person
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory view of the principle of a
transformerless push-pull capacitor speaker shown as an embodiment of the push-pull capacitor
acoustic converter of the present invention. FIG. 2 is an explanatory view showing a conventional
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a push-pull type
capacitor acoustic converter such as a capacitor speaker, a microphone, a pickup, etc., and its
object is to eliminate the need for a high voltage DC bias power supply, to stabilize the sensitivity,
and to conduct the conductive layer. It is an object of the present invention to provide a highquality push-pull type capacitor acoustic transducer by preventing a short circuit between the
fixed pole and the fixed pole. The basic model of a conventional push-pull capacitor speaker is
shown in FIG. 2. The vibrating film 1 having a conductive layer 2 on one side of which aluminum,
silver or the like is vapor-deposited is made of highly insulating plastic such as mylar, nylon or
vinyl. A back fixed electrode 4 made of a material and provided with a large number of small
holes 5 is provided on both sides of the vibrating membrane 10 through narrow air layers 6, 6
necessary for acoustic performance. 7.7 are spacers of appropriate thickness so that the air
layers 6, 6 can be formed, and 8 is a metal fitting or device for sandwiching these from both
sides. Now, a human power signal e is superimposed on a direct current high-voltage power
supply Eo of several hundred volts via push-pin [111111] terminal transformer T and applied to
this speaker to vibrate the diaphragm with its electrostatic force to produce sound. . However, in
such a configuration, a DC power supply of several hundreds of volts is required, and the
ionization phenomenon of the air layer due to the DC bias causes instability in sensitivity or high
pressure is applied, resulting in a danger in handling. There were some difficulties such as one.
The present invention is structurally the same as in the prior art, but the two thin film electrets
(electret) have their surface charges of the same polarity and the same sign as each other, or they
are bonded or crimped. It is characterized in that it uses a film, and its configuration will be
described below according to the drawings shown as the embodiments. The example shown in
FIG. 1 does not use a push-pull transformer, and the transformer T shown by a dotted line is a
simple impedance matching transformer. In FIG. 1, reference numeral 1 denotes a vibrating film
of an electret made of a plastic film such as tetron, vinyl, nylon or the like, and 3 denotes a joint
portion of the same sign and the same direction of polarity. Reference numerals 4 and 4 denote
back fixed electrodes having a large number of small holes 5, and 6 and 6 denote air layers
provided between the vibrating membrane 1 and the back fixed electrodes 4 for improving
acoustic performance. If the same sign of the polarity of the two electret films is pasted together
to form the vibrating film 1, 1, and the surfaces in contact with the air layers 6, 6 have the same
sign, the air generated by the permanent surface charge σO of the electret The electrostatic
fields Eo in the layers 6, 6 point in opposite directions as shown.
If an alternating current electric field Ei is supplied to the direct current electric field Eo as
shown in the figure, the electric field weakens in the upper air layer 6, and the vibrating films 1,
1 recoil from the back fixed electrode. On the other hand, in the lower air layer 6, the electric
field is in the same direction, so the vibration film 1, 1 is attracted to the back fixed electrode 4.
Therefore, from [111111] EndPage: 1 in which the force received by the electric field in the air
layer is in the same direction with respect to the vibrating membrane, the vibrating membrane
reciprocates in accordance with the AC signal. That is, in the upper air layer 6, EO and Ei have
opposite phases and the attraction is weakened, and in the lower air layer 6, Eo and Ei are in
phase, the attraction is intensified, and the diaphragm moves downward. At the moment of the
alternating electric field Ei, it is opposite to this and moves upward. The sound waves emitted by
the reciprocating motion of such a vibrating membrane are emitted to both sides through the
small holes 5 and become speakers. Although the thickness t of the vibrating film 1 ° 1 of the
electret is the same and the gap d of the air layers 6, 6 is the same for convenience of
explanation, the operation principle is not different even if they are different. . Working Example
Diaphragm diameter 605 jl! 71! Thickness (15 μ + 15 μ), d = 20 μ Tetron film, electret
consisting of about 98 dB (on axis 50 (177 L) equivalent to human power IW. A sound pressure
of 5 KC was obtained. Since the theoretical output sound pressure IP + of the electret speaker is
50 (1771, in the mass control region, the push-pull type capacitor acoustic converter of the
present invention is configured as described above, a high voltage DC bias power supply is
unnecessary. Because of this, there is no instability in sensitivity due to ionization in the air
layers 6, 6, and there is no danger or restriction on the body in use. Since the speaker does not
require a bias power supply terminal as in the prior art, lead extraction is easy and cost is low.
The vibrating membrane is an electret made of a highly insulating plastic film. The construction
of the present invention results in low manufacturing costs which do not necessarily have to be
vapor deposited when electretizing a film. Furthermore, since it is a push-pull type, distortion is
low (and because the attraction force by the DC electric field in the air layers 6, 6 is balanced, the
reproduction lower limit frequency can be lowered compared to a single type) There are
characteristic effects such as being obtained.
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