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■ Electrostatic Speaker Referral No. 45-5424 @ 峙 [39-4357 [Phase] Application No. 39 (1964)
January 29 @ Inventor Tokohira Tai yokohama, Kohoku Ward Kono Ward, Yokohama Prefecture
880 Matsushita Telecommunications Industry Co., Ltd. Domi Do Yoshida same place 0 applicant
Matsushita Electric Industrial Co., Ltd. Kadoma city Oji Kamon 1006 [phase] agent patent
attorney Toshio Nakao 1 person outside
BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 to 6 show specific examples of the electrostatic
speaker used in the present invention, and FIG. 1 shows a variation of the effective area of the
electrode facing the diaphragm, FIG. 2 shows different electrode spacings, FIG. 3 shows
distribution of voltage to a large number of divided fixed electrodes, FIG. 4 shows changed
effective dielectric constant between electrodes, FIG. 5 shows FIG. Instead of what is shown in
FIG. 1, a number of holes are made in the fixed electrode and the effective area is changed by
changing the density of the holes, and in FIG. 6, the size of the holes is also changed. FIG. 7 is a
characteristic diagram of the conventional electrostatic speaker, FIG. 8 is a diagram showing an
embodiment of the electrostatic speaker according to the present invention, and FIG. 9 is a
characteristic diagram of FIG. FIGS. 13 and 14 show an embodiment for detecting the amplitude
of the vibrator in FIG.
Detailed Description of the Invention The present invention detects the displacement, velocity or
acceleration of a vibrating body in an electrostatic speaker and dynamically feeds it back to the
input end of a drive amplifier to control the vibration and obtain stable vibration over a wide
frequency range. The conventional electrostatic speaker which is intended to have the
characteristics shown in FIG. 7 is put to practical use mainly for high-pitched sound reproduction
[111111]. That is, since the characteristic becomes almost flat as shown in the figure at the
frequency of KA = 1 or more, only the frequency range of KA = 1 or more has been practically
used. (However, S in FIG. 1 is the effective stiffness of the vibrator, m is the substantial amount, s
/ m is its natural frequency, ffK is 2πfc, f is the frequency, C is the speed of sound, and A is the
equivalent radius. The present invention is an improvement of such an electrostatic speaker, and
as is well known, the electrostatic driving force applied to each portion of the movable electrode
or vibrating film in the electrostatic speaker is mainly on each portion on the film surface. The
vibrating membrane itself has a distribution of the driving force applied to each portion on the
vibrating membrane surface using the relative positional relationship with the corresponding
fixed electrode, that is, the driving electrode and the fact that it is determined by the potential
difference between both electrodes By making the vibration mode of free vibration displacement
correspond to or approximate to the form of the function to be changed, that is, the standard
function, it is made to vibrate in the same vibration mode over a wide frequency band, and its
vibration amplitude is detected To provide an electrostatic speaker characterized in that its
radiation characteristics are controlled by dynamic feedback to the electrostatic speaker. A
description will be given below by way of an example shown in the drawings. FIG. 1 is a crosssectional view of a circular electrostatic speaker, in which 1 is a vibrating electrode composed of
a homogeneous vibrating film, 2 is an insulator (for example, resin such as epoxy resin or phenol
resin), 3 is provided on insulator 2 And a plurality of fixed electrodes, each of which is
electrically connected and has the same potential. The fixed electrode 3 is a concentric ring, and
the width (radial direction) of the pressure electrode, which has a fixed gap each, becomes
narrower toward the periphery. Since all of these electrodes are at the same potential, when
focusing on an arbitrary point of the film, the effective area of the opposite fixed electrode is
small at the periphery and large at the center. As is well known, the reference function of the
circular vibrating membrane is proportional to the Bessel function of the first kind and is Jo (ctl-)
in a simple form. However, α1 = 2.405, r: distance from center, [111111] EndPage: 1a: radius of
film. Now, since it is proportional to the effective area of the electrode facing the electrostatic
drive force, the diaphragm is driven using this electrode by approximating the effective area to Jo
(.alpha.1L). Only vibration modes which are of the function Jo (α1-) are allowed.
Therefore, within the approximate range, the distribution of vibration displacement at all
frequencies is the same, and only one proportional to the Bessel function Jo (.alpha.1-) can be
used as the vibration mode. Also, instead of distributing the conductor on the insulator, even if
the effective area is changed by distributing many dL to the conductor plate, or even if the fixed
electrode is provided with irregularities to distribute the rate of change of the capacitance, The
vibration form can be obtained, and the vibration form can be easily obtained by the
trigonometric function as described above for the rectangular as well. Furthermore, in this
vibration mode, the phase relationship on the surface of the vibrating film vibrates independently
of the frequency. Therefore, the vibration film reference frequency is completely equal to that of
a single-resonance system having a resonance frequency, and an extremely wide-band piston-like
diaphragm, which has been considered to be extremely difficult in the past, can be realized with
equal constraints. There is also an embodiment as shown in FIGS. 2 to 4 as a method of
distributing the driving force. That is, FIG. 2 shows a conductor in which the electrode gap is
formed so that the fixed electrode 3 has a force coefficient distributed in the form of JO (ctIL),
and FIG. 3 shows one in which a DC voltage E is distributed to the divided electrodes 3. In
addition, holes 5L 52, 53 having different densities or diameters of the holes 4 provided in the
fixed electrode 3 as shown in FIGS. It is possible to give the same effect as that described above
by distributing. In FIG. 3, R is a resistive divider. As described above, according to the present
invention, the driving force distribution neglecting the vibration characteristic of the vibrator as
in the prior art, for example, the drawbacks such as uniform driving all over the surface or
driving of concentrated points A so-called divided vibration or high-order vibration does not
occur to cause unevenness on the frequency characteristics, so that an extremely monotonous
electroacoustic transducer having characteristics as shown in FIG. 7 can be realized. The above
description relates to the structure of the speaker itself that is a part of the present invention,
and may be completed by configuring the system described below as one component of the
present invention or more. The present invention will now be described by way of an
embodiment shown in the drawings. FIG. 8 is a principle view thereof, and 1 is a circular
vibrating body consisting of a vibrating electrode or a vibrating film and the periphery of the
vibrating film 10 is fixed by a fixing frame 3 There is. Reference numeral 2 denotes a vibrating
electrode, which collectively describes those having the characteristics described above, and
drives the vibrating body 1 by the output of the drive amplifier 7 obtained by amplifying the DC
power supply 9 and the AC signal 8. A detection electrode 4 is provided in the vicinity of the
vibrating membrane 1 so that the vibration amplitude of the vibrating membrane 1 can be
Reference numeral 6 denotes a feedback amount setting circuit, which amplifies the output from
the detection electrode 4 by the amplifier 6 and then adds it to the drive amplifier 7. Further,
since the drive amplifier 7 is also driven by the AC input signal 8, a dynamic feedback is
constituted as a whole, and this feedback amount is appropriately set according to the
characteristics of the vibrating body 1. As shown in FIG. 9, an electrostatic speaker which can be
used over a very flat wide band can be obtained. This is in the same form as dynamic feedback
that is generally performed in the past, but as a drawback of the conventional case, the dynamic
feedback is limited to only a very limited bass range, for example, 300 Hz or less, because the
vibration mode of the diaphragm differs depending on the drive frequency. In the present
invention, as described above, the range of dynamic feedback is extended to, for example, about
3000 Hz because the vibration mode is the same at all frequencies as described above, and the
characteristic of the feedback system is high. A speaker with excellent stability, low distortion,
etc. is realized. The detection can be easily obtained by applying the method shown in FIGS. 10 to
13 to the detection of the amplitude of the vibrator 1 in FIG. That is, in FIG. 10, the detection
electrode 4 is provided around the drive electrode 20, and as one of the features of the present
invention, this portion is detected by utilizing the fact that the peripheral portion of the
diaphragm does not give a driving force. 11 uses the detection electrode 4 inserted in the hole of
the drive electrode 2 provided with a plurality of holes 13, and FIG. 12 shows the piezoelectric
material or the piezoelectric material in the periphery of the vibrator 1 12 detects a change in
film tension corresponding to the vibration amplitude, and FIG. 13 shows an amplitude
modulation using the high frequency power supply 15 using the change in electrostatic
capacitance between the vibrator 1 and the drive electrode 2 Alternatively, the high frequency
power supply 15 is frequency modulated by the change of the electrostatic capacity between the
vibrating body 1 and the drive electrode 2 by phase modulation. EndPage: 2 The amplitude
detected by each of these methods is amplified by the amplifier 5 and applied to the drive pulse
width I through the feedback amount setting circuit 6. (However, in FIG. 8 and FIG. 10, 10 is a DC
blocking capacitor, 11 is a protection resistor, 14 is a resonant coil, 16 is a high frequency cold
ring, 17 is a rectifier, and 18 is a low frequency blocking capacitor. As described above,
according to the present invention, unlike the general electrostatic speaker having the
characteristics as shown in FIG. 7, since the vibration mode of the vibrating body is constant
regardless of the frequency, high-order divided vibration There is no instability, etc., and by
applying appropriate dynamic feedback, as shown in FIG. 9, it is possible to reproduce the
characteristics extremely flat and always stable over a wide band.