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BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
electroacoustic transducer which directly inputs a PCM (pulse code modulation 1Pl) signal and
converts it into an analog acoustic signal. [Prior Art] As a conversion system of the abovementioned electroacoustic transducer, there are an electrodynamic type, an electrostatic type, a
piezoelectric type, an electromagnetic type and the like. In addition, as a method of driving the
entire converter, (1) using a plurality of units having the same performance and driving by a
weighted PCM signal, (2) changing the area of the driving force and the diaphragm to convert the
converter itself (3) above (11, (a combination of 21 and the like). 1 and 2 show rTHE BELL
SYSTEM Science ECHNICAL JOURNAL. Novjmber 1980. It is an electrostatic type four-focus
converter using electrets and foils as the diaphragms described in pages 1693 to 1719 J, and the
driving method is the method according to the above (21) method. FIG. 1 is a front view, and FIG.
2 is a cross-sectional view. In each drawing, 1 is a disk-shaped diaphragm made of electret foil, 2
is acoustically transparent and fixed the diaphragm 1 “protrusion 2a, 2b , 2c fixed plate, 3a.
Reference numerals 3b and 3c denote ring-shaped or circular electrodes arranged concentrically,
which are fixed to and held by the insulating material 4 as a holding member, and the
protrusions 4a of the insulating material 4. It is divided by 4b and 4c respectively. The insulating
material 4 provided with the diaphragm 1, the fixed plate 2 and the electrodes 3a, 3b and 3c is
accommodated in a fixed ring 5, and an acoustic low pass filter 6 is provided on the front surface.
The diaphragm 1 has the protrusions 2 a, 2 b, 2 c of the fixed plate 2 and the protrusions 4 a, 4 b
of the insulating material 4. There are fixed parts 7a, 7b, 7c supported by 4c, whereby the
diaphragm 1 is divided into la, lb, Ic. Here, diaphragm 1a, lb. Weighting is performed by setting
the mutual area ratio of 1c to 2. A digital signal is applied to the electrodes 3a, 3b and 3c
through the input terminals 8a, 8b and 8c, respectively, but the most significant bit (MSB) of the
digital signal is switched to 10E or -E by the polarity switching switch 9. Each input terminal 8a.
The lower three focusses are sequentially applied to the input terminals 8a, 8b and 8c. The
electro-acoustic transducer has diaphragms 1a, 1b and 1c, electrodes 3a, 3b and 3c facing them,
and input terminals 8a, 8b and 8c, respectively. Each unit 10a comprises 10b, 10c.
One electroacoustic transducer is composed of 10b and '10c. In such a configuration, when a
PCM signal is applied to the units 10a, 10b, and IOc corresponding to each bit, a pulse amplitude
modulated sound pressure is generated from the converter. In the multi-unit converter system as
described above, the individual units lOa that constitute it. 10b, IOC must simultaneously
generate sound pressure proportional to the area. The individual units 10a, which ignore the
level differences corresponding to the area. It is desirable that the output sound pressure
frequency characteristics (hereinafter referred to as f characteristics) of 10b and 10c be the
same. However, in the transducer in which the diaphragm 1 is fixed concentrically as in the
conventional example, the divided diaphragms la, lb, and lc have different shapes and areas,
respectively, so each unison 10a, 1 ( lb. The trends for the 10C f characteristic are different. Next,
the characteristic tendency will be described with reference to FIGS. 3 (a) to 3 (i). The same
figure (al shows a time waveform (impulse) of an input signal, (bl-(dl and (f)-(hl is a time
waveform of an output sound pressure when each unit is driven independently (impulse
response), (E) and (i) also show the f characteristic. The figure (bl-(C) shows the characteristic of
an ideal electroacoustic transducing unit, (f)-(il shows the characteristic of the actual unit like the
above-mentioned conventional example). Represents time, F represents frequency, and the
vertical axis represents i bell and La represents sound pressure level. Also, A, AI, B, and Bt
represent the respective characteristics, and subscripts a, b, and c represent the uniso of the
conventional example) 10a. It corresponds to 10b and 10c. If each unit is ideal, as shown in FIG.
3 cby to (d), impulse response waveforms Aa, Ab, Ac similar to the input signal shown in FIG. The
amplitude of the (sound pressure level La) changes by double. In order to obtain such a
waveform, as shown in FIG. 6E, the f-characteristics Ba, Bb and Bc of each unit must have a
constant level difference of 6 dB over the entire frequency band. However, the unit 10a shown in
the conventional example. The f characteristics of 10b and 10c have a tendency as shown in FIG.
3 (11. This is a fixed part in which each diaphragm 1a, lb, lc is fixed by the projections 2a, 2b, 2c
and the projections 4a, 4b, 4c? Because the 'a, 7b, 7G are included, the reproduction band of low
and high frequencies is limited. The smaller the area of the diaphragm is, the more the
reproduction band is shifted to the higher frequency, the higher the frequency. In the region,
resonance between the diaphragms occurs and the sound pressure level La fluctuates, and the
central diaphragm IC and the diaphragm 1a outside the central diaphragm IC.
The fixed condition is different at lb and so on. For this purpose, the impulse response waveform
changes as shown by Ala, Alb, and Ale in FIG. 3 (f) to Th), and a regular sound pressure level can
not be obtained by continuing small level fluctuations, and as a result, The f characteristic can
not maintain the level difference of 6 dB at low frequency and high frequency as shown in FIG. 3
(il. SUMMARY OF THE INVENTION According to the present invention, a holding member for
holding an electrode is provided with a holding frame for holding the outer peripheral side of a
diaphragm, and only the outer periphery of the diaphragm is held by the holding frame to
remove the above defects. This will be described in detail with reference to the following
examples. FIG. 4 is a cross-sectional view showing an embodiment of the electroacoustic
transducer according to the present invention. The same reference numerals as in FIG. 2 denote
the same parts in FIG. In the figure, the electrodes 3a, 3b and 3c are held by being fitted to the
concave portions 11a, 11b and 11c provided on the surface of the insulating material 11 as a
holding member corresponding to the shapes of the electrodes 3a, 3b and 3c. The insulating
portions 12 of the insulating material 11 insulate each other. On the other hand, the diaphragm
1 is disposed to face the electrodes 3a, 3b and '3c, and only the outer periphery is fixed and held
by a holding frame 13 provided so as to project from the outer periphery of the insulating
material 11 to the front. As described above, in the present embodiment, the fixing plate 2 having
the protrusions 2a, 2b and 2c in the conventional example and the protrusions 4a, 4b and 4c of
the insulating material 4 are not provided, and the fixing portion? A, 7b and 7c are eliminated
and the diaphragm 1 is held only by the holding frame 13. Vibration is given to each portion of
the diaphragm 1 corresponding to each of the electrodes 3a, 3b and 3c. Vibrates as a sum. As a
result, the f characteristic of each unit of the converter is as shown in FIG. 5, and a
predetermined level difference can be maintained over the entire band. For this reason, a regular
reproduced sound can be obtained in almost the entire frequency band. In the above
embodiment, the vibration + 7i 1 and the electrode 3 are circular, and the electrode 3 is
described as an area proportional ring, but the invention is not limited thereto. For example, a
square diaphragm is used. In addition, as shown in FIG. 6, an area proportional electrode 3
divided by the insulating portion 12 may be provided, or a circular or rectangular diaphragm
may be used in FIG. 6 (al, (ins as shown in bl The electrodes 3 divided into equal areas by the
part 12 may be provided, and the driving method described in the beginning of the description
may be adopted. Further, although the electrostatic type converter has been described in the
above embodiment, a diaphragm of a film type such as a piezoelectric type may be used.
By the way, in the above description, an electro-acoustic transducer has been described in which
a PCM signal is directly input and converted into an analog acoustic signal. It goes without saying
that it can be applied to the speakers of the way speaker device. As described above, according to
the electro-acoustic transducer of the present invention, the holding member for holding the
electrode is provided with a holding frame for holding the outer peripheral side of the
diaphragm, and the outer periphery of the diaphragm is held by the holding frame. Since only the
sound is held, a good reproduced sound can be obtained.
Brief description of the drawings
1 and 2 are a front view and a sectional view showing an example of a conventional electroacoustic transducer, FIG. 3 is a characteristic diagram for explaining the operation of the
conventional example, and FIG. 4 is an embodiment of the present invention. FIG. 5 is a crosssectional view showing an example, FIG. 5 is a characteristic view showing the operation of the
above embodiment, and FIG. 6 and FIG. 7 are configuration diagrams of electrodes showing
another embodiment of the present invention.
DESCRIPTION OF SYMBOLS 1 ... Diaphragm, 3 ... electrode, 11 ... insulation material, 12 ...
insulation part, 13 ... holding frame. The same reference numerals are used for the same or
corresponding parts in the drawings. Agent Ms. Oiwa, a (2 other persons) Fig. 4 Fig. 5 Fig. 6 Fig.
7 Procedure amendment (self-represented '3 10 A6 Secretary General of Japan Patent Office 1,
indication of the case No. 099-976 2, title of the invention electro-acoustic transducer 3,
representative of the person making corrections Hitoshi Katayama Part 5, column of detailed
description of the invention subject to correction. 6. Correction contents + 11 The specification
“Page 6 of the specification, line 5“ Resonance between plates ”is corrected to“ resonance of
grid ”. that's all
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