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DESCRIPTION OF THE PREFERRED EMBODIMENTS Electroacoustic Transducer 1. A first
diaphragm electrically driven, an air spring coupled to the first mobile plate with an airtight
space, and a second diaphragm in contact with the air. And, an electrical sound etc. converter
composed of an air chamber and a resonator whose crotch is made of nine sound release ports in
the air chamber.
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the broadening of
an electroacoustic transducer. Although electro-acoustic transducers used as sound sources for
small portable devices such as watches and pagers generally use resonance due to power
consumption limitations, those using resonance can not obtain enough bandwidth. There is a
drawback of that. The present invention seeks to achieve a wide bandage while utilizing
resonance. Specifically, the conventional electroacoustic transducer has one degree of freedom of
the mechanical vibration system, and thus has only one mechanical resonant frequency, whereas
the acoustic transducer of the present invention has a mechanical frequency of one. A vibration
system with two degrees of freedom, two mechanical resonance frequencies, an acoustic effect
between the second mechanical resonance frequencies, and a constant sound pressure, thereby
broadening the bandwidth It is. This will be described below with reference to the drawings. FIG.
1 is a cross-sectional view showing the structure of the conventional example, 1 is a coil with a
center ball core 2 made of soft magnetic material, 3 is a magnet, 4 is a support, 5 is a diaphragm,
6 is a diaphragm 5 It is a yoke made of a fixed soft magnetic material. In this acoustic transducer,
when alternating current is supplied to the coil 2, a force of attraction or repulsion acts on the
yoke 6 from K, and the force causes the diaphragm 5EndPage: 1 to vibrate and generate sound.
Although it occurs, the vibration system basically has one degree of freedom and The sound
pressure-drive frequency characteristic is as shown in FIG. 2, which has one resonance point 9
and the frequency band .DELTA.f1 which can obtain more than the constant sound pressure Po
shown in FIG. FIG. 3 is a cross-sectional view showing the structure of another conventional
example in which the narrow frequency band is improved. Those indicated by numerals 1 to 6
are the same as in FIG. The new one is an acoustic gore indicated by 7, 7α is a sound emission
hole provided in the acoustic case 7, and 8 is a space constituted by the acoustic case 7 and the
diaphragm 5. Such a configuration is shown in FIG. 4 by making the diaphragm resonance
frequency close to the Helmholtz's resonance frequency by an appropriate design because a socalled Helmholtz's resonator is produced by the sound emission lower G and the space 8. Such
sound pressure-driving frequency characteristics can be obtained, and the band Δf more than
the constant sound pressure PO can be considerably improved over the eight f1 obtained in the
structure of FIG. In applications where one drive frequency is used, if electroacoustic conversion
of the structure shown in FIG. 3 requires sounds different by 1/2 to 1 octave, it is no longer
possible to meet the requirements sufficiently with this structure. It's done.
An object of the present invention is to provide a wide-band electroacoustic transducer that can
meet such a demand, and will be described below with reference to the drawings. FIG. 5 is a view
for explaining the present invention, and is a cross-sectional view showing a structure of a
mechanical vibration system in which the degree of freedom of the mechanical vibration system
is 2. 1 showing the conventional example and those shown by the numerals 1 to 6 are the same,
but the fundamentally different point is that they are electromagnetically driven and opposed to
the diaphragm 5 with the yoke iron 6. The provision of the second diaphragm 9 is important. The
diaphragm 5 and the second diaphragm 9 are air-spring coupled with an air-tight space 9. In the
electro-acoustic transducer having such a configuration, the diaphragm 5 with the yoke 6 is
electromagnetically driven by supplying an alternating current to the coil 2, but no sound is
generated from the diaphragm 5, and the space 10 is airtight. By the vibration of the second
diaphragm 9 coupled by the air spring according to The sound pressure-drive frequency
characteristics of the electroacoustic transducer having such a structure are as shown in FIG. 6 or
have two resonance points. The sound pressure-drive frequency characteristics of the present
invention will be described with reference to FIGS. 7 and 8 below. If the vibration system in the
structure of FIG. 5 is isometrically rewritten, it can be written as shown in FIG. Here, M, ZM
respectively represent the equivalent mass, equivalent spring coefficient, and amplitude of
diaphragm 5 with yoke 6 in FIG. 5, and m, ztn respectively represent the second diaphragm 90 of
FIG. Equivalent mass, equivalent spring coefficient. The amplitude is represented and ka
represents the air spring constant of the space 10 in FIG. The above are the main vibration
system components, and in fact they are damping resistances. The acoustic impedance must be
honored, but it was omitted to simplify the explanation. The forced vibration solution when the
alternating force X 'sinmt is added to the mass M of the vibration system is expressed by the
following equation. As can be seen from the equation of (10 or more), as shown in FIG. 8, two
resonance points appear, and their amplitude-drive frequency characteristics can be represented
as shown in FIG. If attention is paid to the amplitude yernjfc of the diaphragm 9 from FIG. 8 to
FIG. 6, it will be apparent that the sound pressure of FIG. 6 can be obtained. Properly selecting
the constants of the vibration system shown in FIG. Therefore, the resonance frequencies f and f
shown in FIG. 8 can be made close to each other, but they can not be perfectly matched unless
constant = 0, and there are always two resonance points. Come out. At the two resonance points
of such a vibration system, the sound pressure becomes quite large, but in terms of band, Δf 88.
Δ f8. The degree is usually not usable and not sufficient.
What is intended to compensate for this by sound effects and to make the band sufficiently wide
will be described in the main point of the present invention by 1) FIG. EndPage: 2 FIG. 9 is a
cross-sectional view of the structure of the acoustic transducer showing one embodiment of the
present invention. Basically, the youth case 7 is provided in FIG. 5, and those indicated by
numerals in the figure are the same as those described above. In the acoustic transducer to be
aware of such a structure, if the Helmholtz resonance frequency is set to the middle of the
mechanical resonance frequency f and fl of the second diaphragm described in FIG. 8, the sound
pressure shown in FIG. As shown in the figure, the drive frequency characteristic becomes a wide
band as shown in FIG. In the above description, the electro-mechanical conversion has been
described using an electromagnetic type, but it is apparent that the same effect can be obtained
using other electro-mechanical transducers such as a piezoelectric type or an electrodynamic
type. It is. In the past, a thin b plastic film or the like was attached to the same place, which
corresponds to the second diaphragm 9 of the present invention, mainly for the purpose of
moisture resistance, dust resistance, etc. The purpose of the invention is distinctly different, and
the effect on the vibration system is equivalent to almost zero, and the idea for broadening the
bandwidth of the present invention is distinctly different. Although the example has been
described using a Helmholtz resonator as the resonator, the present invention is not limited to
this, and any resonator can be used as long as it is a resonator composed of an air chamber and a
sound emission port. As described above, the electro-acoustic transducer according to the
present invention uses resonance actively and can obtain wide band tones, so it can provide
various timbres with low power consumption, and can be used in watches and pockets. The effect
is remarkable because it greatly contributes to the multifunctionalization of small portable
devices such as Bell.
Brief description of the drawings
1 and 3 are sectional views showing the structure of the conventional example, FIG. 5 is a
sectional view showing the structure of the main part for explaining the present invention in
detail, and FIG. 7 is a simplified vibration system of the present invention. The figure is shown in
FIG. 9 is a cross-sectional view of a structure showing an embodiment of the present invention. 2,
4, 6, 8 and 10 are diagrams showing drive frequency characteristics. 1.0. Magnetic core
with center ball 20. . コイル300. Magnet 4 °,. Support 5 °. . Vibrating plate 600. Bare iron
7. . , Acoustic case 8 ° 0. Space 9 ° 0. Second diaphragm 1o0. . space. Above-", Agent Best
Practice EndPage: 3
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