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BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of a conventional
electrodynamic speaker. FIG. 2 is a cross-sectional view of the electrodynamic speaker according
to the present invention, and FIG. 3 is a cross-sectional view of another embodiment of the
present invention. 1: Magnet, 2: Center pole, 3: Yoke, 4: Magnetic gap, 5: Diaphragm, 6: Voice
coil, 7: Frame, 8a, b: Front, rear diaphragm, 9: Voice coil, 10: Bobbin , Lla, b: front and back
magnets, 12: center pole, 13: side yokes, 14a, b: front and back yoke plates, 15: sound emission
holes, 16: annular magnets, 17: center poles.
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the improvement
of electrodynamically driven speakers. Conventionally, as shown in FIG. 1, the electrodynamic
drive type speaker is composed of a magnet 1, a center pole 2 and a yoke 3 and a voice coil 6
fixed to a diaphragm 5 enters a magnetic gap 4 of a permanent magnet circuit. The structure has
a structure in which a diaphragm or a driving force is obtained by an audio signal input to a coil.
In the figure, 7 is a frame. In the speaker of such structure, the sound pressure is mainly obtained
from the sound wave radiated from the front surface of the diaphragm from 1-1), the sound
output radiated from the rear surface is infinite baffle, closed baffle, bass reflex, etc. In the
construction of the magnetic circuit, it is necessary to enlarge the size of the magnet to realize
high efficiency, and it is disadvantageous from the economical aspect as well as the shape aspect.
It is. The present invention improves the conventional speaker having the above-mentioned
drawbacks, and for example, by mounting it on a thin microteleco, a radio, etc., the difference in
the acoustic output from the front and back can be left It aims at providing a thin speaker with
high efficiency. An embodiment of the present invention will be described below with reference
to the drawings. In FIG. 2, 8α and 8h denote a front diaphragm and a rear diaphragm, both of
which are connected by a bobbin 10 wound with a voice coil 9, The shape is flat and annular.
1111.1116 are disposed with the same poles facing each other via a recenter ball 12 which is a
front magnet and a rear magnet. The reference numeral 13 denotes a side yoke, and 14a and 14
& are a front yoke plate and a rear yoke plate each having a sound output hole 15. In such a
structure, 2-) the driving force of the voice coil is equally transmitted to the front and rear
diaphragms, and hence the absolute values of the acoustic outputs radiated from the front and
rear sound emission holes become equal. In this case, it is also possible to create an acoustic
resonance space between the diaphragm and the yoke plate by appropriately selecting the size
and number of sound emission holes, which means that the frequency to be lifted can be freely
selected. Can also be a high cut filter. The magnetic circuit may be one using two cylindrical
magnets as shown in FIG. 2 or one using an annular magnet magnetized in the radial direction as
shown in FIG. Go through the direction. Here, 1h in FIG. 3 is an annular magnet, and 17 is a
center pole. In either case, it is also conceivable to open the sound emission hole in the side yoke
to determine the acoustic resonance point mentioned above and to obtain an appropriate
resonance frequency, and to realize the thinning, a high energy product magnet Are necessary,
and rare earth magnets are most appropriate.
As described above, according to the present invention, two diaphragms are used to radiate
sound waves to the front and rear surfaces -C. Since the pressure is obtained and the
configuration of the magnetic circuit is complete, the efficiency is improved without becoming