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Description 1, title of the invention
Small speaker
3. Detailed Description of the Invention The present invention relates to a small speaker for low
power, and more particularly to a small speaker suitable for portable electronic devices. Smallsized speakers used in portable radios, etc., which are operated by conventional batteries, are
limited to electrokinetic cone speakers. Electromagnetic cone speakers often used at the
beginning of radios are inexpensive and have good sensitivity, but their displacement amplitude
is small. It is not used at present because of the disadvantage that nonlinear distortion is large
and the resonance frequency can not be lowered. The sound output of such a small loudspeaker
is, as is well known, proportional to the fourth power of the radius at a low frequency, and
therefore drops sharply at a small aperture. In addition, the mass of the vibration system
becomes smaller than the mass of the driving system of the amateur or voice coil, and the fit
becomes worse. In addition, the efficiency is further reduced because sufficient magnetic flux can
not be obtained in the air gap of the magnetic pole due to miniaturization. For this reason, in the
electrodynamic type, the efficiency does not reach 1 percent, and therefore, a power of about one
hundred milliwatts is required, which is larger than the current consumed by the electronic
circuit other than the speaker, which affects the battery capacity. SUMMARY OF THE INVENTION
The present invention is to provide a small power small speaker which improves the efficiency by
butterfly vibration replacing the piston vibration of the conventional cone speaker and eliminates
the above-mentioned drawbacks of the electromagnetic type.
Small speaker
Hereinafter, the present invention will be described in detail by way of illustrated embodiments.
One embodiment of the small speaker 1 is shown in FIG. In this small speaker l, a permanent
magnet 3 in the center of the frame 2. The EndPage: 1 cylindrical outer pole 4 at its lower end
and the disc shaped inner pole 5 at its upper end, and a ring-shaped air gap 6 is formed between
the two to obtain the required space. Supply DC flux. A coil 7 is wound around the outer
periphery of the permanent magnet 3. A diaphragm 9 is placed on the upper surface of the inner
pole 5 via a spacer 8, and the through holes of the spacer 8, the permanent magnet 3 and the
frame 2 are caulked through the rivet 11 in the central through hole 10 thereof. The diaphragm
9 is made of a thin metal plate having a large specific elastic modulus, and a crimp having the
same diameter as that of the spacer 8 is formed at the center thereof to form a fixed circle 12.
The drive 14 is formed by pleating at a position at which the inside and the free end 13 are
internally divided at a suitable lever ratio, and the ring-shaped armature 15 is fitted and fixed
thereto. The armature 15 arranges the fold 17 as shown in FIG. 2 between the 0 drive circle 14
and the free end 13 where the suction is carried out by sucking the slit 16 into the air gap 6. . In
addition, a gap 18 is provided between the free end 13 and the frame 2. Next, the operation
principle of the small speaker will be described. FIG. 3A shows piston oscillation by a
conventional cone-shaped diaphragm in dotted lines, and FIG. 3B shows butterfly oscillation by
the center fixed and peripheral free diaphragm of the present invention. The same amplitude is
given for driving as shown by both arrows, and the volume change amount of the space serving
as an indicator of the sound output is compared. Now, assuming that the loss of the peripheral
support portion of the piston vibration and the loss of the central fixed portion of the butterfly
vibration are equal, in the butterfly vibration, the drive ratio 14 for the lever ratio, ie the distance
between the fixed circle 12 and the drive 14 and the free end 13 When the interval ratio with is
larger than 1, it can be easily calculated that the volume change amount is larger than the piston
vibration, and when the lever ratio is 2, it is approximately doubled. In this case, at the same
time, the mass of the vibration system seen from the drive 14 can also be increased by the lever
ratio, but if the mass of the drive system is large as described above, the lever ratio can be
increased to increase the acoustic output to improve the efficiency. However, since the butterfly
vibration is at the free end 13, the forward sound pressure can be eliminated by the antiphase
sound pressure from the rear, so a gap 18 is provided between the free end 13 and the frame 2
to suppress this. At the same time, the diaphragm 9 is damped. A damper ring made of an elastic
member may be provided between the weir, the free end 13 and the lower frame 2.
In addition to the above, the lowest resonance frequency that can be taken by the vibration
system is a problem, but in the case of butterfly vibration, it is shown by the formula for
mechanical vibration that it can be designed sufficiently low even with a small diameter. Further,
since the drive 14 is in the vicinity of the fixed circle 12, the stiffness is large, and there is an
advantage that the positional accuracy can be stabilized. Next, the electromagnetic converter 19
of the present invention will be described. The driving force generated in the armature 15
coupled to the diaphragm 9 works in the magnetic circuit The squared term of the sum of the
magnetomotive force of the permanent magnet 3 and the magnetomotive force by the signal
current of the coil 7 And the change ratio of the permeance, and as is known, it comprises the
following three terms. The first term is the attraction force by the direct current magnetic flux
passing through the armature 15 in the air gap 6 by the permanent magnet 3 and is substantially
constant with respect to the displacement if the leakage flux is neglected. The design values of
the permanent magnet 3 and the like are determined such that the tip of the armature 15 is in
the middle of the depth of the air gap 6 at a position where this suction force and the restostatic
force of the vibrator 9 in the armature 15 are balanced. The second term is the same effective
driving force as the signal current of the coil 7, preferably in proportion to the DC magnetic flux
density, and as narrow as possible the gap 16 in order to increase the change ratio of permeance.
The third term is caused only by the signal current, and is composed of a double frequency
component and a direct current component to become harmonic distortion, but can be made
sufficiently smaller than the second term. In the conventional electromagnetic transducer, since
the armature is attracted to the pole face through the air gap, sensitivity increases sharply when
the displacement amplitude is increased, and the attractive force increases in inverse proportion
to the square of the air gap width, so non-linear It is a factor of distortion and instability. In this
mechanism, the displacement amplitude can be increased by the thickness of the inner pole 5
without these drawbacks. In the above embodiment, the butterfly vibration of the present
invention and the electromagnetic converter 19 are combined to take advantage of their features,
but as shown in FIG. 4, the voice of the butterfly diaphragm and the electrodynamic converter 20
is used. By combining the coil 21, (6) EndPage: 2 can also be expected to improve efficiency and
other advantages. Of course, the present electromagnetic converter can be applied to other
diaphragm drive systems. According to the present invention, as mentioned above, the
introduction of butterfly vibration instead of conventional piston vibration is advantageous for
reducing the drive amplitude to improve the acoustic efficiency of the small aperture diaphragm
and to obtain the required acoustic output. is there. In addition, a large displacement amplitude
with linearity can be obtained by this electromagnetic transducer. By connecting directly to the
small power transistor and adding the current sensitivity gain by impedance, a small speaker
operating at several milliwatts can be realized.
4. Brief description of the drawings. FIG. 1 is a cross-sectional view of a small speaker, FIG. 2 is a
plan view of the small speaker, FIG. 3 is a principle view of conventional piston vibration and
butterfly vibration of the present invention, and FIG. It is sectional drawing of the small speaker
which couple | bonded the electrographic converter. ■ ■ · · · small speaker, 2 · · · frame, 4 · · ·
cylindrical outer pole, 5 · · · disk inner pole, 6 · · · · · · · · · · · · · · · · · fixed Circle, 13 · · · Free end, 14 ·
· · For driving, 15 · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · applicant
applicant Masao Sakurai EndPage: 3 procedural corrections April 2r 1 r Case 1 Display of the
patent application No. 130,217 patent application No. 130,217 small speaker 3 person who
makes correction 4, date of correction instruction (spontaneous) 5 object of correction
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