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DESCRIPTION JPS58103292

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DESCRIPTION JPS58103292
[0001]
The present invention relates to an MFB speaker configured to detect vibration displacement of a
diaphragm as an electrical signal and apply the detected signal as a negative feedback signal to a
driving amplifier for the diaphragm, the purpose of which is the vibration system. An object of
the present invention is to provide an MFB speaker capable of reducing distortion without
increasing its weight and reproducing a frequency lower than the lowest resonance frequency fO.
In general, an MFB speaker detects vibration displacement of a diaphragm as an electrical signal
and applies this electrical signal to a drive amplifier of the diaphragm as a negative feedback
signal to reduce distortion of the vibration of the loudspeaker itself. . And, in the conventional
MFB speaker, the negative feedback signal is obtained by adding a timing detector or a positive
charge type accelerometer to the vibration system. However, in this case, the weight of the
detector is added to the vibration system, so there is a disadvantage that the sound conversion
efficiency of the speaker itself is reduced, and the high frequency range reproduction limit
frequency is lowered for the high sound speaker. There was a drawback. The present invention
solves the above-mentioned conventional drawbacks and optically indirectly detects the vibration
displacement of the diaphragm and converts it into an electrical signal, and this electrical signal
is used as a negative feedback signal of the diaphragm driving amplifier. It is configured to be
added. Hereinafter, embodiments of the MFB speaker of the present invention will be described.
FIG. 1 shows an embodiment of the MFB speaker according to the present invention. In FIG. 1, 1
is a light emitting element, 2 is a light receiving element, 3 is a diaphragm surface to be a light
reflecting surface, 4 is a diaphragm, 6 Is an end, 6 is a damper, 7 is a voice coil, 8 is a voice coil
bobbin, 9 is a gold wire for a manual signal, 10 is an input terminal, 11 is a frame, 12 is a
magnetic circuit yoke, 13 is a yoke and center pole, 14 is a magnet 16 is a current source of the
light emitting element 1, 16 is an amplifier for amplifying the output signal of the light receiving
element 2, 17 is a differentiator for differentiating the output signal from the amplifier 16, and
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18 is an amplifier for driving the diaphragm 4 The output signal of the differentiator 17 is
applied to the negative phase input terminal, and the drive input signal from the input terminal
19 is applied to the in-phase input terminal. The yoke 12.13 and the magnet 14 constitute a
magnetic circuit, and a predetermined magnetic gap is provided between the outer peripheral
surface of the center pole integrated with the yoke 13 and the inner peripheral surface of the
yoke 12. The upper first diaphragm 4 is provided with a voice coil bobbin 8 in which a voice coil
7 is wound, and is supported on the frame 11 by the edge 5 and the damper 6 so that piston
movement is possible.
The voice coil 7 is disposed in the magnetic gap formed by the magnetic circuit, and a signal
obtained by amplifying the drive input signal by the amplifier 18 is applied to the voice coil 7
through the gold wire 9. Are configured to be However, the drive signal is applied to the voice
coil 7 in the magnetic gap to be converted into piston motion, and this force drives the
diaphragm 4 to perform piston motion. The light emitting element 1 and the light receiving
element 2 are disposed on the upper end plane of the center pole integrated with the yoke 13
and are disposed on the light reflecting surface 3 of the diaphragm 4 parallel to the upper end
plane of the center pole. Are facing each other. The light emitting element 1 and the light
receiving element 2 are set so that the central axis x-x 'of the diaphragm 4 is a reflection point.
The light emitted from the light emitting element 1 is reflected by the reflecting plate surface 3
and is incident on the light receiving element 2. The light intensity of light incident on the light
receiving element 2 differs depending on the position of the reflecting plate surface 3 according
to the vibration variation f1't of the knee diaphragm 4, and the output current of the light
receiving element 2 increases or decreases accordingly. Therefore, it is possible to obtain a signal
associated with the vibration displacement of the diaphragm 4. The electric signal of the light
receiving element 2 is applied as a negative feedback signal to the negative phase input end of
the drive amplifier 18 through the amplifier 16 and the differentiator 17. As shown in FIG. 2, the
vibration displacement detection system of the diaphragm 4 constituted by the light emitting
element 1 and the light receiving element 2 changes the distance d between the diaphragm 4 and
the light reflecting plate surface 3 as shown in FIG. It appears as a change in the output current,
whose linearity is ensured within a certain amplitude. Then, during the amplitude, it is possible to
realize both of a small amplitude and a large amplitude by selecting an element appropriately.
Although the light emitting element and the light receiving element are separately shown in the
above-described embodiment, it is needless to say that the same effect can be obtained even if
they are arranged concentrically as shown in FIG. In the above embodiment, the central portion
of the diaphragm 4 is a flat surface, which is used as the light reflecting plate surface 3. In
addition to this, as shown in FIG. 4, the dust cap 4 'is a part of the diaphragm 4. A plane 3
perpendicular to the direction of vibration may be placed on the F plane of the plate, and this
may be used as a light reflecting plane, or as shown in FIG. It goes without saying that the lower
surface of the diaphragm 4 ′ ′ may be made to be the light reflecting surface 3 directly. As
described above, according to the present invention, a light emitting element for emitting light
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toward a light reflecting surface provided on the lower surface of a diaphragm and a light
receiving element for receiving light reflected from the light reflecting surface And the vibration
displacement signal of the diaphragm detected by the light receiving element is applied as a
negative feedback signal of the drive amplifier through the arithmetic circuit, so that the speaker
vibration system is installed. By detecting this vibration and negatively feeding it back to the
drive amplifier, even the vibration system of the speaker is included in a series of feedback loops,
so that the sound emitted from the speaker also becomes less distorted.
Also, although the low resonance frequency f of the speaker alone is not reproduced, the
reproduction band can be expanded to ro or less by using the MFB speaker. Furthermore, since
the light receiving / emitting element does not add weight to the vibration system at all, light is
used for detection of the movement of the vibration system and noncontact detection is
performed, so that the weight of the vibration system is not increased. Therefore, it has the
advantage of being able to eliminate the problem of lowering the low efficiency high frequency
band 14 f raw limit frequency, which is a drawback in the conventional MFB speaker.
[0002]
Brief description of the drawings
[0003]
FIG. 1 is a cross-sectional view showing an embodiment of the MFB speaker according to the
present invention, FIG. 2 is a characteristic diagram of a light absorption vibration change λwave detection system used for the speaker, and FIG. FIG. 4 is a perspective view showing an
example of a dynamic vibration detection system, and FIGS. 4 and 5 are cross sectional views
showing another embodiment of the MFB speaker of the present invention.
1 · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · / · · · · · · · diaphragm. Name of Agent
Attorney Nakao Toshio Other 1 person Figure 1 Figure 2 Figure 2
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