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Description 1, title of the invention
MFB device
3. Detailed Description of the Invention The present invention relates to an MFB (motional
feedback) apparatus, the object of which is to provide an excellent MFB apparatus capable of
expanding an acoustic reproduction band and reducing acoustic distortion. It is to do. In general,
the MFB apparatus is used to set a reproduction sound pressure from a speaker as a target sound
reproduction characteristic. 2。 This MFB apparatus is configured to control the motion of the
speaker vibration system by detecting the motion of the speaker vibration system by a detector
and returning the detection signal to the speaker drive system. A conventional MFB system is
shown in FIG. The bridge circuit is composed of a feedback circuit (referred to as a β circuit) 2
that can perform MFB operation and a resistor 3 and 4 5 speaker 6. In the h'sFβ circuit
configured in this way, the speaker speed V is generated assuming that the drive voltage is E due
to the dynamic impedance of the speaker, and the bridge circuit and the above-described
electrical impedance of the speaker are balanced. Voltage Et proportional to velocity V) = KBRv-...
(J) K: A velocity voltage detection coefficient is detected. EndPage: A voltage proportional to one
degree appears. The bridge balanced voltage obtained between A and B is subjected to
predetermined amplification by the transistor 7 and fed back to the power amplifier 1 through
the capacitor 8 and the β circuit 2 to obtain the velocity type MFB feedback. Acceleration type
feedback was obtained by having. However, although the expansion of the sound reproduction
band was made possible by the MFB acceleration type feedback of such a configuration, it was
impossible to reduce the acoustic distortion. The present invention solves such conventional
drawbacks, and the present invention will be described below with reference to the drawings of
the embodiments. FIG. 2 shows an embodiment of the MFB apparatus of the present invention,
and the same reference numerals as in FIG. 1 indicate the same constituent requirements. 2
differs from FIG. 1 in that the output of the β circuit 2 and the input signal applied to the input
terminal 9 are added to the computing unit 10 for signal processing, and the output of the
computing unit 1o and the above input signal And are added by the adder 11 and fed back to the
power amplifier 1. That is, since the acceleration voltage from the β circuit 2 is compared with
the input signal in the computing unit 10, only the nonlinear component in speed is output above
the speaker resonant frequency fO, and the input signal is output below the speaker resonant
frequency fO A low pass boost effect is obtained. The frequency characteristics of each part in
the above-described MFB apparatus are shown in FIG. 3 and FIG.
The β circuit 2 has the frequency characteristics shown in FIG. 3 because it has differential
characteristics, and the force calculator 10 subtracts the input signal from the output of the β
circuit 2 and thus in phase above the speaker resonance frequency fo At the same level, the
output of the computing unit 10 has a characteristic of being boosted below the speaker
resonance frequency fo as shown in FIG. Therefore, the output of the operation SO is added to
the input signal by the adder 11 to obtain the characteristic (low-range boost) of the acceleration
feedback, and the speaker resonance frequency f. At the above frequencies, the difference
between the input signal and the output signal of the β circuit 2, that is, only distortion of the
speaker speed voltage is mainly 5 base negative feedback, so that acoustic distortion can be
reduced. As described above, according to the present invention, it is possible to provide an MFB
apparatus with a simple configuration that expands the sound reproduction band and has a small
amount of acoustic distortion.
4. Brief description of the drawings FIG. 1 is a circuit diagram of a conventional MFB apparatus,
21 ... power amplifier, 2 ... feedback circuit, ........ Name of agent Attorney Nakao and
others 1 person Figure 1 Figure 2 EndPage: 2
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