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FIELD OF THE INVENTION This invention relates to audio devices. Conventionally, when
motional feedback (hereinafter referred to as “MFB”) is applied to a speaker, as shown in FIG.
1, the operation or sound output of the vibration system from the speaker 3 connected to the
power amplifier 2 is The oscillation characteristics are all detected and fed back to the input, but
the feedback amplifier 5 and the input circuit of the power amplifier 2 are complex circuits
including two points of the equalizer 1.4 and are characteristic for both the equalizers 1 and 4
There is a disadvantage that the fluctuation of the frequency characteristic occurs if there is a
variation of. In addition, in order to drive an ordinary speaker with an amplifier for MFB
(amplifier), it is necessary to switch both the equalizers 1 and 4 together in order to change it to
an amplifier with flat frequency characteristics. In particular, the feedback amount of MFH can
be changed continuously. In this case, it is necessary to change both of the equalizer
characteristics in the same manner, which makes the circuit extremely complicated. For example,
FIG. 2 shows the frequency characteristics of each part in the conventional MFB, but the
equalizers 1 ° 4 have characteristics d and e, respectively, in order to use the sound pressure
characteristics af of the speaker before feedback. In this case, the equalizers 1 and 4 need to be
individually designed because they do not vary and two characteristics are related. That is,
assuming that the feedback amount '(i-1 + A.beta.), The gain decreases to 1 / (1 + A.beta.) After
feedback, so the gain of the equalizer 1 becomes 1 + A.beta. And the gain of the equalizer 4
becomes .beta. However, it is the gain before feedback from the input of the A power amplifier 2
to the output of the feedback amplifier 5. When the reproduction sound of the speaker 3 is
subjected to vibration detection and is fed back to the characteristic d 'of the equalizer 4 (ithrough to the power amplifier 2, when the equalizer 1 is the characteristic d, the sound pressure
characteristic of the speaker 3 changes the characteristic a by the feedback amount It becomes
characteristic C. In order to prevent positive feedback at the upper limit frequency of feedback,
the equalizer characteristic d is 6 dB / octave, and the characteristic C after feedback is as
described above] / (1 + Aβ). In order to make the characteristics as described above, it slightly
deviates from 6 dB / octave as shown in the equalizer characteristic e. Since one equalizer time
constant circuit that corrects this is not enough, multiple time constants are sufficient, and if the
variation of each constant is included, the characteristics of the time constant circuit are stable
compared to one equalizer 4 <<, Therefore, it is difficult to make the sound pressure
characteristic of the speaker after feedback always flat by continuously changing the
characteristic according to the feedback amount. OBJECTS OF THE INVENTION It is an object of
the present invention to provide an entire audio apparatus that can be engaged with MFB Th
with a simple configuration.
In the audio apparatus for detecting the operation or sound output of the vibration system of the
speaker and returning it to the input of the power amplifier for driving the speaker, the switch
for opening and closing the feedback loop can be used together with it A circuit is provided to
reduce the frequency characteristic of the amplifier. This eliminates the need for two
conventional equalizers as described later, which simplifies the circuit configuration and allows
embodiment of the present invention is shown in all of FIGS. That is, first, as shown in FIG. 3, the
equalizer 6 is inserted between the signal system side in the feedback loop, that is, between the
power amplifier 2 and the subtractor 7. The other reference numerals are the same as in FIG. As
shown in FIG. 4, when the frequency characteristic of the equalizer 6 is the characteristic g, the
sound pressure characteristic of the speaker 3 before feedback is corrected from the
characteristic a to the characteristic f, and the high region becomes 6 dB / octave. When
feedback is applied in this state, the lowest low frequency reproduction limit frequency is
lowered as shown by the characteristic b ', and the same characteristic as the characteristic of the
conventional FIG. 2 can be obtained. With this configuration, one equalizer is sufficient, and
when not used as an MFB, it is sufficient to flatten the equalizer 6 and fully open the input of the
feedback circuit 5. FIG. 5 shows a specific circuit example, which is constituted by an operational
amplifier 9 having an equalizer 6 total time constant R1C unit 2 time constant R2C1, corrected
so that all characteristics g from the input 8 to the output 10 become, and a feedback signal from
the input 11 Are fed back to the inverting input of the operational amplifier 9 by the operational
amplifier 12 via the switch S. Although FIG. 5 shows a state in which the MFBE is applied, if the
contact A is also turned to the contact B when the interlocked switch S is +82, the capacitor C □
is shorted and the feedback human power 1 is disconnected, and the input The characteristics
from 8 to 10 are flat and become a normal amplifier. FIG. 6 is a modified example, and the switch
S in FIG. (5) By replacing S2 with variable resistor VR and VH2 respectively, the feedback amount
is changed continuously and at the same time the equalizer characteristics gf are continuously
changed and the reproduction characteristics of the speaker are flat! F from the low range
regeneration limit (fo) without MFB continuously. The whole change is made to be able to be
made, and when the variable resistor vR1 is infinite and the variable resistor ■ is narrowed, it
can be used as a normal amplifier. Conventionally, since there is no switch or volume as
described above, the amplifier for MFB is dedicated to the MFB and can not be driven in all
normal speakers.
Therefore, the new power amplifier itself has become a burden to users, and it has been a
negative cause for the spread of D and MFB systems. In this respect, according to the present
invention, such a point can be solved with a simple configuration, can be configured at low cost,
and its utility value is great. In the embodiment, the equalizer is configured by the operational
amplifier 9. However, when the power amplifier itself has the characteristics of the equalizer
characteristic g, the operational amplifier 9 becomes unnecessary (6), which also has the
advantage of being able to be configured inexpensively. Also, in the ones in Fig. 2 and Fig. 4, Q
stands by phase rotation in the low band (simplification / abbreviated explanation is omitted), but
this point is as indicated by so-called speaker acceleration feedback theory. There is no particular
difference in the present invention. Effect of the Invention The audio device of the present
invention has an effect that the MFB can be disengaged with a simple configuration and the cost
can be reduced.
Brief description of the drawings
1 is a block diagram of a conventional MFB, FIG. 2 is a sound pressure frequency characteristic
diagram of each part thereof, FIG. 3 is a block diagram of MFH showing the principle of one
embodiment of the present invention, and FIG. Sound pressure frequency characteristics, FIG. 5 is
a specific circuit diagram of the MFB, and FIG. 6 is a circuit diagram of a modification thereof.
2 · · Power amplifier, 3 · Speaker, 5 · · · Feedback amplifier (feedback circuit), 6 · · · Equalizer, 7 · · ·
Subtractor, 9. 12 · · · op amp, S engineering, S2 switch, VR engineering . ■ ・ ・ ・ Variable
resistor (switch), R work, R2, C work · time constant (flat circuit) substitutes Patent attorney
Patent attorney 暎 失 図 1 figure □ 囚 ((Hz) Figure 2 · · Fig. 3 @ @ Liangaki (Hz) Fig. 4
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