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JPS57122990

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DESCRIPTION JPS57122990
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a frequency characteristic diagram when a
high cut filter is used in the conventional MFB system, FIG. 2 is a block diagram of an improved
MFB speaker circuit, and FIG. 3 is a circuit of FIG. Fig. 4 shows the frequency characteristics of
the speaker input voltage when MFB is applied, Fig. 5 is a block diagram showing the MFB
speaker circuit according to the present invention, and Fig. 6 shows one embodiment of the
feedback variable circuit. FIG. 7 is a block diagram showing another embodiment of the feedback
amount variable circuit. 1 ...... speaker, 3 ...... detector, 4 ...... level adjusting circuit, 5 ......
comparator circuit, 6 ...... high cut filter, 7 иииииии Feedback amount variable circuit, 8 ииииии Op amp, 9
иииииии Level sensor, 10 иииииии Variable gain amplifier.
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a motional
feedback (hereinafter referred to as M0255FB) speaker circuit. Conventionally, in order to
improve the acoustic characteristics of a speaker, a speaker circuit having an MFB that detects
the motion of the vibration system of the speaker, feeds back the detected output to the drive
amplifier system of the speaker, and controls the vibration of the speaker. It has been used. Thus,
when the vibration detection signal of the speaker is fed back to the amplifier system, the sound
pressure characteristic of the speaker is proportional to the acceleration of the vibration system,
and the feedback \ signal amount 1 middle high M ? ? ? ? ?multiple low low t-t + Nof 1!
'The sound pressure level in the high region is lowered, and the speaker's low frequency
resonance frequency fo is relatively lowered, and the bass reproduction range can be expanded.
In general, since the multi-way system is used for the Scheikanostem, in the case of the
expansion of the low-weight regeneration area, the woofer is subjected to MFB to lower fo.
However, when the acceleration detection signal is directly fed back to the amplifier, the sound
pressure level of the woofer is lowered by the feedback, so that the balance of the sound with the
high sound speaker such as the tweeter / skoker changes. Furthermore, when the feedback
amount increases, the sound pressure level difference between the woofer and the treble speaker
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also increases, so it is necessary to adjust the level of the coha and the treble speaker according
to the 0264 feedback IK. In addition, as the frequency of the diaphragm of the speaker increases,
the level and the phase of the acceleration resonance of the vibration system in the high region
including the division resonance are disturbed as the frequency increases. If the detection signal
at this time is fed back to the amplifier, it is inconvenient to disturb the speaker characteristics.
There is a method of inserting a high-cut filter to remove this high-range disturbed signal, but
with this method it is possible to remove the high-range disturbed signal, but the sound pressure
characteristics of the speaker are shown in FIG. It becomes flat in the middle and high range as
shown. In addition, in FIG. 1, the solid line gives feedback; 6 ?, ?, ?7 ? 7, therefore ? ? ?.
????? Therefore, in order to flatten the sound pressure characteristics in the middle and
high frequencies, it is necessary to change and correct the frequency characteristic of the gain of
the amplifier. However, return 11! It is necessary to adjust the frequency characteristic for
correction according to the problem; the adjustment is complicated. Therefore, an improved MFB
speaker circuit as shown in FIG. 2 has been proposed. The method shown in FIG. 2 inputs the
detection signal of the speaker ? ? ? ? and the original power signal to the amplifier into the
comparison circuit, and the output of the comparison circuit 102 ░ 55 is fed back to the
amplifier through the high cut filter. The level of the detection signal is preset to be the same as
the level of the input signal.
For this reason, the output from the comparison circuit is approximately zero in the middle
range, and the high-range disturbed signal passes through the high cut filter, so the feedback
amount to the amplifier becomes approximately zero, and the input voltage to the speaker is all It
has no effect. On the other hand, in the low frequency range, the shortfall is obtained as the
output of the comparison circuit, and the output is fed back to increase the input voltage of the
speaker, so that the shortfall is automatically compensated and flat characteristics are obtained.
The frequency characteristics of the sound pressure level in this method are shown in FIG. 6 at
211, and the solid line shows the case where the feedback amount is increased in order before
the feedback, while the dashed line and the one-point chain line. . According to this method, the
sound pressure level in the middle to high range does not decrease even if feedback is
performed, the bass range can be expanded, and the setting of fo can be facilitated by the
increase of the feedback. The frequency characteristic of the input voltage to the speaker in this
method is shown in FIG. In FIG. 4, the fact that it is 0 (dB) is the same as the original input to Spy
0286 when MFB is not applied, and it is said that the input voltage is not affected by MFH at all.
is there. Also, as is apparent from FIG. 4, it is approximately 10 dB at approximately zero and at
most fo (low band) at fo and above (middle high band) of the five-element speaker, and it is
approximately 10 dB at low band compared to when no MFB is applied. Several times the voltage
is input as an input. However, in this method, when the original input to the speaker becomes
large, the input voltage to the speaker in the low range is several times higher than when the
MFB is not applied, so there is a margin in the output voltage of the amplifier. At the same time,
the input voltage to the speaker is clipped. Because the bass region is broadened by MFB and
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distortion due to clipping is increased, the power supply voltage of the amplifier should be
several times higher than in the conventional case to sufficiently obtain the effect of MFB. For
example, in the case of an amplifier used for a tape recorder or a radio, not only there is no
margin for the output voltage, but it is not practical because it is necessary to increase the
number of used electric oils for the increase of the power supply voltage of the amplifier. Even
mid-class amplifiers for TVs and the like have problems with the thermal characteristics of the
amplifiers themselves and the IC circuits used when raising the output voltage, which is
expensive and not practical. Also, there is a limit to the allowable amplitude of the speaker itself,
and when a large input is applied to the speaker, if the low frequency input is further increased
by the MFB, the speaker characteristics are deteriorated beyond the allowable amplitude of the
speaker. It will be Jin. Therefore, an object of the present invention is to provide an MFB speaker
circuit which solves the above-mentioned points.
The details will be described below with reference to the drawings. FIG. 5 shows an MFB speaker
circuit according to the present invention. In FIG. 5, (1) is a speaker, (2) is an amplifier for driving
the speaker (1), (3) is a detector for detecting the vibration of the speaker (1), (4) is a detector (3)
Detection level 16 from the level adjustment circuit to perform level adjustment;? The output of
the level 1 # adjustment circuit (4) and the signal to the speaker (1) aqat-1v-i, a2 * oo *, f6Jl [! A
high cut filter through which the output of (1 m 1 il) +51 passes, (7) is a feedback variable circuit
that receives the output from the high cut filter 16 and varies the feedback to the amplifier (2).
FIG. 6 is a diagram showing a feedback amount variable circuit -1 (I (Q8 embodiment), and FIG. 7
is a diagram showing another embodiment. In FIGS. 6 and 7, (8) is an operational amplifier, (91H
level sensor, low is a variable gain amplifier whose gain changes in proportion to the output of
the level sensor (91). First, in FIG. In the circuit shown, the input of the level sensor (9) uses the
output of the operational amplifier (8). The input to the level sensor (9) is rectified by a rectifier
built in the level sensor (9) or an external rectifier, and the input signal of the level sensor (9) is
selected by appropriately selecting the time constant of the rectifier. The envelope signal of the
signal is the output of the level sensor 9. Also, the gain of the operational amplifier (8) is ? и, the
amount of feedback from the output terminal to the input negative terminal! r is inversely
proportional. Here, when the input ? v1 and the output to the operational amplifier (8) are Vo,
and the gain of the variable gain amplifier (ffl is G, Vo??Vi / G is obtained. Here, since the gain
G of the variable gain amplifier Q1 is proportional to the input of the level sensor (9) (ie, the
output of the operational amplifier (8)), it becomes GoclVol. ?????????? From the
equation (1) and the equation (2), it becomes Vo flash Vi and becomes VolIVoloclJVTl. As
apparent from +31 (3), the circuit shown in FIG. 6 works as a 1-W power compression circuit.
The feedback signal passes through the compression circuit and is then fed back to the amplifier
(2). Therefore, when the input to the speaker (1) is large, the amount of feedback is suppressed,
and when the input is small, the amount of feedback is large. Next, to explain the case where the
circuit shown in FIG. 7 is used, the input force in which 1 M of feedback signal is flowed by the
rectifier circuit ?? is input to the negative input terminal of the operational amplifier (8) and
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the DC voltage of + vB is input to the positive input terminal. The output voltage of the
operational amplifier (8) is vslVi'l.
Here, Vi 'is the level of the feedback signal human power Vi: \ Bi- \, which is the rectified voltage
after adjustment-When the feedback signal amount is small, the output of the output (op-amp
18) of the level sensor (9) Is approximately + vB, and the gain is large, but the output of the
operational amplifier (8) decreases as the amount of feedback signal increases, and the gain of
the 0T table и и и the amplifier decreases. When a large input is applied, the output of the op amp
(8) becomes negative and the current flows in reverse, and there is a risk of destroying the
variable gain amplifier uI, so insert a diode between the op amp (8) and the level sensor (9) To
prevent backflow. The output of the level sensor (9) at this time is substantially zero, and the gain
of the variable gain amplifier 01 is also substantially zero. That is, even when the input to the
speaker is large, it is possible to reduce the feedback signal amount and to suppress the increase
of the input electrons to the speaker. As described above in detail, according to the present
invention, when the input voltage to the speaker is large, the increase in the input voltage to the
speaker by the MFB is suppressed, and when the input voltage is small, the feedback is
sufficiently performed. Since the effect is sufficiently exerted, it is possible not only to suppress
an increase in distortion caused by clipping of the output voltage of the amplifier and the
allowable amplitude of the sbi ? force which has conventionally occurred at large input, but also
to the power supply of the amplifier. There is no need to increase the voltage to a large extent.
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