JPS6174497

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DESCRIPTION JPS6174497
[0001]
FIELD OF THE INVENTION The present invention relates to a speaker device for high fidelity
reproduction. Configuration of the Conventional Example and its Problems Conventionally, there
is a monyon feed panoc (MFB) as a method of lowering the low range reproduction limit of the
speaker system, and among them, the reproduction sound of the speaker is detected by the
microphone and There is an acoustic feedback system in which an output is fed back to a
speaker via an amplifier. Such a conventional acoustic feedback speaker device will be described
below. FIG. 1 is a block diagram of a conventional MFB system, in which a microphone 4 is
provided on the pan-full plate 2 to detect the radiation sound of the speaker 3, and the output is
fed back to the amplifier 80 inverting input end to apply negative feedback to the speaker 3. ing.
Note that a single speaker box, 5 is a holder, 6 is a speaker drive code, 7 is a microphone output
signal code, and 9 is an input child. In general, the microphone is provided with a vent hole in a
part of the microphone case so that the diaphragm does not shift in one direction due to the
pressure difference between the surface and the back of the film when the atmospheric pressure
changes, to balance with the atmospheric pressure. I have to. Even in the case of a nondirectional
microphone, it is necessary to open a vent. Therefore, when the microphone 4 is attached to the
speaker box 1 as shown in FIG. 1, if the output signal output portion 11 of the microphone 4 is
not complete, the pressure in the speaker box 1 (hereinafter referred to as back pressure)
However, where only the sound pressure from the surface of the microphone 40 should be
detected, the sound pressure on the back of the microphone 4 is also detected. In this case, since
the sound pressure on the surface of the microphone 4 and the back pressure are opposite in
phase, it is not possible to apply negative feedback due to the sound pressure on the surface of
the microphone 4 and it becomes positive feedback, and oscillation occurs when a predetermined
condition is exceeded. There was a problem of reaching the SUMMARY OF THE INVENTION The
present invention solves such a problem and correctly detects and controls the sound pressure
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radiated from the speaker box to the back of the microphone without the back sound pressure
inside the speaker cabinet being applied. The purpose is The present invention relates to a
speaker apparatus for applying MFB using a microphone, wherein a back chamber is provided at
the back of the microphone and this back chamber is in communication with the outside air. In
this way, unnecessary back pressure is not applied to the microphone, and as a result, accurate
MFB based only on the sound pressure from the speaker can be applied. Description of the
embodiment Fig. 2 shows an embodiment of the present invention, and the difference from Fig. 1
is that a back chamber 12 and a hole 10 are provided at the rear of the microphone.
Reference numeral 5 denotes a holder for holding the microphone 4. In general, it is desirable to
use a cushioning material such as rubber in order to reduce mechanical transmission of the
shock applied to the speaker box 1 to the microphone 4. As described above, in the embodiment
of FIG. 2, by providing the back chamber 12 behind the microphone 4, the sound pressure in the
speaker box 1 is not directly applied to the back of the microphone 4. Furthermore, a hole 10 is
provided in the holder 5 of the microphone 4 so that the internal pressure of the back chamber
12 and the external pressure become equal. In this configuration, the output signal output
portion 11 of the microphone 4 is not completely sealed, and the pressure inside the speaker box
1 flows into the back chamber 12 of the microphone 4 through the gap of the output signal
output portion of the microphone 4. Also, since the air escapes through the hole 10, the pressure
applied to the back of the microphone 4 can be greatly reduced as compared with the prior art. 3
and 4 are diagrams showing the effect. The broken line a in FIG. 3 shows the output signal
characteristics of the microphone 4 when the hole 10 is closed by sealing, and the solid line
shows the output signal characteristics measured in the state where the hole 10 is opened. The
vertical axis represents the output voltage of the microphone 4. Further, a solid line C in FIG. 4 is
obtained by measuring the sound pressure inside the speaker box 1 by inserting the microphone
4 into the speaker box 1 with the hole 1Q sealed. This data indicates that when the hole 10 is
sealed, the sound pressure inside the speaker box 1 (actual C in FIG. 4) flows from the output
signal output portion 11 of the microphone 4 into the back chamber 12 and is proportional to
the influence on the back of the microphone 4 Compared to the output signal of the microphone
4 when the hole 10 is open (FIG. 3 actual b), the output signal when the hole 10 is sealed (broken
line & FIG. 3) is , Indicates that it is rising in the bass. It was also confirmed that when the hole
10 is sealed in a state where the negative feedback is applied to the speaker 3 actually,
oscillation occurs in the low frequency. This is because the sound pressure inside the speaker
box 1 is inverted in phase with the sound pressure of the outside of the speaker box 1 because
the phase is reversed, and the output signal of the microphone 4 is further inverted in bass, and
becomes positive feedback. Especially when motional feedback is applied to the speaker to raise
the reproduction level in the low range, it is more advantageous to seal the speaker bonox 1, so
motional feedback is not applied to the bass in the closed speaker box 1. A signal of a level
higher than the state is applied to the speaker 3, and the pressure inside the speaker box 1
becomes extremely high.
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Also, if you want to go up to the bass level in the honhonaru feed Hanok, the speaker box 1 is
small. Before the feedback is applied, the pressure inside the speaker box 1 is higher because the
minimum resonance frequency determined by the diameter of the speaker diaphragm and the
volume in the box is high. In addition, it is extremely difficult to completely seal even if the
output signal output portion 11 of the micro-pong 4 is fully sealed, or to inspect each product
one by one while mass-producing it requires many man-hours, It is practically impossible to
ensure that it is completely sealed. In that respect, according to the present embodiment, the
above problems can be solved at once by providing the back chamber 12 and the opening 10,
and the sealing performance in the taking out portion 11 can be simplified. . FIG. 5 shows a
second embodiment of the present invention. This is a variable volume 16 for projecting the
cylindrical boss 13 integrally from the baffle plate 2 of the speaker box 1 and making the output
level of the microphone 4 output variable or the output level of the microphone 4 variable at the
tip thereof. The printed circuit board 14 on which the components are mounted is screwed to
configure the back chamber 12, and the back chamber 12 is shared as a room for storing the
head amplifier 16 and the like. Also in this case, the tightness between the printed circuit board
14 and the boss 13 can not be sufficiently maintained only by the packing or the bond, but since
the hole 1o is provided in the back chamber 12, the inside of the back chamber 12 and the
outside air are the same. Since the pressure can be greatly reduced and the compressed pressure
in the speaker box 1 is applied to the back of the microphone 4 as in the conventional case, the
control system oscillates because the sealing is uncertain. It does not occur. As described above,
according to the present invention, it is not necessary to perform sufficient sealing processing in
the output signal extraction portion of the microphone, and the control of the sound pressure
detection type speaker using the microphone reliably and stably. It is possible to improve the
reliability by knowing the oscillation in the bass. Also, since there is no detection of a signal with
a large amount of distortion inside the speaker from the back of the microphone, it can be
detected with little distortion as a sensor, and as a result, a high-performance speaker can be
configured and reverse from the back The margin leading to oscillation is increased by the
number at which the phase signal is reduced, and the amount of control (the amount of feedback
of the sound pressure of the speaker) is increased by that amount, whereby a speaker with
higher performance can be configured.
[0002]
Brief description of the drawings
[0003]
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1 is a block diagram of a conventional speaker apparatus, FIG. 2 is a block diagram of an
embodiment of the present invention, FIG. 3 is an output sound pressure characteristic of a
detection microphone, and FIG. 4 is a sound pressure inside a speaker box FIG. 5 is a crosssectional view of the microphone mounting portion in the second embodiment of the present
invention.
1 · · · Speaker box, 2 mountain bar '7 full board, 3 · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · ·.・ ・ ・
Speaker driving code, 7 ・ ・ ・ ・ ・ Microphone output signal code, 8 ・ ・ ・ ・ ・ Amplifier
19 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ 11 · Cord
withdrawal portion, 12 · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · IJ 7 board, 15 · · · · · · · · · · · · ·
· · · · Semi-fixed volume. Name of the agent Patent attorney Nakao Soft man and one other person
Figure 1 Figure 2
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