JPH07162990

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DESCRIPTION JPH07162990
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
sound reproducing apparatus for detecting reproduced sound of a speaker used in various kinds
of audio equipment with a microphone and correcting the reproduced sound of the speaker
according to this detection signal.
[0002]
2. Description of the Related Art A conventional sound reproducing apparatus of this type will be
described with reference to the drawings.
[0003]
FIG. 6 is a block diagram showing the configuration of a conventional sound reproducing
apparatus, in which a signal input to an input terminal 12 is amplified by a power amplifier 14
through a subtractor 13 and an output signal of the power amplifier 14 is reproduced by a
speaker 15. A microphone 16 detects an acoustic output signal emitted from the speaker 15 and
amplifies it by the microphone amplifier 17 and then connects it to the negative input terminal of
the subtractor 13 connected to the input terminal 12 through the filter 18 to provide a negative
feedback loop. To form the
[0004]
However, in the above-described conventional configuration, the phase difference between the
electric signal input to the speaker 15 and the acoustic output signal emitted from the speaker
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15 is disturbed as shown in FIG. A negative feedback occurs near 0 °, but a positive feedback
occurs around + 180 ° or -180 °, which causes a problem that a very unstable feedback system
can not provide sufficient negative feedback.
[0005]
In addition, when the band is limited by the filter 18 in order to secure the oscillation margin,
there is a problem that it is limited to only a certain limited frequency band and the sound output
can not be sufficiently improved. The output sound pressure frequency characteristics of the
conventional sound reproduction apparatus are shown in FIG.
[0006]
An object of the present invention is to solve such conventional problems and to provide a sound
reproduction device capable of exhibiting stable characteristics.
[0007]
SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, a sound
reproducing apparatus according to the present invention comprises an acoustic tube for guiding
a sound wave to the front of a speaker for reproducing an output signal of a power amplifier and
The microphone for detecting the sound output signal is arranged close to the front surface of
the diaphragm of the speaker.
[0008]
With this configuration, the stability of the feedback circuit can be improved and the amount of
feedback can be increased, and the acoustic characteristics of the acoustic tube and the speaker
coupled with the acoustic tube can be improved.
[0009]
DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) A first embodiment of
the present invention will be described with reference to the drawings.
[0010]
FIGS. 1 (a) and 1 (b) are a plan sectional view and a side sectional view showing the configuration
of a speaker to which an acoustic tube for guiding a sound wave used in the acoustic reproducing
apparatus according to the embodiment is coupled. An acoustic tube 2 for guiding a sound wave
is connected to the front of the speaker 1, and a sound is emitted from an opening having a
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narrow rectangular slit. In order to suppress the resonance of the acoustic tube 2, the acoustic
tube 2 is used. A speaker 1 in which sound absorbing members 3 are disposed on both sides to
form a throat 4 to be a sound path of the speaker 1 and a microphone 6 is installed about 5 cm
from the opening of the speaker 1 The sound output signal emitted from the microphone is
detected by this microphone 6, and feedback is applied using this detected sound output signal.
[0011]
FIG. 2 is a block diagram showing the configuration of the sound reproducing apparatus of this
embodiment, and the input signal amplified from the input terminal 7 through the subtracter 8
by the power amplifier 9 is shown in FIGS. 1 (a) and 1 (b). The sound tube 2 shown is reproduced
by the coupled speaker 1, the sound output signal emitted from the speaker 1 is detected by the
microphone 6, the output of the microphone 6 is amplified by the microphone amplifier 10, and
the output signal and the input terminal The output signal of the subtracter 8 connected to 7 is
subjected to addition / subtraction processing (addition or subtraction) by the adder / subtractor
11 and then connected to the negative input terminal of the subtractor 8.
[0012]
The transfer characteristic of this circuit is T (S), the transfer characteristic of the power
amplifier 9 is A, the amplification degree of the adder / subtractor 11 and the subtracter 8 is 1,
Vin Is expressed as an input voltage and Vout as an output voltage of the power amplifier 9, Vout
/ Vin = A / (2 + A · T (S))
[0013]
Similarly, the transfer function of the block diagram of the sound reproducing apparatus
described with reference to FIG. 6 in the prior art is: Vout / Vin = A / (1 + A · T (S))
[0014]
That is, when T (S) is almost considered to be the transfer characteristic of the speaker 1 because
the characteristic of the microphone 6 is almost flat, the phase change due to the resonance of
the speaker 1 and the acoustic tube 2 makes T (S) negative. When it becomes 1 (the phase is
reversed) and the amplification degree of the power amplifier 9 is A = 1, in the conventional
circuit, the denominator becomes 0 and it becomes a condition to oscillate.
However, it is understood that the transfer characteristic of the present invention is 1 and it is
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possible to secure the stability of the feedback under the same conditions.
[0015]
FIG. 3 compares frequency characteristics before and after feedback is actually applied, and FIG.
4 shows frequency characteristics of the power amplifier 9 when feedback is applied.
[0016]
(Embodiment 2) The following Embodiments 2 to 4 describe an embodiment where the
arrangement position of the microphone is changed, and a second embodiment of the present
invention will be described with reference to the drawings.
[0017]
FIG. 5 is a cross-sectional view showing a speaker to which an acoustic tube of the sound
reproducing apparatus according to the embodiment is coupled, and is located at a position 6a at
a distance of about 1 cm so as to be close to the front surface of the diaphragm (not shown) A
microphone is arranged.
[0018]
Thus, by the microphone disposed close to the front surface of the diaphragm of the speaker 1,
the frequency characteristic of the speaker 1 and the characteristic of the acoustic tube 2 can be
simultaneously detected, and the frequency characteristic can be controlled.
[0019]
(Third Embodiment) The third embodiment of the present invention will be described below with
reference to the drawings.
[0020]
FIG. 5 is a cross-sectional view showing a speaker in which the sound tube of the sound
reproducing apparatus according to the embodiment is combined. In this embodiment, the sound
pressure of the primary resonance of the sound tube 2 is maximized at the position 6b where the
microphone is arranged. The acoustic tube 2 is disposed at the inside of the acoustic tube 2 at a
distance of 1/3 of the length of the acoustic tube 2 from the start end to the end of the acoustic
tube 2 which is a position.
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[0021]
By disposing the microphone at this position 6b, in particular the characteristics of the acoustic
tube 2 can be corrected.
[0022]
Fourth Embodiment The fourth embodiment of the present invention will be described below
with reference to the drawings.
[0023]
FIG. 5 is a cross-sectional view showing a speaker to which the sound tube of the sound
reproducing apparatus according to the embodiment is coupled. In this embodiment, a position
6c for arranging a microphone is arranged inside the end vicinity of the sound tube 2. It is a
thing.
[0024]
By arranging the microphone at this position 6c, the distance from the speaker 1 to the
microphone is long, so it is possible to control mainly the characteristics from the bass range by
the speaker 1 and the acoustic tube 2 to the primary resonance of the acoustic tube 2 It is.
[0025]
As described above, according to the sound reproducing apparatus of the present invention, it is
possible to correct the disturbance of the characteristics of the speaker and the sound tube
coupled to the front surface, and obtain the flat sound characteristics. It is possible to easily
realize the characteristics that can not be realized by the equalizer used for the characteristic
correction, and furthermore, even if the frequency characteristics of the speaker and the acoustic
tube change to some extent because the detection signal of the microphone is a reference It has a
special effect that the frequency characteristics can be corrected in a straightforward manner,
and its contribution is great.
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