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JPH09284882

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DESCRIPTION JPH09284882
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
sound reproducing apparatus, and more particularly to a sound reproducing apparatus in which
good high sound quality reproduction and low sound quality reproduction are performed.
[0002]
2. Description of the Related Art Conventionally, in a speaker system, a speaker unit is attached
to a cabinet. In this structure, when the cabinet is small, the compliance of the air on the back
surface is reduced, and the vibration of the diaphragm is limited. As a result, the lowest
resonance frequency fo of the speaker is increased and the bass is not output. Furthermore, since
the front and back compliance is different, distortion does not occur uniformly in the front and
back, resulting in distortion.
[0003]
Therefore, an extremely large cabinet is required to remedy this. As another structure, there is a
rear surface release type shown in FIG. 5. In this structure, the compliance of air before and after
the speaker is the same, and although distortion due to this is not generated, the sound emitted
behind travels forward. There are problems such as interference with the sound radiated before
and disturbance of the characteristics or reduction of the bass. In order to prevent such a
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1
phenomenon, a baffle of several meters square is required, and there was a problem in practical
use.
[0004]
In the speaker system invented and filed by the present applicant for solving this problem
(Japanese patent application 5-9094), as shown in FIG. 6, the speaker for reproduction on the
upper end face 32 side of the duct-like cabinet 31 A unit 33 is disposed, a detection microphone
34 for detecting a sound radiated from the rear of the unit is disposed in the vicinity of a speaker
unit for reproduction, and a sound radiated from the lower end surface 35 of the cabinet 31 is
further disposed. The muffling speaker unit 36 and the monitoring microphone 37 are disposed
in the vicinity of the end face 35 for controlling the noise. In this system, the delay time for
generating the muffling signal with the signal from the detection microphone 34 as a reference
signal is obtained for the length of the duct. Therefore, the duct needs to have a certain length (at
least about 50 cm), making it difficult to miniaturize.
[0005]
As described above, in the conventional sound reproducing apparatus, a large baffle is required
to prevent the disturbance of the characteristics due to the interference of the sound radiated
from the back of the speaker for reproduction, and the length of the duct is long. It was difficult
to miniaturize the system.
[0006]
The present invention has been made to solve this problem, and an object thereof is to provide
an audio reproduction apparatus that can achieve good sound quality reproduction and bass
reproduction even with a small speaker system.
[0007]
SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, in the present
invention, a signal to be input to a muffling speaker is reproduced in approximately the time
necessary for processing a reproduction signal as a reference signal. By delaying the
reproduction signal input to the speaker, it is possible to cancel the sound on the back surface
simply by guiding the sound to the place of the muffling speaker by providing a short lead-out
path without needing the length of the duct physically I made it.
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2
[0008]
In general, in a speaker system with an open back, the sound radiated to the back of the speaker
turns to the front and interferes with each other, and the sound wave phase is low in a long
wavelength low band where the length of the looping can be ignored. Conversely, when the
length of the looping path is equal to the wavelength, the sound of the frequency is no longer
output.
Conversely, at frequencies where the looping path length is half the wavelength, the sounds
become stronger as they strengthen each other.
[0009]
As described above, in order to disturb the characteristic and make the low band disappear from
the rear side, a cabinet is usually provided so that the sound from the rear side is not allowed to
flow to the front side as it is.
However, if the cabinet is small, the compliance of the air on the back side is reduced, and the
vibration of the diaphragm is limited. As a result, the lowest resonance frequency fo of the
speaker is increased and the bass is not output.
Furthermore, since the front and back compliance is different, distortion does not occur
uniformly in the front and back, resulting in distortion.
[0010]
In order to eliminate the above phenomenon, the present invention does not open the back
surface and raise the fo (minimum resonance frequency) and does not generate an amplitude
distortion due to air compliance, so the sound coming from the back surface is the front surface.
It was made to cancel out with the muffling speaker so that it did not go around.
[0011]
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In order to realize this, in the conventional example, a duct is provided on the back of the speaker
unit for reproduction, and a detection microphone for detecting sound emitted from the rear of
the unit is disposed on one end face of the duct, Furthermore, although the speaker unit for
muffling to cancel the sound of the back emitted from the other end face of the duct and the
monitoring microphone for monitoring the muffling state were arranged near the end face, this
system detects The delay time corresponding to the time for generating the mute signal from the
reference signal detected by the microphone for the length of the duct is obtained.
Therefore, the speaker system needs a certain length (at least about 50 cm), and miniaturization
has been difficult.
[0012]
Therefore, in the present invention, the reference signal does not depend on the detection
microphone, but the reproduction signal input to the reproduction speaker is used, and the signal
to be input to the muffling speaker is derived from the reproduction signal as a signal input to
the reproduction speaker. By using the reproduction signal delayed by the time necessary for
processing, there is no need for the duct length physically, and a short lead-out path is provided
for the sound on the back side to make the sound to the place of the muffling speaker It became
possible to cancel only by leading.
[0013]
Embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a front view and a sectional view showing a speaker system of a sound reproducing
apparatus according to a first embodiment of the present invention, and FIG. 2 is a circuit
diagram of the sound reproducing apparatus. 1 (a) and 1 (b), 1 is a reproduction speaker, 2 is a
muffling speaker, 3 is a short cylindrical guide wall for guiding the sound on the back of the
reproduction speaker so as to be easily muffled, 4 is a A cabinet formed of a closed box for a
muffling speaker, and 5 is an error detection microphone for confirming whether or not the
muffling is performed.
[0014]
The speaker system may have a structure in which the magnetic circuits are fixed by arranging
the reproduction speaker 1 and the muffling speaker 2 back to back as shown in FIG. 1C.
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[0015]
In FIG. 2, the analog signal output from the playback device 6 such as music is converted into a
digital signal by the Α / D converter 7 and is an approximation of the transfer characteristics of
the delay device 15, the adaptive filter 8 and the cancellation system, respectively. It is input to
the FIR digital filter 11 which convolutes a certain C hat.
If the signal from the reproduction device 6 is a digital signal, the A / D converter 7 is not
necessary.
[0016]
For the reproduction signal input to the delay device 15, the adaptive filter 8 generates a
muffling signal by the delay device 15 so that the signal output from the muffling speaker 2 can
properly cancel the sound on the back surface of the reproduction speaker 1 An appropriate time
(for example, 5 msec to 10 msec or so depending on the performance of the processing
apparatus) is delayed and output. Further, the output signal is converted to an analog signal
through the D / A converter 16, amplified by the power amplifier 17, and emitted from the
reproduction speaker 1.
[0017]
The adaptive filter 8 is controlled by a controller 12 in which an LMS algorithm, which is a
representative algorithm of the adaptive filter, is incorporated as an algorithm for controlling the
adaptive filter 8. As a reference signal used for the control device 12, a signal obtained by
convoluting a C hat obtained by approximating the transfer characteristic C of the cancellation
system by the FIR digital filter 11 with the signal from the A / D converter 7 is used.
[0018]
That is, the controller 12 uses the signal from the FIR digital filter 11 as a reference signal,
converts the output signal of the adaptive filter 8 into an analog signal through the D / A
converter 9, amplifies it by the power amplifier 10, and amplifies the mute speaker It controls so
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that the sound of the back emitted from 2 and emitted from the speaker 1 for reproduction |
regeneration is canceled.
[0019]
As an error signal, a signal from the error microphone 5 is amplified by the microphone amplifier
18, and a band elimination filter is performed to control only a band in which the sound coming
around from the rear has a wavelength that cancels the front sound. The A / D converter 13
converts the digital signal into a digital signal and inputs the digital signal to the control device
12.
In the embodiment, if the speaker aperture is about 16 cm and the guide wall is about 3 cm, the
band eliminate filter 14 has an elimination band of about 2.2 to 2.6 KHz at the center of 2.4 KHz.
[0020]
From the discrete signal X (n) output from the A / D converter 7 and the discrete signal e (n)
output from the A / D converter 13, the evaluation function of Je = {e (n)} 2 is minimized The
filter coefficients of the adaptive filter 8 are determined by the LMS algorithm, which is one of
the steepest descent methods, and updated and set in the adaptive filter 8.
[0021]
Assuming that the adaptive filter 8 is composed of an I-order FIR digital filter, the ith filter
coefficient of the adaptive filter 8 is wi (where i = 0 to I), and the adaptive filter 8 to the A / D
converter 13 Assuming that the j-th filter coefficient is cj (where j = 0 to J) when the C hat
obtained by approximating the cancellation transfer characteristic C of the transmission path up
to The filter coefficient w of the adaptive filter 8 at time tn is set to wi (n), and the filter
coefficient wi (n + 1) at time tn + 1 is updated and set for the adaptive filter 8 according to the
following equation.
wi (n + 1) = wi (n) + α · γ e (n) · q * (n−i) The term value wi (0) is set to a predetermined value.
03-05-2019
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[0022]
By adapting the adaptive filter 8 in this way, the sound radiated to the front among the radiated
sounds actually becomes reproduced sound and reaches the listener, and the sound radiated to
the back is canceled by the muffling speaker It will not come out as a sound. As a result, the
sound emitted from the front has the same characteristics as if the speaker were attached to an
infinite cabinet, and the sound emitted from the front has the same characteristics as the sound
from the sound coming from the back. Distortion due to the difference in compliance is
eliminated, and sufficient bass reproduction is possible. Since the muffling speaker 2 is attached
to the cabinet 4, it does not emit sound from the back.
[0023]
As described above, the control system in FIG. 2 always operates so that the muffling speaker
cancels the sound on the rear surface of the reproducing speaker in a predetermined band, and
the state of the periphery of the speaker due to aging of the speaker and installation conditions
Optimal cancellation can always be performed regardless of changes in
[0024]
By the way, the secular change of the speaker is not so large, and the change of the transfer
characteristic of the cancellation system in the installation situation is not so large.
From this, it is also possible to fix the filter coefficient wi of the adaptive filter 8 in FIG. 2 in order
to simplify the control system and reduce the cost.
[0025]
The second embodiment has such a configuration, and the speaker system is configured as
shown in FIG. 1 except for the error microphone 5, and the circuit is configured as shown in FIG.
[0026]
In FIG. 3, as in FIG. 2, the signal output from the reproduction device 6 such as music is
converted into a digital signal by the A / D converter 7 if the signal is an analog signal, and the
delay device 15 and FIR are respectively transmitted. It is input to the digital filter 19.
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7
[0027]
The FIR digital filter 19 is a filter in which the adaptive filter 8 in FIG. 2 is fixed at an optimum
value, and includes the time delay required by the control device.
Then, the signal from the A / D converter 7 processed by the FIR digital filter 19 is converted to
an analog signal through the D / A converter 9 and then amplified by the power amplifier 10 and
emitted from the muffling speaker 2 It is configured to cancel the back sound emitted from the
reproduction speaker.
[0028]
Therefore, as in the case of FIG. 2, the delay unit 15 delays the signal from the A / D converter 7
by the delay of the FIR digital filter 19 and inputs it to the D / A converter 16, which is an analog
signal. The converted signal is amplified by the power amplifier 17 and emitted from the
reproduction speaker 1.
[0029]
In this way, in the second embodiment as well as the first embodiment, the sound radiated to the
front among the radiated sounds actually becomes the reproduced sound and reaches the
listener, The sound radiated to is canceled by the muffling speaker and does not come out as a
sound.
As a result, the sound emitted from the front has the same characteristics as if the speaker were
attached to an infinite cabinet, and the air compliance at the front and back of the speaker is
eliminated because sound interference from the sound from the back is eliminated. Distortion
due to the difference between
[0030]
In FIG. 2, the gains of the power amplifiers 10 and 17 are linked, and for example, when the gain
of the power amplifier 10 is doubled, the gain of the power amplifier 17 is controlled to be
doubled to increase the volume. Even in the state, the coefficients of the adaptive filter or the FIR
digital filter do not change.
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[0031]
By doing this, if the gain of the power amplifier 17 is increased to increase the volume of the
reproduced sound, the control system automatically increases the gain of the adaptive filter to
mute if the gain of the power amplifier for muffling is not increased. Therefore, it is possible to
prevent the level of the mute signal from exceeding the range of the D / A converter 9 and
preventing the operation from being wrong.
[0032]
Similarly, in FIG. 3 also, the gains of the power amplifiers 10 and 17 are interlocked, and for
example, when the gain of the power amplifier 10 is doubled, the gain of the power amplifier 17
is doubled.
[0033]
Also, in either case of FIG. 2 or FIG. 3, in order to set the frequency characteristic of the
reproduction signal to a desired characteristic, an equalizer may be inserted in the front stage of
the A / D converter 7 or the A / D converter You may put a digital equalizer in the latter part of
7.
Also, an equalizer with the same characteristic may be inserted in the front stage of the power
amplifiers 10 and 17.
[0034]
FIG. 4 shows a speaker system of a sound reproducing apparatus according to a third
embodiment of the present invention.
The circuit of the third embodiment is the same as that shown in FIG.
In this example, the reproduction speaker 21 and the muffling speaker 22 are vertically disposed,
and the sound from the back surface of the reproduction speaker 21 is guided to the front
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surface of the muffling speaker 22, and an opening which is an outlet of the back sound. A
muffling speaker 22 is installed at 23 and the muffling speaker 22 is attached to a cabinet 24
formed of a closed box.
Further, a microphone 25 for error detection is disposed in the opening 23. The operation is as
described with reference to FIG.
[0035]
The reproduction speaker 21 and the muffling speaker 22 may be disposed laterally or obliquely.
By doing this, the degree of freedom in design is enhanced, and a variety of designs can be made.
[0036]
According to the sound reproducing apparatus of the present invention, the speaker unit for
reproduction is open on the rear surface, and there is no interference between the sound emitted
from the rear of the reproduction speaker unit and the sound emitted before. Since the sound
emitted from the rear is canceled by the muffling speaker unit, the reduction of the bass is
extremely reduced, and the disturbance of the characteristics is also reduced, so that it is possible
to obtain low-frequency characteristics close to the state of being placed in an infinite cabinet.
There is no distortion due to differences in air compliance before and after the speaker.
[0037]
In addition, low frequency characteristics can be improved by controlling so as not to mute only
the frequency at which the sound from the rear and the sound from the front intensify in phase.
At this time, by adjusting the length of the guide wall appropriately, any frequency can be
emphasized, so that the low range can be enhanced.
[0038]
Furthermore, by linking the gain of the power amplifier, the coefficients of the adaptive filter or
the FIR digital filter can be kept unchanged even when the volume is increased, and the gain of
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the power amplifier on the reproduction side is increased in order to increase the volume of
reproduced sound In this case, it is possible to prevent the overflow of the range of the D / A
converter on the noise reduction side which is the control system.
[0039]
Brief description of the drawings
[0040]
1 (a) is a front view showing a speaker system of a sound reproducing apparatus according to a
first embodiment of the present invention, FIG. 1 (b) is a sectional view showing the same
speaker system, and FIG. It is sectional drawing which shows the modification of a speaker
system.
[0041]
2 is a circuit diagram of the same sound reproduction apparatus.
[0042]
3 is a circuit diagram of a sound reproduction apparatus according to a second embodiment of
the present invention.
[0043]
4 is a cross-sectional view showing a speaker system of the sound reproduction apparatus
according to the third embodiment of the present invention.
[0044]
5 is a side view showing an example of a speaker system of the conventional sound reproduction
apparatus.
[0045]
6 is a perspective view showing another example of the speaker system of the conventional
sound reproduction apparatus.
[0046]
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Explanation of sign
[0047]
DESCRIPTION OF SYMBOLS 1 speaker for reproduction 2 speaker for muffling 3 guide wall 4
cabinet 5 error microphone 6 reproduction device 7 A / D converter 8 adaptive filter 9 D / A
converter 10 power amplifier 11 FIR digital filter 12 control device 13 A / D converter 14 band
elimination filter 15 delay device 16 D / A converter 17 power amplifier 18 microphone
amplifier 19 FIR digital filter 21 speaker for reproduction 22 speaker for muffling 23 opening 24
cabinet 25 microphone for error detection 31 ducted cabinet 32 upper end face 33 Loudspeaker
34 Detection microphone 35 Lower end face 36 Silencer speaker 37 Monitor microphone
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