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DESCRIPTION JPH03274997

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DESCRIPTION JPH03274997
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
active noise canceller having a function of actively canceling external noise, and more
particularly to improvement of input / output characteristics. (Prior Art) Conventionally, as an
active noise canceler, for example, one as described in US Pat. No. 4,455,675 is known. The
active noise canceller outputs cancellation sound in the opposite phase to the input sound from
the monitoring microphone from the muffling speaker, and mutes external noise by canceling out
the external noise and the cancellation sound. However, according to this prior art, there is a
problem that it is difficult to install a monitoring microphone so as to input the cancellation
sound without bias and not to disturb the sound field of the cancellation sound. In addition, since
the monitor microphone needs to receive external noise as well, it needs to be spaced to a certain
extent from the muffling speaker, which causes a phase delay to cause howling. Therefore, the
applicant of the present invention has proposed an active noise canceller (hereinafter referred to
as "previous process" described in Japanese Patent Application No. 1-44790 as a means for
solving the above conventional problems with a simple control circuit which does not require
feedback control. Called technology). In this prior art, the negative pressure surface of the
muffling speaker is provided with a sub-speaker that emits a sub-cancelling sound in phase with
the canceling sound, and the sound in reverse phase to the canceling sound radiated from the
negative pressure surface of the muffling speaker The monitoring microphone is provided at a
position where the sub-canceling sound and the secondary cancellation sound cancel each other
so that only the external noise is input to the monitoring microphone. (Problems to be Solved by
the Invention) In the above-mentioned prior art, as the sound radiated from both speakers, the
whole range of the frequency can be muted so that the sound to be muted can be muted
uniformly. It is preferable that the output characteristic is flat and the output characteristic is
uniform, but it is difficult to obtain such an output characteristic. Therefore, it is desirable to
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improve characteristics so as to obtain flat output characteristics with a simple configuration.
Furthermore, when both speakers emit a sound, if the vibrating member such as the diaphragm
receives an external sound (a compressional wave) such as a reflected sound, for example, the
vibration state changes, and this also causes There is a problem that it is difficult to obtain the
flat characteristics as described above. Furthermore, although the above description is on the
output side, it is preferable that the input characteristic is flat so that the monitor microphone on
the input side can correctly input whatever sound the input sound is. Since this monitor
microphone also has a structure for inputting sound based on the vibration of the vibrating
member, flat input characteristics can not be obtained due to the influence of external sound as
described above.
Therefore, in this case as well, characteristic improvement is desired such that flat input
characteristics can be obtained with a simple configuration. The present invention has been made
focusing on the problems as described above, and it is the first development of an active noise
canceller capable of blocking external influences and improving the characteristics of output
characteristics with a simple configuration. The second problem is to develop an active noise
canceller that can block external influences and improve input characteristics with a simple
configuration. (Means for Solving the Problems) In the active noise canceller of the present
invention, the first problem is solved by covering the entire surfaces of both speakers with a
housing having pores, and a monitor with the same housing is used. The second problem is
solved by covering the microphone. That is, in the active noise canceller according to the first
aspect of the present invention, there is provided a noise reduction speaker for emitting a
predetermined cancellation sound from the positive pressure surface toward the noise reduction
target space, and the cancellation noise toward the negative pressure surface of the noise
reduction speaker. The sub-speaker that emits the sub-cancelling sound in phase with the sound,
the monitor microphone placed at the position where the sound radiated from both speakers
cancel each other, and the canceling sound of the phase opposite to the input sound from the
monitoring microphone The cancellation sound generation signal is output to cause the one side
of the muffling speaker to emit a cancellation sound generation signal, and the other cancellation
sound is generated from the sub speaker to the other side of the muffling speaker so as to emit a
cancellation sound in phase with the cancellation sound. And a noise cancellation circuit for
outputting the noise, and a plurality of noise suppression circuits covering the entire surface of
the muffling speaker and the sub-speaker, It provided a speaker housing which pores are formed.
In the active noise canceller according to the second aspect of the present invention, the
microphone housing is provided in place of the speaker housing so as to cover the entire surface
of the monitoring microphone and in which a plurality of pores are formed. (Operation) When
muffling is performed, the cancellation sound is emitted from the muffling speaker toward the
muffling target space based on the sound input from the monitoring microphone. Therefore, in
the noise reduction target space, the extraneous sound is canceled by the cancellation sound of
the opposite phase. Also, the monitoring microphone is disposed at a position where the sound
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from both speakers is canceled, that is, at this position, the cancellation sound emitted from the
positive and negative sides of the muffling speaker and the other side are emitted The
cancellation sound is a negative cancellation sound in the opposite phase to the cancellation
sound emitted from the positive or negative side of the sub-speaker, and the negative
cancellation sound in the opposite phase to the cancellation sound (negative-side canceler) The
sound from both speakers is not input, and only the external sound can be input.
Then, in the active noise canceller according to claim 1 of the present invention, the sound
radiated from both the speakers is output through the pores of the speaker housing. That is, the
radiation sound from both speakers receives resistance when passing through the pore.
Therefore, depending on the position of the highest diameter and the position of the pore and the
number of pores, it is possible to make it easy to pass or hard to pass the sound of a specific
frequency, ie, the output is too high in both speakers While making it difficult to pass sound in
the frequency range and making it easy to pass sound in the frequency range whose output is too
low, it is possible to obtain flat output characteristics. And the sound from the outside world such
as the reflection sound and the external sound also reaches the both speakers through the pores
of the speaker housing and receives resistance from passing through the pores and both
speakers receive from the outside world The impact is mitigated. Also, in the active noise
canceller according to claim 2, the extraneous sound passes through the pores of the microphone
housing and is input by the monitoring microphone. Therefore, also in this case, the sound of a
specific frequency can be easily made to pass or hard to pass depending on the diameter of the
pore and the position of the pore and the number of the pore, that is, in the monitoring
microphone A flat input characteristic can be obtained by making it difficult to pass sounds in
the frequency range where the input is too strong and passing sounds in the frequency range too
weak. An embodiment of the present invention will be described below with reference to the
drawings. In the description of the embodiments, the same reference numerals indicate the same
objects in the respective drawings. First, the configuration of the first embodiment corresponding
to the invention of claim 1 will be described. FIG. 1 is an overall view showing a configuration of
an active noise canceler according to a first embodiment of the present invention, in which 1 is a
noise reduction generating and emitting a predetermined cancellation sound to the user's ear
cavity E A speaker 2, a sub-speaker 2, 3a and 3b, a first monitor microphone and a second
monitor microphone for inputting the external sound A, a cancel sound generation signal a to the
muffling speaker 1, and a sub-speaker 2 A noise cancellation circuit that outputs a secondary
cancellation sound generation signal, 5 is a partition, and 6 is a cover. The muffling speaker 1 is
provided with a diaphragm 1b, a coil lc, and a magnet 1d. When the coil 1c is energized, it is
attracted to the magnet 1d to vibrate the diaphragm 1b. The diaphragm surface 1e is a positive
pressure surface. The back surface 1 f is a negative pressure surface.
The sub-speaker 2 is the same speaker as the muffling speaker 1, that is, an acoustically
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equivalent speaker including a diaphragm 2b, a coil 2c and a magnet 2d, and the diaphragm
surface 2e is a positive pressure surface, and the diaphragm The back surface 2f is a negative
pressure surface. The partition wall 5 defines the inside of the headphone-like cover 6 into a
muffling space B and an extraneous sound side space C, and supports both the speakers 1 and 2.
The support structure supports the two speakers 1.2 symmetrically at the center of the partition
5 and forms an intermediate chamber between the two speakers 1 and 2. Further, in the partition
wall 5, a communication hole 5a for communicating the intermediate chamber with the
extraneous sound side space C is formed. The two monitoring microphones 3a and 3b are
attached to mounting holes 5b formed in the partition wall 5 at a lower position between the two
speakers 1.2. That is, the two microphones 3a and 3b are integrally provided on the back to back
and are formed in a single directivity, and the directivity direction is parallel to the radiation
direction of the sound of both speakers 1.2. It is installed in the direction of the muffling space
and the extraneous sound side space C. The two microphones 3 a and 3 b and the two speakers 1
° 2 are connected to the noise cancellation circuit 4. That is, the noise cancellation circuit 4
radiates the cancellation sound s1 and the sub cancellation sound s2 from both the speakers 1.2
based on the sound input from both the microphones 3a and 3b, and the delay circuit 4a and the
gain circuit A preamplifier 4C, a filter circuit 4d, a power amplifier 4e and an inverting circuit 4f
are provided. The delay circuit 4a and the gain circuit 4b are connected to the first monitoring
microphone 3a, the delay circuit 4a delays the phase of the input signal from the first monitoring
microphone 3a, and the gain circuit 4b reduces the gain of the input signal. Change. In place of
the delay circuit 4a, a circuit for accelerating the phase may be provided. The preamplifier 4C
pre-amplifies the input signal from the first monitor microphone 3a and the input signal from the
second monitor microphone 3b which have passed through both circuits 4a and 4b, and includes
a gain circuit 4b and a second monitor microphone Connected to 3b. The filter circuit 4d is
configured to remove an unnecessary frequency range from the cancellation sound from the
signal passed through the preamplifier 4c, that is, to remove a sound in a frequency range which
can not be output from both the speakers 1 and 2. ing. The power amplifier 4e mainly amplifies
the signal that has passed through the filter circuit 4d so that the sound pressure of the
cancellation sound s1, which will be described later, becomes equal to the external sound A.
The inverting circuit 4 f is a circuit that shifts the phase of the signal from the power amplifier by
180 degrees and outputs it to the muffling speaker 1. By the way, the speaker housings 7.7 are
symmetrically provided so as to cover the entire surfaces of the diaphragm surfaces 1e and 2e of
the two speakers 1.2. Both speaker housings 7.7 are formed with a large number of pores 7a as
shown, and are formed in a curved shape as shown. The curved surface is shaped such that the
phase of the cancellation sound s1 emitted from the muffling speaker 1 matches in the ear cavity
E. That is, since the distance between the diaphragm 1b and the ear cavity E is short in the
illustrated use state, the influence of the distance difference is large. That is, in the diaphragm 1b,
the phase of the sound emitted from the portion near the ear cavity E and the sound emitted
from the far portion are easily shifted. Therefore, in the present embodiment, the curved surface
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of the speaker housing 7 is formed in a shape corresponding to the sound pressure distribution
characteristic of both the speakers 1.2, and many pores 7a are provided at positions away from
the ear cavity E, Resistance is given to the sound emitted near the ear cavity E so that the phase
is delayed. Next, the operation will be described. For example, when it is desired to prevent the
external noise from being heard under the external noise such as inside the cockbit of an aircraft,
the apparatus of the present embodiment is applied to the ear cavity E as shown in the drawing.
The operation at this time will be briefly described. First, external sound (external noise) A is
input from both microphones 3a and 3b. Then, the noise cancellation circuit 4 performs
predetermined delay / gain processing on the input signals from both the microphones 3 a and 3
b and also performs amplification / filter processing, and the phase of the muffling speaker 1
with the extraneous sound A. A cancellation sound generation signal a, which is a signal obtained
by reversing the above, is output, while a sub cancellation sound generation signal that is a signal
in the same phase as the extraneous sound A is output to the sub-speaker 2. Therefore, from the
muffling speaker 1, the cancellation sound s1 in the opposite phase to the extraneous sound A is
emitted toward the muffling space B, and in the muffling space B, the extraneous sound A cancels
the canceling action by the cancellation sound S1 in this antiphase. Received and muted. By the
way, when the cancellation sound S1 is emitted from the muffling speaker 1, a negative
cancellation sound t1 having a phase opposite to that of the cancellation sound s1 is emitted
from the diaphragm back surface 1f which is the negative pressure surface. On the other hand,
the sub-speaker 2 is supplied with a sub-cancel sound generation signal in reverse phase to the
cancel sound generation signal a, that is, from the diaphragm back surface 2 f toward the
muffling speaker 1 The cancellation sound s2 is emitted, and the negative cancellation table t2 (=
negative cancellation sound t1) having a phase opposite to that of the auxiliary cancellation
sound s1 (= cancellation sound s2) is emitted from the diaphragm surface 2e toward the
extraneous sound side space C. Ru.
Therefore, between the two speakers 1 and 2, that is, at the center position of the partition 5, the
negative cancellation sound t1 emitted from the muffling speaker 1 and the auxiliary cancellation
sound S2 emitted from the auxiliary speaker 2 have opposite phases. It is canceled and the
cancellation sound s1 from the muffling speaker 1 and the negative side cancellation stand t2
from the sub-speaker 2 are canceled because they are in opposite phase, and in this part, the
sound from both speakers 1.2 is input. Instead, only the external sound A can be input. The
active noise canceller of this embodiment mutes the extraneous sound A in this way, but the
sound radiated from both the speakers 1.2, although having a frequency range, vibrates the
speaker housing 7 Also, those in a certain frequency range are emitted to the muffling space B
and the extraneous sound side space C through the pores 7 a of the speaker housing 7.
Therefore, the radiation sound of both speakers 1.2 receives resistance according to the
frequency range by the speaker housing 7, whereby the characteristics when actually radiated to
the rain spaces B and D are radiation from the diaphragms lb and 2b. The characteristic is
different from the characteristic immediately after being subjected, and the characteristic can be
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arbitrarily changed depending on the diameter, the number and the position of the pore 7a, and a
flat output characteristic can be obtained. Further, in the case of the embodiment, based on the
curved surface shape of the speaker housing 7 and the position of the pores 7a, the phase
deviation in the ear cavity E does not occur. As described above, the speaker housing 7 of the
present embodiment not only affects the sound radiated from both the speakers 1 and 2 but also
affects the sound coming from the outside to the speaker 1.2 side. That is, the sound radiated
from both the speakers 1 and 2 is reflected to the both speakers 1.2 in the cover 6 and the ear
cavity E of the user. Also, the extraneous sound A also reaches the position of both speakers 1.2.
Thus, when sound comes to both the speakers 1 and 2, this sound is also a compression wave of
air, which adversely affects the vibration of the diaphragms 1b and 2b. On the other hand, in the
present embodiment, the speaker housing 7 serves as a resistance for the arrival of the reflected
sound and the extraneous sound A, and these adverse effects of the two speakers 1.2 are
alleviated. Further, in the present embodiment, when the balance of the sound outputted from
both the speakers 1 and 2 is not well-balanced at the positions of both the monitoring
microphones 3a and 3b, the delay circuit 48 and the gain circuit 4b are used. This imbalance can
be eliminated by shifting the phase of the signal input from the first monitoring microphone 3a
or changing the gain.
Next, a second embodiment of the present invention shown in FIG. 2 will be described. The
second embodiment corresponds to the inventions of claims 1 and 2 and is provided with a
single monitor microphone 23 and a housing 27 ° 27 covering both the speakers 1.2 and the
monitor microphone 23. Is an example in which A large number of pores 27 a are formed in the
housing 27. In the case of this embodiment, the configuration of the noise cancellation circuit 4
is different from that of the first embodiment, and the signal from the monitor microphone 23 is
inputted to the preamplifier 4c, and the delay circuit 4a and the gain shown in the first
embodiment. The circuit 4b will be omitted. Such a noise cancellation circuit is also shown in the
prior application (Japanese Patent Application No. 1-44790), so illustration is omitted. Further, in
this embodiment, the monitor microphone 23 is supported with the elastic member 20
interposed. In the case of this second embodiment, in addition to being able to arbitrarily change
the output characteristics of both speakers 1 and 2 as in the first embodiment, it is possible to
mitigate the adverse effect of outsiders on both speakers 1 and 2 The sound input to the
monitoring microphone 23 also receives resistance in the housing 27 and the pore 27a, and the
characteristic changes, and the characteristic change is arbitrarily made according to the shape
of the housing 27 and the diameter, number, and position of the pore 27a. It can be carried out.
Therefore, particularly, high frequency components can be cut to prevent howling. Also, howling
can be prevented by relaxing the vibration of the bulkhead 5 being input to the monitoring
microphone 23 by the elastic member 20. Next, a third embodiment shown in FIG. 3 will be
described. This embodiment is an example in which the housing 37 for covering both the
speakers is formed separately into a speaker housing 37a for covering both the speakers 1 and 2
and a microphone housing 37b for covering the monitoring microphone 23. And the pore 37c is
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formed in both part 37a, 37b. The operation is the same as that of the second embodiment, so
the description will be omitted. Next, a fourth embodiment shown in FIG. 4 will be described. This
fourth embodiment is an embodiment corresponding only to claim 2, wherein the monitor
microphone 23 is disposed in the recess 45 formed in the partition wall 5 so as to face the
intermediate chamber, and the monitor microphone 23 The microphone housing 47 is provided
to cover only the recess 45 so as to cover the In addition, 47a is a pore. Therefore, the
characteristics of the extraneous sound A can be arbitrarily changed before being input to the
monitoring microphone 23.
Next, a fifth embodiment shown in FIG. 5 will be described. This embodiment is an example in
which a microphone housing 57 having a pore 57 a is provided to cover the mounting hole 5 b
so as to cover the monitoring microphone 23. Therefore, the same operation as the fourth
embodiment can be obtained. Although the embodiment has been described above based on the
drawings, the specific configuration is not limited to this embodiment, and the present invention
cancels the sound to be silenced. The noise is not limited to the noise as described above, and for
example, there is also a usage power of canceling only an arbitrary sound for the purpose of
harmonizing the sound. In the example, the positive pressure surfaces 1e and 2e of the
diaphragms 1b and 2b of both speakers 1.2 are arranged toward the noise reduction target space
B and the external sound side space C, however, the negative pressure surface is rotated by 1800
degrees. If and 2f may be directed to that direction. (Effects of the Invention) As described above,
in the active noise canceller according to claim 1, a speaker housing is provided covering the
entire surface of the muffling speaker and the sub-speaker, and a plurality of the speaker
housings are provided. Since the configuration is such that the pores are formed, the output
characteristics of both speakers can be arbitrarily changed according to the diameter, number
and position of the pores, whereby it is possible to obtain flat output characteristics and a simple
configuration Thus, the effect that the output characteristics can be improved can be obtained.
Further, in the active noise canceller according to the second aspect of the present invention, the
microphone housing is provided to cover the entire surface of the monitoring microphone, and a
plurality of pores are formed in the microphone housing. The input characteristics of the
monitoring microphone can be arbitrarily changed according to the diameter, the number, and
the position of the sensor, thereby making it possible to obtain flat input characteristics and
improve the input characteristics by simple characteristics. The effect is obtained.
[0002]
Brief description of the drawings
[0003]
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FIG. 1 is a general view showing the structure of an active noise canceller according to a first
embodiment of the present invention, FIG. 2 is a cross sectional view showing the main part of
the second embodiment, and FIG. 3 is a third embodiment. FIG. 4 is a sectional view showing an
essential part of the fourth embodiment, and FIG. 5 is a sectional view showing an essential part
of the fifth embodiment.
1: Mute speaker 1e: Diaphragm surface (positive pressure surface) 1f: Diaphragm back surface
(negative pressure surface) 2: Secondary speaker 3a: First monitor microphone 3b: Second
monitor microphone 23 Monitor microphone 4 noise cancellation circuit 7 speaker housing 7a
pore 27 housing (speaker housing, microphone housing) 27a pore 37 housing ( Speaker housing,
microphone housing) 37c ... pore 47 ... microphone housing 47a ... pore 57 ... microphone
housing 57a ... pore a ... cancellation sound generation signal b ... secondary cancellation Sound
generation signal sl · · · cancellation sound s 2 · · · secondary cancellation sound
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