JPH03169199A - Active noise canceler - Google Patents

Abstract

PURPOSE:To improve performance in a low frequency area by providing a microphone for monitor at a position where sounds to be radiated from both loudspeakers are canceled each other. CONSTITUTION:On a partition wall 5, an air vent 5a to communication an intermediate space C with spaces B and D on both sides of the loudspeaker is bored and at the lower positions of both loudspeakers 1 and 2, an air vent 5b is bored to communication the spaces B and D on both sides of the loudspeaker. At a position on a symmetric surface A in the central part of the input hole 5b, a microphone fitting hole 5c is formed. A microphone 3 for monitor is installed at the microphone fitting hole 5c. Thus, at the microphone 3 for monitor, only external noise (c) is inputted and howling can be prevented from being generated by adding a source signal to a 360 deg. integer multiple feedback signal. Then, the silencing performance is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an active noise canceller having a function of actively canceling external noise.

(Prior Art) Conventionally, active noise cancellers such as those described in US Pat. No. 4,455,675 are known. This active noise canceller outputs a canceling sound that is in the opposite phase to the input sound from the monitoring microphone from a silencing speaker, and cancels the external noise by canceling the external noise and the canceling sound.

However, according to this conventional technique, there is a problem in that it is difficult to input the canceling sound evenly and to install a monitoring microphone so as not to disturb the sound field of the canceling sound.

Moreover, since the monitoring microphone needs to input external noise, it is necessary to provide a certain distance from the muffling speaker, which causes a problem of phase lag and howling.

Therefore, the applicant of the present application proposed an active noise canceller (hereinafter referred to as prior art) described in Japanese Patent Application No. 1-44790 as a means to solve the above conventional problems with a simple control circuit that does not require feedback control. ) was proposed.

In this prior art, a sub-speaker that emits a sub-cancelling sound having the same phase as the canceling sound is provided on the negative pressure side of the muffling speaker, and a monitoring microphone is provided at a position where the canceling sound and the sub-cancelling sound cancel each other out. I am trying to make sure that only external noise is input to the microphone.

However, this prior art does not take into account the wrap-around of low frequencies from the speaker, so low frequency sounds such as negative canceling sound, sub-cancelling sound, and negative sub-cancelling sound are transferred to the positive pressure side of the muffling speaker. There is a fear that the noise loops around and cancels out the sound in the low frequency range of the canceling sound, reducing the output of the canceling sound in the low frequency range, leading to a decrease in the silencing performance in the low frequency range.

By the way, in a speaker with a diameter of about 4 cm, the output drops rapidly in the frequency range of 300 Hz or less.

The present invention was made in view of the above-mentioned problems, and an object of the present invention is to develop an active noise canceller that makes it possible to improve silencing performance in a low frequency range.

(Means for Solving the Problems) In order to solve the above problems, the active noise canceller of the present invention includes a silencing speaker that emits a predetermined canceling sound from a positive pressure side, and a positive and negative side on the negative pressure side of the silencing speaker. A sub speaker provided with one side facing each other,
a monitor microphone disposed at a position where the sounds emitted from both speakers cancel each other out and inputting a person to be muted;
A canceling sound generation signal is outputted from the positive pressure side of the muffling speaker to emit a canceling sound having a phase opposite to that of the input sound of the monitoring microphone, and a sub-cancelling sound having the same phase as the canceling sound is emitted from one of the positive and negative sides of the sub-speaker. a noise canceling circuit that outputs a sub-cancelling sound generation signal to radiate noise, a noise canceling circuit that is provided on the outer periphery of both speakers, a silencing speaker side space on the positive pressure side of the silencing speaker, an intermediate space between both speakers, and a noise canceling circuit that is provided on the outer periphery of both speakers, A partition wall is provided which defines a positive and a negative sub-speaker side space.

(Function) The active noise canceller of the present invention is similar to the prior art in that the silencing speaker emits a canceling sound having a phase opposite to that of the person whose noise is to be silenced, and the noise is silenced by the canceling action.

By the way, in the case of the present invention, the silencing speaker side space, the intermediate space, and the sub speaker side space are defined by the partition wall.

The muffling speaker emits a canceling sound from the positive pressure surface to the muffling force side space, and simultaneously emits a negative canceling sound having an opposite phase to the canceling sound from the negative pressure surface to the intermediate space.

On the other hand, the sub-speaker emits a sub-cancellation sound with the same phase as the canceling sound from one side (positive and negative) to the intermediate space, and at the same time emits a sub-cancellation sound with the same phase as the cancellation sound from the other side into the sub-sub-force side space. emits a negative sub-cancellation sound.

Therefore, in the intermediate space, the negative canceling sound from the muffling speaker and the sub-cancelling sound from the sub-cancelling sound having the opposite phase are emitted, and a position where both sounds cancel each other out and become 0 is generated.

Similarly, between the muffling speaker side space where the canceling sound is emitted and the sub speaker side space where the negative sub canceling sound having the opposite phase is emitted, there is a position where the two sounds cancel each other out and become O.

In addition, in the present invention, since the monitor microphone is provided at a position where the sounds emitted from both speakers cancel each other out, the monitor microphone is not affected by the sounds emitted from both speakers. , it becomes possible to input only the person whose sound is to be muted.

Therefore, it is possible to prevent the occurrence of howling caused by the addition of the original signal and the feedback signal of an integral multiple of 360 degrees, and to improve the noise reduction performance.

In addition, since the monitor microphone only needs to be installed at a position where the sounds emitted from both speakers cancel each other out, as long as this condition is met, it is necessary to install the monitoring microphone at a position where the sound emitted from both speakers cancels out each other. It is also possible to arrange it close to the , and this also makes it possible to improve the silencing performance.

Moreover, the installation position of such a monitor microphone is
Since it will be installed at a position away from the radiation front of the positive pressure side of the muffling speaker, it will not disturb the sound field of the muffling subica, and this will improve the muffling performance, especially in the high frequency range with short wavelengths. .

Furthermore, in the present invention, the partition wall can block the low frequency components of the negative canceling sound, sub-cancelling sound, and negative sub-cancelling sound from entering the space on the muffling speaker side from which the canceling sound is emitted. can improve the silencing performance of

(Example) Hereinafter, an example of the present invention will be described based on the drawings. still,
In explaining the embodiment, a headphone-type device that is worn on the head and used by a person to cancel noise will be explained as an example. Also, the same reference numerals in each figure indicate the same objects.

First, the configuration will be explained.

FIG. 1 is an overall diagram showing the configuration of an active noise canceller according to a first embodiment of the present invention, and in the figure, 1
2 is a muffling speaker, 2 is a sub-speaker, 3 is a monitor microphone for inputting external noise, and 4 is a canceling sound generation signal sent to the muffler speaker 1 to generate a canceling sound having a phase substantially opposite to the input sound of the monitoring microphone. e, and at the same time outputs a sub-cancelling sound generation signal f to the sub-speaker 2 in order to generate a sub-cancelling sound with a phase opposite to that of the canceling sound (same phase as the input sound of the monitor microphone 3).
A noise canceling circuit 5 that outputs a noise canceling circuit 5 is a partition wall provided on the outer periphery of the muffling speaker 1 and the sub-speaker 2.

The muffled speaker 1 includes a housing la. It is composed of a diaphragm +b, a coil 1c, and a magnet 1d, with the front surface 1e of the diaphragm serving as a positive pressure surface and the back surface 1f of the diaphragm serving as a negative pressure surface. Note that a hole 19 for air venting is formed in the housing 1a.

The sub-speaker 2 is the same speaker as the muffling speaker 1, that is, an acoustically equivalent speaker, and is located in the housing 2a. Diaphragm 2b, coil 2c, magnet 2
d, and the housing 2a is provided to face the housing 2a of the silencer speaker 1 in a plane symmetrical manner, that is, the diaphragm back surface 1f, which is a negative pressure surface, and the diaphragm back surface 2f are provided to face each other. In addition, the dashed-dotted line A indicates both speaker forces 1,
2 shows the plane of symmetry. Further, in the sub speaker 2, the diaphragm surface 2e is a positive pressure surface, and the housing 2a
A hole 29 for air venting is formed in the.

By the way, the muffling speaker 1 is mounted facing the ear cavity E of the user when in use, and the space between both the speakers 1 and 2 as well as between the speakers 1.2 and the ear cavity E is so-called. It is covered with a cover 6 shaped like a headphone (see FIG. 5; only the inner surface is shown in FIG. 1).

Both speakers 1 and 2 are fixed to a partition wall 5, and supported by a cover 6 by the partition wall 5. a silencing speaker side space facing the diaphragm surface 1e of the speaker 1; an intermediate space C between the housings 1a and 2a between both the speakers 1 and 2; and a sub-speaker facing the diaphragm surface 2e of the sub-speaker 2. It is defined by a side space D.

The partition wall 5 is provided with an air vent hole 5a that communicates the intermediate space C with the speaker side spaces B, D, and the speaker side spaces B, D are connected to each other at a position below the speakers 1.2. An input hole 5b is formed to communicate with the input hole 5b, and a microphone mounting hole 5C is formed at the center of the input hole 5b at a position on the plane of symmetry A.

The monitor microphone 3 is attached to the microphone mounting hole 5c.
It is installed in

The noise canceling circuit 4 includes a monitoring microphone 3.
This circuit forms a cancellation sound generation signal e and a sub-cancellation sound generation signal f based on the input sound, and includes a pre-amplifier briambium 4a, a filter circuit 4b that removes an unnecessary frequency range from the cancellation sound, and a main circuit. It is formed to include a power amplifier 4c for amplification and an inversion circuit 4d for shifting the phase of input sound by 180 degrees.

For the muffling speaker 1, an inverting circuit 4d
A canceling sound generation signal e having a phase opposite to that of the input signal from the monitor microphone 3 is provided through the monitor microphone 3.

On the other hand, the sub-cancelling sound generation signal f having the same phase as the input signal from the monitor microphone 3 is given to the sub-speaker 2 without going through an inverting circuit. A sub-cancelling sound having the same phase as the canceling sound is emitted from the housing 2a, and this sub-cancelling sound is emitted to the back surface 1f of the diaphragm through the hole 29 of the housing 2a and the hole 19 of the housing 1a.

Next, the effect will be explained.

For example, when used under external noise such as inside the cockpit of an aircraft, the external noise passes through a cover (not shown) and is transmitted from the sub-speaker side space D or the muffled speaker side space into the input hole 5b, and is transmitted to the input hole 5b for the monitor. input to microphone 3.

The noise canceling circuit 4 generates a canceling sound generation signal e having a phase opposite to that of the input signal, and based on this signal e, a canceling sound is emitted from the silencing speaker 1 toward the user's ear cavity E, and the canceling sound is emitted from the silencing speaker 1 toward the user's ear cavity The external noise transmitted to E is canceled by the canceling sound a having the opposite phase and is muffled.

By the way, when the canceling sound a is emitted from the muffling speaker 1, the canceling sound a as shown in FIG. ) A negative canceling sound b having an opposite phase is emitted from 1f.

On the other hand, the sub-speaker 2 is given a signal with an opposite phase to that of the silencing speaker 1, that is, the sub-cancelling sound (a) having the same phase as the canceling sound a is emitted from the back surface 2f of the diaphragm, while the diaphragm surface A negative sub-cancellation sound (b) having a phase opposite to that of the sub-cancellation sound is emitted from 2e.

Therefore, on the symmetry plane A of both speakers 1 and 2, which is the position where the monitor microphone 3 is provided, there is a cancellation sound a from the diaphragm surface 1e of the muffler speaker 1, and a cancellation sound a from the diaphragm surface 2e of the sub-speaker 2. The negative sub-cancellation sound (b) is transmitted equally, and the rain sound cancels each other out to become O.

Therefore, only the external noise C (Fig. 2) is input to the monitor microphone 3, which prevents howling caused by adding the original signal and the feedback signal that is an integer multiple of 360 degrees. Therefore, it is possible to prevent the deterioration of the silencing performance due to the occurrence of howling.

Moreover, the monitor microphone 3 has a diaphragm 1b.
Because it is placed on the side, away from the front surface of the emission of canceled sound a from the silencing speaker 1, the sound field of the silencing speaker 1 is not disturbed, so stable silencing performance can be obtained up to the high frequency range.

Furthermore, since the partition wall 5 defines the silencing speaker side space, the intermediate space C, and the sub-speaker side space D,
Negative cancellation sound b emitted from the back surface 1f of the diaphragm
Also, low frequency sounds such as the sub-cancelling sound (a) emitted from the diaphragm back surface 2f and the negative sub-cancelling sound (b) emitted from the diaphragm surface 2e go around to the silencing force side space B, respectively. There is no. Therefore, the output of the canceling sound a in the low frequency range does not decrease due to the canceling effect caused by the wraparound of the sound in the low frequency range, and stable sound silencing performance can be obtained up to the low frequency range. In addition, in the intermediate space C, the back surface 1 of the diaphragm
The negative canceling sound b emitted from f is canceled by the sub-cancelling sound (a) emitted from the back surface 2f of the diaphragm.

Furthermore, since the monitoring microphone 3 is installed in the input hole 5b near the sides of both speakers 1 and 2, it is possible to input only the same external noise that is transmitted to the ear cavity E of the user. . Therefore, stable noise reduction performance can be obtained, and a feedback control circuit or microphone is not required, making the construction simple.

Furthermore, in this embodiment, the same speaker as the muffling speaker 1 is used as the sub-speaker 2 for canceling the negative canceling sound b emitted from the back surface 1f of the diaphragm of the muffling speaker 1, so that the sub-speaker 1 is acoustically equivalent, so that sub-cancellation occurs. As the signal f, the input signal from the motor microphone 3 can be used as is, and there is no need to vary the output with respect to the canceling sound generation signal e, and the configuration can be simplified.

Furthermore, in the embodiment, since the partition wall 5 is also used as a support member for both speakers 1 and 2, a support member is not required.
This also simplifies the configuration.

Next, a second embodiment of the present invention shown in FIG. 3 will be described.

In this embodiment, a microphone mounting hole 25c is formed in an intermediate space C, a monitoring microphone 3 is installed so as to input the sound in the intermediate space C, and a microphone mounting hole 25c is installed in each of the spaces B and C of the partition wall 25. ．． This is an example in which a sound absorbing material 25h is attached to a position facing D. Note that 25a is an air vent hole.

Therefore, in the case of the second embodiment, the monitor microphone 3 inputs the external sound that has entered the intermediate space C from the muffling speaker side space B or the sub-speaker side space D, passing through both the speakers 1 and 2. Note that the sounds emitted from the rear surfaces if and 2f of the diaphragms of both speakers 1 and 2 have opposite phases, so they cancel each other out and are not input to the monitor microphone 3.

In addition, since sound is absorbed by the sound absorbing material 25h, diffuse reflection of external sound and sound emitted from both speakers 1 and 2 is suppressed, and sound deadening performance is improved.

Next, a third embodiment shown in FIG. 4 will be described.

This third embodiment has a muffling speaker 31 and a sub-sounding force 32.
This is an example of sharing a magnet with

That is, the magnet 30 is supported by the rod 37 and is disposed at the center of the intermediate space C. A diaphragm 1b and a diaphragm 2b are provided symmetrically with the magnet 30 in between.

Therefore, sound is emitted based on the attraction between the magnetic field generated by energizing the coils lc and 2c and the magnet 30.

In this way, by sharing the magnet 30 in this embodiment, both the diaphragms lb,
By narrowing the interval between 2b, compactness can be achieved.

Next, a fourth embodiment shown in FIG. 5 will be described.

In the figure, 6 is a cover, which is formed into a bowl shape,
A pad 6a is provided on the periphery, and a sound hole 6b with a grill is formed on the bottom of the bowl (right end in the figure).

The inside of the cover 6 is partitioned by a partition wall 45 into a silencing power side space and a sub-speaker side space D.

A sound absorbing material 45 is provided on the surface of the partition wall 45 and the inner surface of the cover 6.
h. 6c is attached.

Further, the monitor microphone 3 is attached facing the intermediate space C.

Note that the other configurations are the same as those in the third embodiment, so explanations will be omitted.

Therefore, in this fourth embodiment, external sounds such as noise mainly enter the sub-speaker side space D through the sound hole 6b, pass through both speakers 31 and 32, and try to reach the ear cavity E. The external sound is canceled by the canceling sound emitted from the muffling speaker 31.

In this case, in the space on the muffling speaker side, the sound absorbing materials 45h and 6c provided on the surface of the partition wall 45 and the inner surface of the cover 6 suppress the diffused reflection of the canceling sound emitted from the muffling speaker 31 and the external sound, thereby improving the sound muffling performance. improves.

Further, in the sub-speaker side space D, the negative sub-cancelling sound emitted from the sub-speaker 32 is suppressed from being reflected inward on the inner surface of the cover 6.

Although the embodiment has been described above based on the drawings, the specific configuration is not limited to this embodiment, and even if there is a design change within the scope of the gist of the present invention, it is included in the present invention. .

For example, in the embodiment, a headphone-type device that is worn on the head and used by a person to remove external noise is shown as an example, but the scope of application of the present invention is not limited to this. - It may be installed indoors in ships, aircraft, factories, houses, etc., and used to cancel indoor noise, etc., or to cancel mechanical noise from vehicle air conditioners and other industrial equipment. .

Furthermore, since the present invention is for canceling the person to be muted, the person to be muted is not limited to the above-mentioned noise, but for example, for the purpose of harmonizing the sounds, only arbitrary sounds can be canceled. It can also be used to cancel.

In addition, in the embodiment, an example was shown in which the partition wall was brought into contact with the cover to completely define the silencing speaker side space and the sub-speaker side space, but it is also possible to restrict the wraparound of low frequency sounds by a desired amount. If there is, it is not necessary to completely define both spaces, but only to partially define them at the outer peripheral positions of both speakers.

(Effects of the Invention) As explained above, the active noise canceller of the present invention is not affected by the sound emitted from both speakers, and it is possible to input only the person whose noise is to be muted. As a result, it is possible to obtain an effect that the sound deadening performance can be improved.

At the same time, it is now possible to place the monitor microphone close to the silencer speaker, which also allows for
It is possible to improve the silencing performance, and there is an effect that the structure can be simplified, since the structure of a feedback circuit or the like is not required.

Moreover, according to the present invention, the monitoring microphone does not disturb the sound field of the silencing speaker, and as a result, the silencing performance can be particularly improved in a high frequency range with a short wavelength.

In addition, in the present invention, the partition wall prevents negative canceling sound, sub-cancelling sound, and negative sub-cancelling sound from entering the space on the silencing speaker side, improving the low frequency range output of the canceling sound, and improving the low frequency range output of the canceling sound. The effect is that the silencing performance of the silencing system can be improved.

[Brief explanation of the drawing]

Fig. 1 is an overall diagram (partially omitted) showing the configuration of the active noise canceller according to the first embodiment of the present invention, and Fig. 2 shows the canceled sound of the silenced speaker and negative cancellation by the active noise canceller according to the first embodiment. A characteristic diagram showing sound and external noise. Fig. 3 is a cross-sectional view showing the main part configuration of the active noise canceller according to the second embodiment of the present invention. Fig. 4 shows the main parts of the active noise canceller according to the third embodiment of the present invention. FIG. 5 is a sectional view showing the main part structure of an active noise canceller according to a fourth embodiment of the present invention. 1 1 2 2 B...Muffling speaker side space C...Intermediate space D...Sub speaker side space a...Cancellation sound b...Sub cancellation sound 1...Muffling speaker power e... Diaphragm surface (positive pressure side) f... Back side of diaphragm (negative pressure side) 2... Sub speaker e - Diaphragm surface (positive pressure side) f... Back side of diaphragm (negative pressure side) 3... Monitor microphone 4.・・Noise canceling circuit 5 ・・Bulkhead 25 ・・Bulkhead 31 ・・One-silence speaker 32 ・・Sub-speaker 45 ・・Bulkhead

Claims (1)

[Claims] 1) A muffling speaker that emits a predetermined canceled sound from a positive pressure side; a sub-speaker provided on the negative pressure side of the muffling speaker with one of its positive and negative sides facing each other; and a sub-speaker that emits predetermined canceled sound from both speakers. A monitoring microphone is placed at a position where the sounds input to the monitor microphone cancel each other out and inputs the person to be silenced, and a canceling sound is generated to emit a canceling sound having an opposite phase to the input sound of the monitoring microphone from the positive pressure side of the silencer speaker. A noise canceling circuit that outputs a sub-cancelling sound generation signal in order to output a signal and emit a sub-cancelling sound having the same phase as the canceling sound from either the positive or negative side of the sub-speaker; A partition wall defining a silencing speaker side space on the positive pressure side of the speaker, an intermediate space between both speakers, and a sub speaker side space on the other side of the positive and negative sides of the sub speaker. Active noise canceller.