JP2786284B2 - Active noise canceller - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an active noise canceller having a function of actively canceling a sound to be silenced such as external noise.

2. Description of the Related Art Conventionally, as an active noise canceller, for example, one described in US Pat. No. 4,455,675 is known. The active noise canceller outputs a cancel sound having a phase opposite to that of the input sound from the monitoring microphone from a muffling speaker, and cancels the external noise by canceling the external noise and the cancel sound.

However, according to this conventional technique, there is a problem that it is difficult to input a cancel sound without bias and to install a monitoring microphone so as not to disturb the sound field of the cancel sound. In addition, the monitoring microphone needs to be provided with a certain distance from the muffling speaker because it is necessary to input external noise, which causes a problem that a phase delay occurs and howling occurs.

Therefore, the applicant of the present application has solved the above conventional problems,
Means for solving the problem by a simple control circuit that does not require feedback control are disclosed in Japanese Patent Application Nos. 1-44789 (hereinafter referred to as "first prior art") and Japanese Patent Application No. 1-444790 (hereinafter referred to as "second prior art"). Proposed a noise canceller.

In the first prior art, the monitoring microphone is disposed at a side position of the muffling speaker, where the cancellation sound radiated from the positive pressure surface and the negative cancellation sound radiated from the negative pressure surface of the muffling speaker cancel each other. Things.

On the other hand, the second prior art provides a sub-speaker that emits a sub-cancel sound in phase with the cancel sound on the negative pressure surface of the muffling speaker, and provides a monitoring microphone at a position where the cancel sound and the sub-cancel sound cancel each other out. Only external noise is input to the monitoring microphone.

(Problems to be Solved by the Invention) However, in the above-mentioned first prior art, since the front side and the back side of the sound deadening speaker are not symmetrical, the casing sound and the negative cancellation sound are symmetrical. There is a problem that it is difficult to find a position where radiation is not emitted and the two cancel each other, and that the position may be shifted depending on the frequency range.

On the other hand, according to the second prior art, since two speakers, a muffling speaker and a sub-speaker, are used, the position where the sound from both speakers cancel each other can be easily found, and the position is shifted depending on the frequency range. There's nothing wrong. Incidentally, if both speakers are acoustically equivalent speakers, the installation position of the monitor microphone is an intermediate position between the two speakers.

However, since the second prior art has two speakers, a muffling speaker and a sub speaker,
There is a problem that the device becomes large. Further, since the vibration members of the respective speakers are arranged with a distance therebetween, the sound absorbing performance is degraded due to the displacement of the sound pressure surface due to the distance, or the sound absorbing performance is reduced due to interference of sound from the sub-speaker. There was a problem of lowering.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and has as its object to develop an active noise canceller capable of simultaneously achieving compactness and improved noise reduction performance.

(Means for Solving the Problems) In order to solve the above problems, an active noise canceller according to the present invention employs a muffling speaker based on a cancellation sound generation signal output from a noise cancellation circuit based on an input sound from a monitoring microphone. In the active noise canceller, which emits a cancellation sound having a phase opposite to that of the sound to be muffled from the muffler to the muffling space, the muffling speaker has a vibration member that radiates the cancellation sound has a phase opposite to that of the surface on the cancellation sound emission side. The back side that emits the negative cancellation sound is formed in a symmetrical shape, and a coil provided on the vibrating member and a magnet that attracts or repels are provided on at least one of the front side position and the back side position of the vibrating member. The monitoring microphone is provided on an extension of the vibrating member.

(Operation) When erasing the sound to be silenced in the silencing space, first, input an extraneous sound including the sound to be silenced from the monitoring microphone, and the noise canceling circuit uses the input sound to generate a cancellation sound generation signal (electric signal). Is output.

The cancel sound generation signal generates a magnetic field in the coil of the muffling speaker, and the vibrating member vibrates by attracting or repelling to a magnet provided at least at one of the front surface position and the back surface position of the vibrating member. A cancellation sound having a phase opposite to that of the sound to be silenced is radiated from the surface side to the silencing space. The sound to be silenced is erased by the canceling action of the cancel sound.

In this case, when the magnet is provided on both surfaces of the vibration member, the sound pressure of the cancel sound is higher than when only one is provided.

In the vibration member, at the same time as the cancel sound is emitted from the front side as described above, a negative cancel cell sound having the opposite phase to the cancel sound is emitted from the back side symmetrically. As described above, the cancel sound and the negative cancel sound are input simultaneously with the input of the external sound including the sound to be silenced. However, since the installation position of the monitoring microphone is on the extension of the vibration member, this position is set. In this case, the cancel sound and the negative cancel sound are acoustically equivalently transmitted, and the two cancel each other out, so that only the visitor including the sound to be silenced is input.

Since the monitoring microphone can input the external sound including the sound to be silenced at the side of the silence speaker without being affected by the cancel sound radiated from the silence speaker, the above-described two prior arts can be used. Similar to the technology, howling can be prevented to improve the sound deadening performance, and the monitoring microphone can be arranged close to the sound deadening speaker to improve the sound deadening performance. By installing the vibration member at a position separated from the radiation front of the positive pressure surface of the vibration member, the noise reduction performance in a high frequency range can be improved.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.
In describing the embodiments, a headphone type device used by a person to be worn on the head and used to cancel noise will be described as an example. Further, in each drawing, the same reference numeral indicates the same object.

 First, the configuration will be described.

FIG. 1 is an overall view showing a configuration of an active noise canceller according to a first embodiment of the present invention.
Reference numeral 1 denotes a muffling speaker, 3 denotes a monitoring microphone, 4 denotes a noise canceling circuit, 5 denotes a support member, and 6 denotes a cover.

The muffling speaker 1 is for emitting a cancellation sound toward a muffling space B, and includes a housing 1.
a, a diaphragm 1b, a coil 1c, and magnets 1j and 1k. That is, as shown, the housing 1a
It has a shape like a combination of two bowls, and one diaphragm 1b is supported in the space inside the bowl. Also,
The housing 1a is provided with a plurality of air vent holes 1g.

The diaphragm 1b has a diaphragm surface 1e and a diaphragm surface 2f.
Is a diaphragm back surface 1f, and both surfaces 1e and 1f are formed in a symmetric, substantially disk shape. And this diaphragm 1b
When the coil 1c is energized, the diaphragm 1b moves to the left in the figure, and according to the amount of movement, the canceling sound a is emitted from the front surface 1e of the diaphragm and the diaphragm back surface
1f, a negative cancel sound b having a phase opposite to that of the cancel sound a is generated.
As for k, the polarity on the diaphragm side is the same, one is attracted to the coil 1c, and the other is repelled.

The above-mentioned muffling speaker 1 is mounted so as to face the ear cavity E of the user in use, and the muffling speaker 1 has a cover 6 in the form of a so-called headphone.
The cover 6 is covered with a plate-shaped support member 5.
It is fixed at.

Therefore, the space inside the cover 6 is defined by the support member 5 into a sound deadening space B on the diaphragm front surface 1e side of the sound deadening speaker 1 and an external sound side space D on the diaphragm back surface 1f side. The extraneous sound space D is covered by the cover 6.
An external sound, that is, an external sound c, is transmitted from an opening (not shown) formed in the above.

The monitoring microphone 3 is for inputting an external sound c including a noise target sound, and a communication hole 5a formed in the lower part of the support member 5 in the figure so as to communicate the two spaces B and D. At a position on the extension of the diaphragm 1b.

The noise canceling circuit 4 emits a cancellation sound having a substantially opposite phase to the input sound of the monitoring microphone 3 from the diaphragm surface 1e of the muffling speaker 1 to the muffling space B based on the input sound of the monitoring microphone 3. The noise canceling circuit 4 outputs a canceling sound generation signal e. The noise canceling circuit 4 includes a preamplifier 4a for pre-amplifying an input signal from the monitoring microphone 3, as shown in FIG.
It is formed to include a filter circuit 4b for removing an unnecessary frequency range from the cancellation sound, a power amplifier 4c for main amplification, and an inversion circuit 4d for shifting the phase of the input sound by 180 degrees.

That is, a signal having a phase opposite to that of the input sound is output to the coil 1c. In this embodiment, the magnet
When the polarities of 1j and 1k are reversed from those in the embodiment, the diaphragm 1b
Since the moving direction is reversed, the inverting circuit 4d becomes unnecessary, and the signal from the power amplifier 4c may be directly output to the coil 1c.

 Next, the operation will be described.

(A) At the time of manufacturing In this embodiment, the monitoring microphone 3 emits the cancel sound a emitted from the diaphragm surface 1e and the diaphragm back surface 1f that is acoustically equivalent to the cancel and has the opposite phase. Although it must be arranged at a position where the negative cancel sound b cancels out, this diaphragm 1b is substantially disc-shaped and has a symmetrical shape on the front and back surfaces 1e and 1f of the diaphragm.
At any position, both sounds a and b cancel each other regardless of the frequency.

 Therefore, it is easy to determine the setting position.

In addition, since only one mute speaker 1 needs to be provided as a speaker, the entire apparatus can be made compact.

(B) At the time of use The active noise canceller of the present embodiment is used by applying it to the ear cavity E as shown in the figure under external noise such as in the cockpit of an aircraft, for example. Also,
In this embodiment, a case will be described in which all the foreigners c are noises and all the foreign sounds c are removed.

In this case, the external sound (external noise) c is input to the monitoring microphone 3 from the external sound side space D or the silencing space B after passing through the cover 6.

In the noise canceling circuit 4, a canceling sound generation signal e is formed and output based on the input sound of the monitoring microphone 3, and based on the signal e, the canceling sound is generated from the diaphragm surface 1e of the muffling speaker 1 toward the ear cavity E of the user. a
Is radiated, and the visitor c in the sound deadening space B is canceled by the canceling effect of the cancel sound a having the opposite phase to the sound c. Also, in this case, since the magnets 1j and 1k are provided on both front and back sides of the diaphragm 1b, the amount of movement of the diaphragm 1b with respect to energization of the coil 1c is much larger than in the case of one coil, and the sound of the casing sound a The pressure is increased and the silencing performance is improved.

By the way, when the cancellation sound a is emitted from the muffling speaker 1, the cancellation a as shown in FIG. 2 is emitted from the diaphragm surface 1e of the muffling speaker 1, and the cancellation sound a is emitted from the diaphragm back surface 1f. A negative cancellation sound b having an opposite phase is emitted.

Therefore, at the position where the monitoring microphone 3 is provided, that is, the position on the extension of the diaphragm 1b, the two sounds b,
a is transmitted equivalently, and both sounds a and b cancel each other to become 0.

Therefore, the monitoring microphone 3 has a muffling speaker.
Only the external sound c is input without inputting the sound from the first and second sounds. By inputting the target sound exactly as described above, the noise reduction performance is improved, and the output from the noise reduction speaker 1 is improved. And how to generate a feedback sound that is an integral multiple of 360 ° can be prevented from being generated, which also has the effect of improving the silencing performance.

In addition, the monitoring microphone 3 is connected to the diaphragm 1b.
It does not hinder the emission of the cancel sound a from the loudspeaker, provides a stable noise reduction performance up to the high frequency range, and is installed at a position close to the ear cavity E, so that almost the same sound as the external sound c reaching the ear cavity E Can be input, and the silencing performance is high.

Further, the second prior art has two speakers, so that there is a problem of a decrease in sound pressure as described below. However, in the present invention, since there is only one muffling speaker 1, this problem does not occur. .

That is, if between the two loudspeakers diaphragm has a distance l, there is deviation in sound pressure surface due to the distance l, against silencing space from both _{^{speakers, - = 0 - + 0 -}} e jkl becomes sound Is output.

In addition, ^- : sound pressure effective value radiated to the left from one speaker, k; frequency (= 2πf / c), l; distance between diaphragms (vibrating members).

Therefore, when kl = nπ (n; a positive integer), no sound is output. For l = 1cm and c = 340m / s, f ₀ = 17kHz
Is the frequency with no output first.

Also, from P = 2P ₀ when k = 0, the frequency at which the 3 dB output decreases is −3 = 20 log {(1 + cos (2πfl / c) P ₀ / 2P ₀ }, and this frequency is approximately 6.2 kHz. Exists.

As described above, if the diaphragm has the distance l, the sound pressure decreases in a high frequency range, and the frequency decreases as the distance l increases. Therefore, the distance l is preferably smaller.

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

The second embodiment is an example in which both magnets 21j and 21k are formed in a donut shape. In this case, the transmission of the external sound c to the sound deadening space B and the emission of the cancel sound a
Not disturbed by 21j, 21k.

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

In this embodiment, the two magnets 31j and 31k are connected to the diaphragm 1
This is an example in which a large size is formed so as to have substantially the same diameter as b, and a large number of sound transmission holes 31m and 31n are formed in the magnets 31j and 31k.

In the case of the third embodiment, similarly to the second embodiment, the transmission of the extraneous sound c and the cancel sound a is good, and the magnetic forces of the magenets 31j and 31k are strong, and the sound pressure of the cancel sound a is high.

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

In this embodiment, the housing is divided into a front housing 41 and a rear housing 42, and a diaphragm 43 is provided with a coil installation portion 43a in which the coil 1c is installed, and two housings 41 from the outer peripheral end of the coil installation portion 43a. In this example, bellows-like expansion and contraction portions 43b and 43c are formed on the outer peripheral ends of the outer circumferences, respectively.

In the case of the fourth embodiment, the amount of movement of the coil installation portion 43a of the diaphragm 43 is increased, so that a cancel sound having a higher sound pressure can be emitted.

As described above, the embodiments have been described based on the drawings. However, the specific configuration is not limited to the embodiments, and even if there is a design change or the like without departing from the gist of the present invention, it is included in the present invention. .

For example, in the embodiment, a headphone type used by a person to be worn on the head to remove external noise has been described as an example, but the scope of the present invention is not limited to this.・ Installed in ships, aircraft, factories, houses, etc. to cancel indoor noise, etc.
It may be used to cancel mechanical noise of an air conditioner or other industrial equipment of a vehicle.

Further, since the present invention cancels the sound to be silenced, the sound to be silenced is not limited to the above-described noise.For example, for the purpose of harmonizing sounds, only an arbitrary sound may be used. There are also uses such as canceling.

(Effects of the Invention) As described above, in the active noise canceller of the present invention, a monitoring microphone is provided at a position where the cancel sound and the negative cancel sound cancel each other out, as in the prior art. Since only an outsider including the sound to be silenced can be input, howling can be prevented, and the microphone for monitoring can be arranged close to the silencer at a position off the radiation front of the cancel sound, thereby improving the silencing performance. The effect that it can be obtained is obtained.

In addition, according to the present invention, since the configuration is such that only the sound deadening speaker and no auxiliary speaker are provided, it is possible to reduce the size of the device, and to reduce the sound deadening performance due to interference due to sounds other than the cancellation sound and a deviation of the sound pressure surface. Is obtained. In addition, since the speaker can be made a single muffling speaker and compactness and muffling performance can be improved, since the front and back surfaces of the vibrating member are formed in a symmetrical shape, the canceling sound and the negative canceling sound are canceled out. It is easy to find a matching position, and at this position, the effect is obtained that the characteristics do not change depending on the frequency range.

[Brief description of the drawings]

FIG. 1 is an overall view showing the configuration of an active noise canceller according to a first embodiment of the present invention, and FIG. 2 is a characteristic diagram showing a cancel sound, a negative cancel sound, and external noise caused by the active noise canceller of the first embodiment. FIG. 3 is a sectional view showing a main part of an active noise canceller according to a second embodiment of the present invention. FIG. 4 is a sectional view showing a main part of the active noise canceller according to the third embodiment of the present invention. FIG. 5 is a sectional view showing a main part of an active noise canceller according to a fourth embodiment of the present invention. B: Silencing space a: Canceling sound b: Negative canceling sound 1: Silencing speaker 1b: Diaphragm (vibrating member) 1e: Diaphragm surface (vibrating member surface) 1f: Diaphragm back surface (vibrating member back surface) 1j … Magnet 1k …… Magnet 3 …… Monitor microphone 4 …… Noise cancellation circuit 21j …… Magnet 21k …… Magnet 31j …… Magnet 31k …… Magnet

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04R 3/00 H04R 3/02 G10K 11/16

Claims (1)

(57) [Claims] An active noise canceller which emits a canceling sound having a phase opposite to that of a sound to be canceled from a silencing speaker to a silencing space by a canceling sound generation signal output from a noise canceling circuit based on an input sound from a monitoring microphone. In the canceller, in the muffling speaker, a vibration member that emits a cancel sound is formed in a symmetrical shape with a front surface side on the cancel sound emission side and a back surface side that emits a negative cancel sound having a phase opposite to that of the cancel member. A coil provided on the vibrating member and a magnet for attracting or repelling are provided on at least one of the front side position and the back side position, and a monitoring microphone is provided on an extension of the vibrating member. Active noise canceller.