JP3344147B2 - Speaker system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a speaker system provided with a microphone for noise cancellation and characteristic correction.

[0002]

2. Description of the Related Art A speaker system has been developed in which a small microphone is arranged at a sound pressure output portion of a speaker, and noise cancellation and output characteristic correction are performed using a sound signal collected by such a microphone.

FIGS. 10 (a), 10 (b) and 10 (c) show, for example, a microphone 44 for noise cancellation arranged in a speaker sound pressure output portion 42 of a cordless telephone 41. FIG. 10A is a perspective view, FIG. 10B is a front view of the speaker sound pressure output part 42, and FIG. 10C shows the internal structure of the speaker sound pressure output part 42. FIG.
As can be seen from (c), a small microphone 44 is arranged at the speaker sound pressure output part 42 which is in the front direction of the speaker unit 43.

In the microphone 44, external noise is mixed together with the output sound from the speaker unit 43 to obtain an audio signal. Then, a predetermined compensation process is performed on the audio signal from the microphone 44 and the result is feedback-added to the input signal to the speaker unit 43, so that a so-called noise canceling operation can be performed. A speaker system that is easy to hear even underneath can be realized.

FIG. 11 shows an acoustic feedback type (AFB: Acoustic F) capable of correcting the frequency characteristics of the output sound pressure.
5 shows a speaker box 50 employing an eedBack system). On the front side of the diaphragm of the speaker unit 51 in the speaker box 50, a small microphone 52 is arranged as shown in the figure. The microphone 52 collects the output sound from the speaker unit 51, and the audio signal from the microphone 52 is subjected to a predetermined compensation process and then compared with the input audio signal to the speaker unit 51. become.

The result of this comparison is a signal indicating whether the speaker unit is driven faithfully with respect to the input signal. Based on this comparison result, the speaker unit 5
By correcting the input signal to 1, it is possible to improve the disturbance of the sound pressure frequency characteristic due to the acoustic load, and to improve the responsiveness and the sound quality.

[0007]

The microphone 4 is used for such noise cancellation and characteristic correction.
When the microphones 4 and 52 are arranged, it is necessary that the microphones 44 and 52 can easily pick up the sound from the speaker units 43 and 51. Therefore, as shown in FIG. Have been placed.
The microphone axis JM, which is the vibration direction of the diaphragm of the microphones 44 and 52, is
A speaker axis JS which is the vibration direction of the diaphragms of 3 and 51,
It is set to be in a parallel state.

However, in such a speaker system, there is a problem that the microphones 44 and 52 easily pick up vibration noise of the microphones. That is, when the diaphragms of the speaker units 43 and 51 vibrate in the direction of the speaker axis JS, the vibration also causes the housing surface to vibrate in the same direction. Then, the microphones 44 and 52 themselves are also vibrated in that direction, whereby the diaphragms of the microphones 44 and 52 are vibrated, that is, vibration noise is picked up. When such vibration noise is added to the output of the microphone 44, a good noise canceling operation cannot be performed.
Further, if such vibration noise is added to the output of the microphone 52, the frequency characteristics and responsiveness of the output sound pressure of the speaker unit 52 cannot be improved.

[0009]

SUMMARY OF THE INVENTION In view of the above-mentioned problems, the present invention arranges a microphone at a sound pressure output portion from a speaker and performs predetermined signal processing using an audio signal obtained from the microphone. It is an object of the speaker system configured as described above to make it difficult for the microphone to pick up vibration noise.

[0010] For this purpose, the microphone is used for the speaker.
Attached to a housing having
In addition, the microphone is positioned relative to the speaker so that the speaker axis, which is the vibration direction of the speaker diaphragm, and the microphone axis, which is the vibration direction of the microphone diaphragm, are substantially perpendicular to each other. Set.

With such a configuration, a predetermined compensation process is performed on the audio signal obtained by the microphone, and the resulting signal is fed back to the input signal to the loudspeaker to reduce the noise at the sound pressure output portion from the loudspeaker. I do.

Alternatively, the audio signal obtained by the microphone is subjected to predetermined compensation processing for the audio signal , and is fed back to the input signal to the speaker to correct the output characteristics of the speaker.

[0013]

The microphone diaphragm is positioned so that the speaker axis, which is the vibration direction of the speaker diaphragm, and the microphone axis, which is the vibration direction of the microphone diaphragm, are substantially perpendicular to each other. And the effect of vibration noise generated in the housing is suppressed.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction of the first and second embodiments of the present invention will be described below, and then the principle common to each embodiment will be described.

FIG. 1 shows a speaker system employed in a telephone device, in which a microphone 4 for noise cancellation is arranged in a speaker sound pressure output portion 2 of a cordless telephone 1. 1A is a perspective view, FIG. 1B is a front view of the speaker sound pressure output unit 2, and FIG. 1C shows the internal structure of the speaker sound pressure output unit 2.

As can be seen from FIG. 1 (c), a small microphone 4 is arranged in a speaker sound pressure output portion 2 which is in front of the speaker unit 3. Here, in the case of the present embodiment, the microphone 4 is arranged such that the microphone axis JM, which is the vibration direction of the diaphragm, is substantially perpendicular to the speaker axis JS, which is the vibration direction of the diaphragm of the speaker unit 3. Have been.

In the microphone 4, external noise is mixed with the output sound from the speaker unit 3 to obtain an audio signal. By performing a predetermined compensation process on the audio signal from the microphone 4 and adding it back to the input signal to the speaker unit 3, a so-called noise canceling operation can be performed. A speaker system that is easy to hear even underneath can be realized.

FIG. 2 shows a principle block for noise cancellation. The audio signal is supplied from terminal 11 to adder 12
Is supplied to the power amplifier 13 via the amplifier and amplified as a speaker drive signal. Then, the speaker drive signal is supplied to the speaker 14 and output as a sound pressure. Here, the speaker 14 corresponds to the speaker unit 3 in FIG.

The output sound pressure of the speaker 14 is shown in FIG.
As shown equivalently as 5, the sound pressure P mixed with the external noise N reaches the user's ear (eardrum). Here, the sound pressure P is picked up as shown by the microphone / amplifier 16 and output as an audio signal. The microphone / amplifier 16 is the microphone 4 of FIG.
And an amplifier circuit. The output of the microphone / amplifier 16 is subjected to predetermined signal processing in a feedback circuit 17, and outputs an added signal for noise reduction. This is supplied to the adder 12, and the adder 12 performs a process of subtracting a noise component from the audio signal from the terminal 11.

Here, a power amplifier 13, a speaker 14,
The transfer functions of the microphone / amplifier 16 and the feedback circuit 17 are A, H, M, and -β. When the sound at the ear picked up by the microphone / amplifier 16 is fed back through the fixed filter in the feedback circuit 17 as shown in FIG.
Noise is expressed as sound pressure P and noise N.

(Equation 1) It has an effect that can be reduced.

Since such a circuit can be constituted by an analog circuit, it has excellent followability and small scale.
Also, as a condition that this system does not oscillate, since each transfer function is a complex number,

(Equation 2) It is necessary to be.

In the loudspeaker system of this embodiment having such a noise canceling circuit configuration, as described above, the microphone 4 is arranged so that its microphone axis JM is substantially perpendicular to the speaker axis JS. As a result, the vibration noise of the microphone 4 due to the influence of the vibration of the diaphragm of the speaker unit 3 can be suppressed, whereby the accuracy of the sound pressure-voltage conversion of the microphone 4 is improved, and more effective noise suppression is achieved. Will be realized.

It is needless to say that the speaker system as shown in FIGS. 1 and 2 can be favorably applied not only to a telephone but also to a speaker portion of another communication device, a headphone, a hearing aid, and the like.

FIG. 3 shows an AFB as a second embodiment.
1 shows a speaker box 20 employing an (Acoustic FeedBack system). A small microphone 22 is arranged on the front side of the diaphragm of the speaker unit 21 in the speaker box 20 as shown in the figure. In particular, in the case of the present embodiment, the microphone 22 is arranged such that the microphone axis JM, which is the vibration direction of the diaphragm, is substantially perpendicular to the speaker axis JS, which is the vibration direction of the diaphragm of the speaker unit 21. ing.

The microphone 22 collects the output sound from the speaker unit 21, and the audio signal from the microphone 22 is subjected to AFB by a circuit as shown in FIG.
Used for processing. In FIG. 4, an audio signal is supplied to a terminal 31.
Is supplied to the power amplifier 33 via the comparator 32 and is amplified as a speaker drive signal. Then, the speaker drive signal is supplied to the speaker 34 and output as a sound pressure. Here, the speaker 34 corresponds to the speaker unit 21 in FIG.

The output sound pressure of the speaker 34 is picked up by the microphone 22 of FIG. 3 and a microphone / amplifier 35 corresponding to an amplifier circuit and output as an audio signal. The output of the microphone / amplifier 35 is a compensation circuit 3
In 6, predetermined signal processing is performed, and the result is supplied to the comparator 32.

In such a configuration, the microphone /
After a predetermined compensation process is performed on the output of the amplifier 35,
1 will be compared with the input audio signal. The comparison result is a signal indicating whether the speaker unit is driven faithfully with respect to the input signal. By correcting the drive signal to the speaker 34 by the power amplifier 33 based on the comparison result, it is possible to improve the disturbance of the sound pressure frequency characteristics due to the acoustic load and to improve the responsiveness and the sound quality. It can also be used to improve low-frequency deficiency in small-diameter speaker systems.

In a speaker system employing such an AFB, as described above, the microphone 22
Since the microphone axis JM is disposed so as to be substantially perpendicular to the speaker axis JS, vibration noise of the microphone 22 due to the influence of vibration of the diaphragm of the speaker unit 21 can be suppressed. As a result, the S / N of the sensitivity of the microphone 22 is improved, and the AFB
Therefore, the control of the improvement of the response, the flattening of the frequency characteristic, the enhancement of the low frequency band, and the like, which are the original objectives of the present invention, can be executed more reliably and effectively, and a high-quality sound reproduction speaker system can be realized.

The fact that the vibration noise of the microphones 4 and 22 can be reduced by the configuration of the first and second embodiments will be described in detail. Normally, when the microphone unit main body is vibrated, even if the back pole makes the same movement as the unit main body, the diaphragm cannot keep up with the movement and generates vibration noise.

Considering the case where the microphone unit is a condenser microphone, the mechanical system of the unit is shown by an electrical equivalent circuit as shown in FIG. Here, the mechanical force F corresponds to a voltage, and the speed v corresponds to a current. And
pS is the input sound pressure × area, and pSε- ^jkdcosΦ is the input sound pressure coming from the back, that is, the multiplier of ε indicates a time delay component.

Considering the sensitivity of the condenser microphone having such an equivalent circuit in the front direction in the plane wave sound field. First, the vibration speed v of the diaphragm is

(Equation 3) Can be represented by Here, k = ω / C, C is the speed of sound, d is the distance between two acoustic terminals, α = (Cr ₁ c ₁ ) / d, Z ₀
= Jωm ₀ + r ₀ + (1 / jωc ₁ ).

Next, a case where the microphone unit body vibrates will be obtained. An equivalent circuit when the unit body vibrates is as shown in FIG. J relative speed of the microphone unit body and the diaphragm is in V-V _0, the excitation force contributing to power generation is an inertial force based on the equivalent mass of the diaphragm
ωm ₀ V ₀ . Here, regarding the relative speed V−V ₀ ,

(Equation 4) It can be.

The relative velocity of the diaphragm normalized by the front sensitivity (vibration velocity) is given by the above (Equation 3) and (Equation 4).

(Equation 5) Becomes And for an omnidirectional microphone, α = ∞,

(Equation 6) Becomes

This indicates that the vibration noise is proportional to the surface density m ₀ / S and the vibration acceleration ωV. And α =
Compared to the non-directional microphone as ∞, the sound pressure gradient type microphone generates vibration noise as shown in FIG. 7 from (Equation 5) and (Equation 6).

After all, if the diaphragm is a mere flat plate, the vibration sensitivity changes depending on the vibration direction, and the above-described vibration noise is generated when the diaphragm is vibrated in a direction perpendicular to the diaphragm. It is understood that even if the vibration is applied in the parallel direction, the back pole and the diaphragm move together, so that no vibration noise is generated. That is, in the case of the first and second embodiments, the diaphragms of the microphones 4 and 22 are
Since vibration is applied in a direction parallel to the diaphragm, vibration noise hardly occurs.

The characteristics of the microphone 4 of the first embodiment in FIG. 1 and the microphone 44 of FIG.
8 and 9 show the measurement results of the characteristics of FIG. FIG. 8 shows the frequency-gain characteristics of the microphone, and FIG. 9 shows the frequency-phase characteristics of the microphone. At the same time, a measurement result of a sound field measurement microphone which is arranged separately from a housing having a speaker and is originally not affected by vibration noise is also shown. The solid line in the figure indicates the characteristics of the microphone 4 in the embodiment in which the microphone axis JM is perpendicular to the speaker axis JS, the dashed line indicates the characteristics of the conventional microphone 44 in which the microphone axis JM is in parallel with the speaker axis JS, and the broken line indicates This is the characteristic of the sound field measurement microphone.

As can be seen from the figures, the microphone 44 arranged in the conventional manner has a characteristic in which the low-frequency range is considerably raised with respect to the original sound collection characteristic which is the result of the microphone for sound field measurement, and the sound field is accurate. It is shown that the microphone 4 cannot be picked up, but by arranging the microphone 4 as in the present embodiment, substantially the same characteristics as those of the microphone for sound field measurement can be obtained. In other words, it can be seen that the sound field has been accurately picked up.

Considering the noise canceling feedback circuit configuration, in the case of the microphone 44 in the conventional arrangement, the phase rotation becomes large due to the unnecessary rise of the low frequency component, and the compensation processing in the feedback circuit becomes complicated. . At the same time, since the limited range of the phase condition for preventing the system from oscillating is limited, the noise reduction band is narrowed, and the noise reduction effect is reduced. On the other hand, in the case of the microphone 4 in the arrangement state of the present embodiment, low-frequency characteristics are suppressed, the degree of freedom of the feedback circuit is increased, and a more effective noise reduction effect can be obtained. The same applies to the speaker system employing the AFB. That is, according to the configuration of the second embodiment, the AFB
The characteristic correction function and the like are greatly improved.

[0039]

As described above, according to the speaker system of the present invention, the position of the speaker axis, which is the vibration direction of the diaphragm of the speaker, and the position of the microphone axis, which is the vibration direction of the diaphragm of the microphone, are substantially perpendicular to each other. So that
By setting the arrangement state of the microphone with respect to the speaker, there is an effect that it is possible to effectively prevent the microphone from picking up vibration noise. .

With such a configuration, predetermined compensation processing is performed on the audio signal obtained by the microphone, and the resulting signal is fed back to the input signal to the speaker, so that noise at the sound pressure output portion from the speaker is reduced. In this case, the microphone performs high-precision sound pressure-to-voltage conversion that does not include vibration noise, thereby realizing more effective noise suppression.

[0041] The pair to the audio signal obtained by the microphone
Also, when a predetermined compensation process is performed to feed back to the input signal to the loudspeaker to correct the output characteristics of the loudspeaker, the microphone can perform high-precision sound pressure-voltage conversion without vibration noise. Is performed more effectively and accurately in terms of flattening of frequency characteristics, improvement of responsiveness, low-frequency compensation, and the like, and a high-quality speaker system can be realized.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a noise canceller configuration in the first embodiment.

FIG. 3 is an explanatory diagram of a second embodiment of the present invention.

FIG. 4 is an explanatory diagram of an AFB configuration according to a second embodiment.

FIG. 5 is an equivalent circuit diagram of the condenser microphone.

FIG. 6 is an equivalent circuit diagram when the main body of the condenser microphone vibrates.

FIG. 7 is an explanatory diagram of vibration sensitivity of a sound pressure gradient type microphone.

FIG. 8 is an explanatory diagram of frequency-gain characteristics in a state where microphones of the present invention and the conventional example are arranged.

FIG. 9 is an explanatory diagram of frequency-phase characteristics in a state where microphones of the present invention and a conventional example are arranged.

FIG. 10 is an explanatory diagram of a conventional speaker system.

FIG. 11 is an explanatory diagram of a conventional speaker system.

[Explanation of symbols]

 3,21 Speaker unit 4,22 Microphone 12 Adder 13,33 Power amplifier 14,34 Speaker 16,35 Microphone / amplifier 17 Feedback circuit 32 Comparator 36 Compensation circuit

Continuation of the front page (56) References JP-A-5-316588 (JP, A) JP-A-61-108294 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04R 3 / 00 310 H04R 3/04 101

Claims (2)

(57) [Claims] An audio signal obtained by a microphone disposed at a sound pressure output portion from a speaker is subjected to a predetermined compensation processing so that an input signal to the speaker is fed back.
And a microphone system configured to reduce external noise in the sound pressure output portion , wherein the microphone is attached to a housing having the speaker or a support portion provided in the housing. A speaker axis that is a vibration direction of the diaphragm of the speaker;
An arrangement state of the microphone is set with respect to the speaker so that a microphone axis that is a vibration direction of the diaphragm of the microphone is substantially perpendicular to each other , and the microphone vibrates based on the vibration of the speaker. Miscellaneous
A speaker system that performs sound pressure-voltage conversion that does not include sound . 2. A sound pressure output portion from a speaker.
A predetermined compensation processing is performed on the audio signal obtained by the microphone.
Feedback to the input signal to the speaker.
To correct the output characteristics of the speaker.
In the formed speaker system, the microphone is a housing having the speaker or
A speaker shaft attached to a supporting portion provided in the housing and being in a vibration direction of a diaphragm of the speaker;
Microphone in the vibration direction of the diaphragm of the microphone
So that the shafts are in a substantially vertical position with respect to each other.
The microphone placement status is set for the speaker
And the microphone receives vibration noise based on the vibration of the speaker.
A sound pressure-voltage conversion that does not include sound.
Peeker system.