JP2005091633A - Transmitted sound reducing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transmitted sound reducing device that is capable of easily handling noises arriving from both directions on a small scale. <P>SOLUTION: The transmitted sound reducing device reduces a noise arriving from a specified direction and transmitted through the device itself and propagated. The transmitted sound reducing device is equipped with a 1st electroacoustic transducer, a 2nd electroacoustic transducer, and a 1st control part. The 1st electroacoustic transducer detects a noise, converts the detected noise into an electric signal, and outputs it. The 2nd electroacoustic transducer has its vibration surface arranged opposed to a vibration surface of the 1st electroacoustic transducer and radiates a sound to the vibration surface of the 1st electroacoustic transducer. The 1st control part controls driving of the 2nd electroacoustic transducer according to the electric signal to attenuate the level of the electric signal outputted from the 1st electroacoustic transducer. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a transmitted sound reducing device, and more particularly to a transmitted sound reducing device that actively reduces sound transmitted through a wall surface.

  Along with the high output of transportation facilities and the densely populated houses, there is a need to reduce noise in the living environment. In recent years, home theaters have been widely used in homes, but as a result of considering leakage of noise to the neighborhood, it was not possible to appreciate content at a sufficient volume. Conventionally, in addition to the passive method of increasing the weight of the wall surface as a means for preventing noise or filling the wall surface with a sound absorbing material, various transmitted sound reduction devices that actively suppress wall surface vibration due to noise and reduce noise. It has been proposed (see, for example, Patent Document 1). Hereinafter, a conventional transmitted sound reducing device that actively reduces wall noise will be described with reference to the drawings.

  FIG. 16 is a diagram illustrating a conventional transmitted sound reducing device. In FIG. 16, a sound insulation panel 161 which is a transmitted sound reducing device has a configuration in which a large number of cells 162 are arranged. FIG. 17 is a diagram showing a detailed configuration of the cell 162 shown in FIG. In FIG. 17, the cell 162 includes an actuator 173, a first sensor 174, a second sensor 175, and partition walls 177 and 178. In addition, as shown in FIG. 17, the sound insulation panel 161 is provided with the control apparatus 176 for every cell. The first and second sensors 174 and 175 are, for example, PVDF sensors (or other sensors). The control device 176 generates a control signal based on signals from the first and second sensors 174 and 175. The actuator 173 receives a control signal generated by the control device 176.

  First, a mechanism for transmitting noise through the sound insulation panel 161 will be described. Here, a case is considered where the sound insulation panel 161 is placed in an environment where noise comes from the partition wall 177 to the partition wall 178. In this case, as the partition wall 177 is excited by noise, the partition wall 177 becomes a sound source and radiates sound toward the partition wall 178. As a result of the partition 178 being excited by the sound radiated from the partition 177, the partition 178 becomes a sound source and emits sound. By such a mechanism, noise is transmitted from the partition 177 toward the partition 178.

Next, an operation in which the sound insulation panel 161 actively reduces noise will be described. First, the vibration state of the partition wall 177 is detected by the first sensor 174, and the detection result is input to the control device 176 as a reference signal. The control device 176 inputs a control signal generated based on the reference signal from the first sensor to the actuator 21. The second sensor 175 detects an interference state between the excitation action of the actuator 21 on the partition wall 178 and the excitation action of noise on the partition wall 178 and inputs the detected state to the control device 176. The control device 176 updates the filter coefficient for generating the control signal based on an adaptive algorithm such as Filtered-X LMS so that the signal level of the second sensor 175 approaches zero. Here, the noise signal detected by the first sensor 174 is N, the transfer characteristic from the first sensor 174 to the second sensor 175 is H, the transfer characteristic from the actuator 21 to the second sensor 175 is C, and the control is performed. If the signal generation filter characteristic is G,
N · H + N · G · C = 0 (1)
When the condition is satisfied, the signal level of the second sensor 175 becomes zero. Therefore, the control device 176
G = −H / C (2)
The filter coefficient is updated so as to realize the filter characteristic. As the control device 176, a fixed analog filter can be used.

By setting the filter coefficient in the control device 176 as described above, the signal level of the second sensor 175 can be brought close to 0, that is, the vibration level of the partition 178 can be brought close to 0. As a result, the level of sound radiated from the partition 178 is reduced. When all of the cells constituting the sound insulation panel 161 perform the above-described operation, noise transmitted through the sound insulation panel 161 can be reduced.
Japanese National Patent Publication No. 8-500193

  However, in the configuration shown in FIGS. 16 and 17, noise cannot be reduced in an environment where noise comes in the direction from the partition 178 to the partition 177. This is because if the noise transmitted in the direction from the partition wall 178 to the partition wall 177 is reduced by the above configuration, the actuator 173 installed in the partition wall 178 where the noise propagates first passes through the actuator 173 where the noise propagates later. This is because the control must be performed based on the signal from the first sensor installed at 177. It is impossible to reduce noise by control that does not satisfy such causality. That is, the sound insulation panels shown in FIGS. 16 and 17 can only deal with noise from one direction and cannot deal with noise from both directions. Therefore, if the sound insulation panel 161 is made to correspond to noise from the opposite direction, the sound insulation panel 161 must be removed from the wall surface and installed in the opposite direction. Is impossible.

  In order to cope with noise from both directions, an arrangement may be considered in which an actuator is also attached to the partition wall 177 and a signal from the second sensor 175 is used as a reference signal. However, this configuration requires two sensors and two actuators, which must be attached to the partition wall, increasing the scale of the apparatus.

  SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a transmitted sound reduction device that is small and can easily cope with noise coming from both directions.

  In order to achieve the above object, the noise reduction device of the present invention has the following features. That is, the first invention is a transmitted sound reducing device that reduces noise that arrives from a predetermined direction and propagates through the own device. The transmitted sound reducing device includes a first electroacoustic transducer, a second electroacoustic transducer, and a first control unit. The first electroacoustic transducer detects noise, converts the detected noise into an electrical signal, and outputs the electrical signal. The vibration surface of the second electroacoustic transducer is disposed to face the vibration surface of the first electroacoustic transducer, and radiates sound to the vibration surface of the first electroacoustic transducer. The first control unit controls the driving of the second electroacoustic transducer based on the electrical signal so that the level of the electrical signal output from the first electroacoustic transducer is attenuated.

  In the second invention, when noise comes from a direction opposite to the predetermined direction, the second electroacoustic transducer detects the noise, converts the detected sound into an electric signal, and outputs it. May be. At this time, the first control unit controls the driving of the first electroacoustic transducer based on the electrical signal so that the electrical signal output from the second electroacoustic transducer is attenuated. . The first electroacoustic transducer emits sound to the vibration surface of the second electroacoustic transducer according to the control by the first control unit.

  Further, in the third invention, the transmitted sound reducing device inputs the detection result of the noise by the first and second electroacoustic transducers, and the noise arrives from the predetermined direction based on the detection result. Or a determination unit that determines whether the arrival is from the opposite direction. At this time, when the determination unit determines that noise comes from the predetermined direction, the first control unit performs the second electroacoustic conversion based on a detection result of the first electroacoustic transducer. The first electroacoustic transducer is driven based on the detection result of the second electroacoustic transducer when it is determined by the determination unit that the noise comes from the opposite direction. Control.

  In the fourth invention, the determination unit may perform determination at predetermined time intervals.

  In the fifth invention, the transmitted sound reducing device is connected to the vibration surface of the first electroacoustic transducer, and forms a sealed space with a variable volume between the vibration surface and the first electroacoustic transducer. You may further provide the housing | casing and the 2nd housing | casing which forms the sealed space which is connected to the vibration surface of the said 2nd electroacoustic transducer, and whose volume is variable between the said vibration surfaces.

  In the sixth aspect, the first electroacoustic transducer preferably has the same electroacoustic transduction characteristics as the second electroacoustic transducer.

  In the seventh invention, the first control unit is typically constituted by a signal inverting amplifier.

  In the eighth invention, the first and second electroacoustic transducers are typically flat-plate piezoelectric acoustic bodies.

  In the ninth invention, the transmitted sound reducing device may include a third electroacoustic transducer, a fourth electroacoustic transducer, a second control unit, and a connection unit. The third electroacoustic transducer detects noise, converts the detected noise into an electrical signal, and outputs the electrical signal. The vibration surface of the fourth electroacoustic transducer is disposed to face the vibration surface of the third electroacoustic transducer, and radiates sound to the vibration surface of the third electroacoustic transducer. The second control unit controls driving of the fourth electroacoustic transducer based on the electrical signal so that the electrical signal output from the third electroacoustic transducer is attenuated. The connection portion forms a sealed space between the first electroacoustic transducer and the fourth electroacoustic transducer.

  In the tenth aspect of the invention, the first resonance frequency of the first and second electroacoustic transducers is set to the same value, and the first resonance frequency of the third and fourth electroacoustic transducers is The same value may be set. At this time, the primary resonance frequency of the first and second electroacoustic transducers is set to a value different from the primary resonance frequency of the third and fourth electroacoustic transducers.

  The eleventh invention is a noise control panel configured by the transmitted sound reducing device according to the first invention. The noise control panel includes a plurality of transmitted sound reducing devices and a support portion that supports the outer peripheries of the first and second electroacoustic transducers of each transmitted sound reducing device. In addition, each transmitted sound reduction device is connected side by side in a direction substantially parallel to the vibration surfaces of the first and second electroacoustic transducers by the support portion.

  As described above, according to the present invention, two electroacoustic transducers having a function of detecting noise and a function of emitting control sound for reducing noise are used. One electroacoustic transducer is used for detecting noise, and the other is used for emitting control sound. Here, since each electroacoustic transducer has both functions, it can be used for any application. Therefore, when it is installed to reduce noise coming from a predetermined direction, it is not necessary to change the arrangement of each electroacoustic transducer in order to cope with noise coming from the opposite direction. As described above, according to the transmitted sound reducing device according to the present invention, it is possible to easily cope with noise coming from the opposite direction.

  Moreover, according to the 2nd invention, it can respond to the noise from two directions. Furthermore, according to the third invention, it is possible to automatically cope with noise from both directions. Furthermore, according to the fourth aspect of the invention, it is possible to reliably reduce noise even when the direction in which noise arrives changes from moment to moment.

  According to the fifth aspect, the primary resonance frequency of the electroacoustic transducer can be changed by changing the volume. Therefore, the frequency band of noise that can be reduced by the transmitted sound reducing device can be changed.

  Further, according to the sixth aspect, the design of the control unit can be facilitated. According to the seventh invention, the control unit can be realized with a simple configuration.

  According to the ninth aspect, the effect of reducing the sound is performed twice with respect to the noise. Therefore, the noise reduction effect can be further improved. Furthermore, according to the tenth aspect, it is possible to obtain a noise reduction effect in a wider frequency band than in the case where the action of reducing the sound with respect to the noise is performed only once.

  Further, according to the eleventh aspect, the transmitted sound reducing device can be installed in a wider range.

(Embodiment 1)
First, the transmitted sound reducing apparatus according to Embodiment 1 of the present invention will be described. FIG. 1 is a diagram illustrating a transmitted sound reduction device according to the first embodiment. In FIG. 1, the transmitted sound reducing device includes piezoelectric acoustic bodies 11 and 12 that are examples of an electroacoustic transducer, and a control unit 13. The piezoelectric acoustic bodies 11 and 12 are flat-plate electroacoustic transducers using the piezoelectric effect. The control unit 13 is connected to the piezoelectric acoustic bodies 11 and 12. The transmitted sound reducing apparatus shown in FIG. 1 can reduce the system scale as compared with the conventional configuration shown in FIG. 17, and can easily cope with noise from both directions. Hereinafter, the operation of the transmitted sound reducing device will be described.

  In FIG. 1, consider an environment in which noise arrives from the left side (in the paper) of the transmitted sound reduction device and passes in the right direction. Under this environment, the noise transmitted through the piezoelectric acoustic body 12 excites the piezoelectric acoustic body 11, and as a result, an electromotive force is generated in the piezoelectric acoustic body 11 due to the piezoelectric effect. The signal generated by this electromotive force indicates noise transmitted to the right side (side where noise should be reduced) of the transmitted sound reducing device shown in FIG. Therefore, the control unit 13 inputs a signal output from the piezoelectric acoustic body 11 as a noise signal, and controls the piezoelectric acoustic body 12 based on the noise signal. That is, the piezoelectric acoustic body 11 is used as a microphone for noise detection.

  As the piezoelectric acoustic body 11, for example, a piezoelectric speaker as disclosed in JP-A-11-164396 can be used. In the first embodiment, a piezoelectric speaker having a thickness of 200 [μm] was used as the piezoelectric acoustic body 11 and its characteristics were measured. FIG. 2 is a diagram illustrating the characteristics of the piezoelectric speaker used in the first embodiment as a microphone. In FIG. 2, the vertical axis represents sensitivity, and the horizontal axis represents frequency. The frequency band of 150 to 200 [Hz] at which the sensitivity reaches a peak matches the primary resonance frequency of the piezoelectric speaker. At this time, the vibration surface of the speaker resonates in the (1, 1) mode. In addition, the piezoelectric speaker has a feature that the microphone sensitivity decreases at a frequency higher than the primary resonance frequency.

  On the other hand, in FIG. 1, the control unit 13 generates a control signal for controlling the operation of the piezoelectric acoustic body 12 based on the noise signal output from the piezoelectric acoustic body 11 and outputs the control signal to the piezoelectric acoustic body 12. The piezoelectric acoustic body 12 operates according to a control signal and emits sound. The sound radiated by the piezoelectric acoustic body 12 serves as a control sound for suppressing the vibration of the piezoelectric acoustic body 11. That is, the piezoelectric acoustic body 12 operates as a control speaker that emits control sound.

  As the piezoelectric acoustic body 12, a piezoelectric speaker similar to the piezoelectric acoustic body 11 can be used. In the first embodiment, the same piezoelectric speaker as the piezoelectric acoustic body 11 is used as the piezoelectric acoustic body 12. FIG. 3 is a diagram illustrating a characteristic of sound pressure generated by the piezoelectric speaker (generated sound pressure characteristic). In FIG. 3, the vertical axis indicates the sound pressure level, and the horizontal axis indicates the frequency. The generated sound pressure characteristic of the piezoelectric speaker shows a remarkable peak at 150 to 200 [Hz], similarly to the microphone characteristic.

  Next, a control method in the control unit 13 will be described. The control unit 13 controls the driving of the piezoelectric acoustic body 12 based on the noise signal so that the level of the noise signal output from the piezoelectric acoustic body 11 is attenuated (preferably as small as possible). Specifically, the control unit 13 controls the piezoelectric acoustic body 12 such that vibration having a phase opposite to that of the piezoelectric acoustic body 11 due to noise is applied to the piezoelectric acoustic body 11 by the control sound. Hereinafter, the control method in the control unit 13 will be described in detail.

で表される。さらに、（４）式より、

を実現するようにフィルタ特性Ｃを設計すれば、圧電音響体１１の振動を抑制し、騒音を低減することができる。すなわち、騒音を低減するためには、オープンループ特性Ｐ・Ｃを、位相が逆相、つまり±１８０［ｄｅｇ］となるようにすればよい。これによって、圧電音響体１１からの騒音信号が減衰するように制御することができる。そして、Ｐ・Ｃが逆相となる周波数において、そのゲインが大きいほど、騒音信号の減衰量も大きくなる。以上のように、制御部１３のフィルタ特性は、（５）式を満たすように設定される。 Now, N is a signal generated in the piezoelectric acoustic body 11 due to noise, C is a filter characteristic of the control unit 13, P is a signal transmission characteristic of the sound radiated by the piezoelectric acoustic body 12 to the piezoelectric acoustic body 11, and noise and control sound. If the vibration of the piezoelectric acoustic body 11 after the interference, that is, the control error is e,
e = N + e · P · C (3)
This relationship holds. From the equation (3), the ratio of the control error e to the noise N is

It is represented by Furthermore, from equation (4)

If the filter characteristics C are designed so as to realize the above, vibration of the piezoelectric acoustic body 11 can be suppressed and noise can be reduced. That is, in order to reduce noise, the open loop characteristic P · C may be set so that the phase is opposite, that is, ± 180 [deg]. Thereby, it is possible to control so that the noise signal from the piezoelectric acoustic body 11 is attenuated. Then, at the frequency where P · C is in the opposite phase, the greater the gain, the greater the attenuation of the noise signal. As described above, the filter characteristics of the control unit 13 are set so as to satisfy the expression (5).

  FIG. 4 is a diagram showing a transmitted sound reducing apparatus when the control unit 13 shown in FIG. 1 is realized by a signal inverting amplifier. As shown in FIG. 4, the control unit 13 can be realized by a signal inverting amplifier 41. In FIG. 4, the piezoelectric acoustic bodies 11 and 12 are realized by the above-described piezoelectric speaker. FIG. 5 is a diagram illustrating the P / C characteristics of the transmitted sound reducing device shown in FIG. As shown in FIG. 5, the gain has a significant peak in the frequency band of 150 to 200 [Hz] and the frequency band of 500 to 600 [Hz], which are the primary resonance frequencies of the piezoelectric speaker. In these frequency bands, the phase is close to ± 180 [deg]. Therefore, the transmitted sound reduction apparatus shown in FIG. 4 has noise reduction performance in these frequency bands. That is, the transmitted sound reducing device shown in FIG. 4 can reduce noises at these frequencies.

  6 is a diagram showing an evaluation device for evaluating the performance of the transmitted sound reducing device shown in FIG. In FIG. 6, the evaluation device includes a transmitted sound reduction device 61, a noise generator 62, a noise source speaker 63, a rigid box 64, a microphone 65, a frequency analyzer 66, and a housing 67. Yes. The transmitted sound reducing device 61 is the transmitted sound reducing device shown in FIG. 4 and includes piezoelectric acoustic bodies 11 and 12 and a signal inverting amplifier 41. The piezoelectric acoustic bodies 11 and 12 are fixed in a rigid box 64. In the evaluation apparatus shown in FIG. 6, the noise generator 62 generates, for example, a white noise signal as a noise signal and outputs the white noise signal to the noise source speaker 63. The noise source speaker 63 radiates the noise signal output from the noise generator 62 to the space surrounded by the rigid box 64. The periphery of the noise source speaker 63 is surrounded by a housing 67. The housing 67 is for preventing the sound emitted from the back surface of the noise source speaker 63 from being detected by the microphone 65. The noise radiated to the space passes through the piezoelectric acoustic bodies 11 and 12 and propagates outside the rigid box 64. The rigid box 64 plays a role of preventing noise from being transmitted from other than the piezoelectric acoustic bodies 11 and 12. The microphone 65 detects noise propagating to the outside of the rigid box 64. The detected noise is input to the frequency analyzer 66. The frequency analyzer 66 derives the frequency characteristics of the input noise. By looking at the frequency characteristics derived by the frequency analyzer 66, the noise reduction effect by the transmitted sound reduction device 61 can be seen.

  FIG. 7 is a diagram showing the frequency characteristics of noise detected by the microphone 65 when the transmitted sound reducing device 61 is not driven and when the transmitted sound reducing device 61 is driven using the evaluation device shown in FIG. The frequency characteristics shown in FIG. 7 are such that the rigid box 64 is formed of an acrylic plate having a thickness of 30 [mm], and the microphone 65 is positioned 30 cm away from the piezoelectric acoustic body 11 in front of the piezoelectric acoustic body 11. This is the characteristic obtained when installed on the front (above the paper).

  In FIG. 7, the solid line indicates the frequency characteristic when the transmitted sound reducing device 61 is not driven, and the broken line indicates the frequency characteristic when the transmitted sound reducing device 61 is driven. As shown in FIG. 7, in the frequency band of 150 to 200 [Hz] which is the primary resonance frequency of the piezoelectric speaker, the noise is more increased when the transmitted sound reduction device 61 is driven than when it is not driven. It turns out that it can reduce. In particular, when the frequency is about 170 [Hz], the noise can be reduced by about −13 [dB] when the transmitted sound reducing device 61 is driven, compared to when the transmitted sound reducing device 61 is not driven. From the above, it can be seen that a sufficient noise reduction effect can be obtained even if the control unit 13 is realized by a simple configuration such as a signal inverting amplifier.

  As described above, the transmitted sound reducing apparatus according to Embodiment 1 can reduce noise with respect to noise having a predetermined frequency component. The band of the frequency component that can be reduced is a frequency band near the primary resonance frequency of the piezoelectric speaker used as the piezoelectric acoustic body. Therefore, if the frequency spectrum of the noise to be reduced is analyzed in advance and the piezoelectric speaker is designed based on the analysis result, the noise in the desired frequency band can be reduced. Further, in the passive method such as increasing the weight of the wall surface, it is difficult to reduce the noise in the low frequency band of about 150 to 200 [Hz] described above, but the transmitted sound reduction according to the first embodiment is performed. According to the apparatus, it is possible to reduce noise in such a low frequency band.

  Furthermore, the transmitted sound reducing apparatus according to Embodiment 1 can easily cope with noise from both directions. FIG. 8 is a diagram showing a transmitted sound reducing device in an environment where noise comes from the opposite direction to that in FIG. The configuration shown in FIG. 8 is different from the configuration shown in FIG. 1 in that the piezoelectric acoustic body 12 is operated as a noise detection microphone and the piezoelectric acoustic body 11 is operated as a control speaker. The other points of the transmitted sound reducing apparatus shown in FIG. 8 are the same as those in FIG. 1, and the operation is also the same as that of the transmitted sound reducing apparatus shown in FIG.

  Here, since the piezoelectric acoustic bodies 11 and 12 can be realized by the same configuration, in order to change the configuration shown in FIG. 1 to the configuration shown in FIG. 8, only the configuration of the control unit 13 needs to be changed. Therefore, only the configuration of the control unit 13 needs to be changed in order to make the transmitted sound reduction apparatus shown in FIG. 1 correspond to noise coming from the opposite direction. Specifically, the configuration may be changed so that the piezoelectric acoustic body 12 is controlled based on a signal input from the piezoelectric acoustic body 11. For example, by replacing the wiring connecting the control unit 13 and the piezoelectric acoustic body 11 with the wiring connecting the control unit 13 and the piezoelectric acoustic body 11, the same effect as that obtained by changing the configuration of the control unit 13 can be obtained. it can. The input / output relationship between the control unit 13 and the piezoelectric acoustic bodies 11 and 12 may be manually switched. As described above, according to the transmitted sound reducing device according to the first embodiment, the two piezoelectric acoustic bodies can be interchanged by switching the role as a microphone for noise detection and the role as a control speaker. Can easily cope with the noise.

  The piezoelectric acoustic bodies 11 and 12 preferably have the same acoustic characteristics. Specifically, it is preferable that the piezoelectric acoustic bodies 11 and 12 have the same characteristics as a microphone (see FIG. 2) and the generated sound pressure characteristics (see FIG. 3). Since the piezoelectric acoustic bodies 11 and 12 have the same acoustic characteristics, the controller 13 can be easily designed. When the piezoelectric acoustic bodies 11 and 12 have the same acoustic characteristics, the filter characteristics of the control section 13 are changed before and after the replacement even if the input / output relationship between the control section 13 and the piezoelectric acoustic bodies 11 and 12 is switched. There is no need. That is, the control unit 13 does not need to prepare two types of filters according to the direction in which noise comes.

  In addition, the transmitted sound reduction device according to Embodiment 1 can be installed on a wide range of wall surfaces by connecting a plurality of the devices. FIG. 9 is a cross-sectional view of a noise reduction panel in which a plurality of transmitted sound reduction apparatuses according to Embodiment 1 are connected. Fig.9 (a) is a front view of a noise reduction panel, FIG.9 (b) is AB sectional drawing of a noise reduction panel. In FIG. 9A, the control unit 13 is not shown for the purpose of making the drawing easier to see. The noise reduction panel shown in FIG. 9A is configured to have a panel-like form by connecting nine transmitted sound reduction devices 91 by connection portions 92. This noise reduction panel can be used by being installed inside a wall or the like. Each transmitted sound reducing device 91 has the same configuration as the transmitted sound reducing device shown in FIG. Although FIG. 9 shows a noise reduction panel in which three vertical and three horizontal transmitted sound reduction devices are connected side by side, a panel having a wider area by connecting more transmitted sound reduction devices. Can also be realized.

  When the transmitted sound reducing device is actually installed on the wall, it is conceivable to attach the noise reducing panel as described above to a predetermined range of the wall. The range in which the noise reduction panel is attached to the wall may be attached to the entire surface of the wall, or may be attached to a range in which noise is easily transmitted. The range through which noise can easily pass can be determined by calculating the contribution rate, for example. The contribution rate is an index indicating the ratio of noise transmitted through the portion of the noise that propagates in the space surrounded by walls (the space where noise should be reduced). In this case, the noise transmitted in the space can be efficiently reduced by arranging the noise reduction panel in a portion where the contribution ratio is high.

  The control unit 13 may be any configuration as long as it has a characteristic that satisfies the expression (5), in addition to the signal inverting amplifier. The control unit 13 can be configured by an analog circuit or a digital circuit.

(Embodiment 2)
Next, a transmitted sound reducing apparatus according to Embodiment 2 will be described. The transmitted sound reducing device according to the second embodiment further improves the sound insulation performance of the transmitted sound reducing device according to the first embodiment. In the second embodiment, two transmitted sound reduction devices are installed side by side along the direction in which noise propagates. As a result, the sound insulation effect is applied to the noise twice to improve the sound insulation performance.

  FIG. 10 is a cross-sectional view of the transmitted sound reducing apparatus according to the second embodiment. In FIG. 10, the transmitted sound reducing device includes four piezoelectric acoustic bodies 101 to 104, a connection unit 105, and two control units 106 and 107. The piezoelectric acoustic bodies 101 and 102 and the control unit 106 constitute a first transmitted sound reducing device. The piezoelectric acoustic bodies 103 and 104 and the control unit 107 constitute a second transmitted sound reducing device. The first and second transmitted sound reducing devices perform the same operation as the transmitted sound reducing device according to the first embodiment. That is, the transmitted sound reducing device according to the second embodiment has a configuration in which two transmitted sound reducing devices according to the first embodiment are connected. The first and second transmitted sound reducing devices are connected by the connection unit 105. A space is formed by the connecting portion 105, the piezoelectric acoustic body 102, and the piezoelectric acoustic body 103. This space is preferably sealed so that noise does not leak outside. In the second embodiment, the first and second transmitted sound reducing devices are connected along the direction in which noise is transmitted.

  Next, the operation of the transmitted sound reducing apparatus according to the second embodiment will be described. Here, a case where noise comes from the left to the right (toward the page) will be described. First, in the first transmitted sound reducing apparatus, the piezoelectric acoustic body 102 is used as a microphone for noise detection. The piezoelectric acoustic body 101 operates as a control speaker. The control method in control unit 106 is the same as in the first embodiment. The noise transmitted from the left side of the paper surface is reduced by the first transmitted sound reducing device. The reduced noise propagates through the space inside the connecting portion 105 and passes through the second transmitted sound reducing device.

  In the second transmitted sound reducing apparatus, the piezoelectric acoustic body 104 is used as a noise detection microphone, and the piezoelectric acoustic body 103 is used as a control speaker. Therefore, the second transmitted sound reducing device can reduce the noise transmitted through the second transmitted sound reducing device by performing the same operation as the first transmitted sound reducing device. As described above, in the second embodiment, the sound insulation action is performed twice with respect to the noise.

で定まる。なお、（６）式において、λは長辺の長さｂと短辺の長さａとから定まる無次元パラメータ、２ｈは板厚、Ｅはヤング率、νはポアソン比、ρは密度である。（６）式より、長方形平板の第１次共振周波数はその面積に反比例するので、圧電音響体の面積を変化させることによって第１次共振周波数を変化させることができる。従って、圧電音響体１０１および１０２の振動板面積と、圧電音響体１０３および１０４の振動板面積とを異なるように設計すれば、第１の透過音低減装置によって低減可能な周波数帯域と、第２の透過音低減装置によって低減可能な周波数帯域とを異なるように設計することができる。すなわち、１つの透過音低減装置を用いる場合に比べて広い周波数帯域の騒音を低減することができる。 As described in the first embodiment, the first and second transmitted sound reducing apparatuses can reduce only noise in a predetermined frequency band. Here, when the frequency band that can be reduced by the first transmitted sound reducing device and the frequency band that can be reduced by the second transmitted sound reducing device are different from each other, when one transmitted sound reducing device is used. Compared with this, noise in a wider frequency band can be reduced. That is, the primary resonance frequency of the piezoelectric acoustic body (piezoelectric acoustic bodies 101 and 102) used in the first transmitted sound reducing device and the piezoelectric acoustic body (piezoelectric acoustic body 103 and piezoelectric acoustic body used in the second transmitted sound reducing device). If the first resonance frequency of 104) is designed to be different, noise in a wider frequency band can be reduced. Here, according to the “Handbook of Mechanical Engineering” (edited by the Japan Society of Mechanical Engineers, 1987), the primary resonance frequency of the rectangular plate whose periphery is fixed is:

Determined by In equation (6), λ is a dimensionless parameter determined from the length b of the long side and the length a of the short side, 2h is the plate thickness, E is the Young's modulus, ν is the Poisson's ratio, and ρ is the density. . From the equation (6), the primary resonance frequency of the rectangular flat plate is inversely proportional to the area thereof, so that the primary resonance frequency can be changed by changing the area of the piezoelectric acoustic body. Therefore, if the diaphragm area of the piezoelectric acoustic bodies 101 and 102 and the diaphragm area of the piezoelectric acoustic bodies 103 and 104 are designed to be different, the frequency band that can be reduced by the first transmitted sound reducing device, and the second The frequency band that can be reduced by the transmitted sound reducing device can be designed to be different. That is, noise in a wide frequency band can be reduced as compared with the case where one transmitted sound reducing device is used.

  As described above, according to the second embodiment, it is possible to realize a transmitted sound reduction device having noise reduction performance in a wider frequency band than in the first embodiment. In the above description, the case where the first resonant frequency of the first transmitted sound reducing device is designed to be different from the first resonant frequency of the second transmitted sound reducing device has been described. You may design so that the primary resonant frequency of a sound reduction device may be made the same. In this case, the rate of noise reduction in a predetermined frequency band can be increased as compared with the first embodiment.

  In the second embodiment, as in the first embodiment, the transmitted sound reducing device can be applied to a wider range of wall surfaces by connecting a plurality of transmitted sound reducing devices side by side.

(Embodiment 3)
Next, a transmitted sound reducing apparatus according to Embodiment 3 will be described. In the transmitted sound reducing apparatus according to the first embodiment, the frequency band of noise that can be reduced is fixed, and the frequency band of noise to be reduced cannot be changed. The transmitted sound reduction apparatus according to Embodiment 3 can change the frequency band of noise that can be reduced.

  FIG. 11 is a cross-sectional view of the transmitted sound reducing apparatus according to the third embodiment. In FIG. 11, the transmitted sound reducing device includes piezoelectric acoustic bodies 11 and 12, a control unit 13, and cases 111 and 112. The piezoelectric acoustic bodies 11 and 12 and the control unit 13 are the same components as those in the first embodiment. The third embodiment is a configuration further including casings 111 and 112 in addition to the components of the first embodiment. The casing 111 includes a cylindrical member 113 and a movable wall 114. Similarly, the housing 112 includes a cylindrical member 115 and a movable wall 116.

  The cylindrical member 113 has a cylindrical shape with both ends opened, and the cross-sectional shape parallel to the opening surface is the same as the piezoelectric acoustic bodies 11 and 12. One end of the opening of the cylindrical member 113 is connected to the piezoelectric acoustic body 11. The cylindrical member 113 has a plurality of slits for attaching the movable wall 114 on its inner peripheral surface. The movable wall 114 is a flat plate having a size suitable for being inserted into the slit on the inner peripheral surface of the cylindrical member 113. The movable wall 114 is connected to the cylindrical member 113 by being inserted into any of the plurality of slits of the cylindrical member 113. Note that the housing 112 has the same configuration as the housing 111. One end of the opening of the cylindrical member 115 of the housing 112 is connected to the piezoelectric acoustic body 12. The movable wall 116 is a flat plate having the same shape as the movable wall 114. The movable wall 116 is inserted into any of the plurality of slits of the cylindrical member 115.

  With the above configuration, the transmitted sound reduction device according to Embodiment 3 can change the mounting position of the movable wall. FIG. 12 is a diagram illustrating a state in which the movable wall of the transmitted sound reducing device illustrated in FIG. 11 is moved. In FIG. 12, for the sake of easy understanding, the cylindrical member 113 is not shown, and only the piezoelectric acoustic body 11 and the movable wall 114 are shown. Moreover, the dotted line shown by FIG. 12 shows the slit provided in the cylindrical member 113. FIG. The movable wall 114 is fixed to the cylindrical member 113 by being inserted into any of the slits provided in the cylindrical member 113. As a result, a space surrounded by the casing 111 and the piezoelectric acoustic body 11 is formed. This space is preferably a sealed space. The volume of this space can be changed by changing the position where the movable wall 114 is inserted.

  The configurations of the casings 111 and 112 are not limited to the above, and any configuration can be used as long as it is connected to the piezoelectric acoustic body and can form a sealed space having a variable volume with the piezoelectric acoustic body. It may be a simple configuration.

  FIG. 13 is a diagram showing the relationship between the volume of the space surrounded by the housing and the like and the sound pressure frequency characteristic of the piezoelectric acoustic body. In FIG. 13, the size of the space surrounded by the housing or the like is changed in three stages, and the sound pressure frequency characteristics in each case are shown. The solid line shown in FIG. 13 is the sound pressure frequency characteristic when the size of the space is the smallest. The dashed-dotted line shown in FIG. 13 is the sound pressure frequency characteristic when the size of the space is the second smallest. The dotted line shown in FIG. 13 is the sound pressure frequency characteristic when the space is the largest. As shown in FIG. 13, the primary resonance frequency increases as the space is reduced, and the primary resonance frequency decreases as the space is increased. Therefore, it is possible to obtain a desired first resonance frequency by changing the volume of this space as described above. Similarly to the piezoelectric acoustic body 11, the piezoelectric acoustic body 12 can obtain a desired primary resonance frequency by changing the volume of the space surrounded by the housing 112, the piezoelectric acoustic body 12 and the movable wall 114. Is possible.

  As described above, in Embodiment 3, the primary resonance frequency of the piezoelectric acoustic body can be changed. Further, as described in the first embodiment, the frequency band of noise that can be reduced by the transmitted sound reducing device varies depending on the primary resonance frequency of the piezoelectric acoustic body. Therefore, according to the third embodiment, the user can freely change the frequency band of noise to be reduced.

  In the third embodiment, similarly to the first embodiment, the transmitted sound reducing device can be applied to a wider range of wall surfaces by connecting a plurality of transmitted sound reducing devices side by side.

(Embodiment 4)
Next, a transmitted sound reducing apparatus according to Embodiment 4 will be described. In the transmitted sound reducing devices according to the first to third embodiments described above, it is possible to easily deal with noise from both directions, but manually when dealing with noise from the opposite direction. Had to change settings. In the fourth embodiment, the transmitted sound reduction device automatically detects the direction in which noise arrives, and can automatically cope with noise from both directions.

  FIG. 14 is a diagram illustrating a transmitted sound reducing device according to the fourth embodiment. In FIG. 14, piezoelectric acoustic bodies 11 and 12, a control unit 13, and a determination unit 141 are provided. FIG. 14 is a configuration obtained by adding a determination unit 141 to the configuration illustrated in FIG. 1, and the components other than the determination unit 141 are the same as those in the first embodiment. The determination unit 141 is connected to the piezoelectric acoustic bodies 11 and 12. The determination unit 141 is connected to the control unit 13.

  Next, the operation of the transmitted sound reducing apparatus according to the fourth embodiment will be described focusing on the operation of the determination unit 141. FIG. 15 is a flowchart showing the flow of processing of the determination unit shown in FIG. In the fourth embodiment, the control unit 13 is not driven immediately when the transmitted sound reducing device is operated by turning on the power of the transmitted sound reducing device or the like. At this time, the piezoelectric acoustic bodies 11 and 12 are both set to operate as noise detecting microphones. Each noise signal detected in the piezoelectric acoustic bodies 11 and 12 is output to the determination unit 141.

  On the other hand, when the transmitted sound reducing device is driven, the determination unit 141 first inputs noise signals detected in the piezoelectric acoustic bodies 11 and 12 (step S1). Next, the determination unit 141 compares the noise signal level N1 detected in the piezoelectric acoustic body 11 with the noise signal level N2 detected in the piezoelectric acoustic body 11. Specifically, it is determined whether or not || N1 ||> | N2 || (step S2). That is, in step S2, the determination unit 141 determines from which direction the noise comes (in FIG. 14, whether the noise comes from the right side or the left side of the page). In step S2, if || N1 ||> | N2 ||, it is determined that the noise comes from the piezoelectric acoustic body 11 side (the right side of the paper). On the contrary, when || N1 || = <|| N2 ||, it is determined that noise comes from the piezoelectric acoustic body 12 side (left side of the paper).

  In step S2, if || N1 ||> | N2 ||, the determination unit 141 operates the piezoelectric acoustic body 11 as a control speaker and the piezoelectric acoustic body 12 as a noise detection microphone. Set (step S3). Specifically, an input / output setting signal indicating an instruction to operate the piezoelectric acoustic body 11 as a control speaker and the piezoelectric acoustic body 12 as a noise detection microphone is output to the control unit 13. In response to the input / output setting signal, the control unit 13 inputs a noise signal from the piezoelectric acoustic body 12 and controls the piezoelectric acoustic body 11 based on the input noise signal. This control is the same as that of the transmitted sound reducing apparatus shown in FIG.

  On the other hand, if || N1 || = <|| N2 || in Step S2, the determination unit 141 operates the piezoelectric acoustic body 12 as a control speaker and the piezoelectric acoustic body 11 as a noise detection microphone. (Step S4). Specifically, an input / output setting signal indicating an instruction to operate the piezoelectric acoustic body 12 as a control speaker and the piezoelectric acoustic body 11 as a noise detection microphone is output to the control unit 13. In response to the input / output setting signal, the control unit 13 inputs a noise signal from the piezoelectric acoustic body 11 and controls the piezoelectric acoustic body 12 based on the input noise signal. This control is the same as that of the transmitted sound reducing apparatus shown in FIG.

  Here, the control unit 13 performs filtering so that the piezoelectric acoustic body 11 is operated as a noise detection microphone and the piezoelectric acoustic body 12 is operated as a control speaker and vice versa. Prepare two. Then, the filter to be used is switched according to the content of the input / output setting signal from the determination unit 141. That is, the control unit 13 switches the filter to be used according to the direction in which noise is transmitted. As described above, the piezoelectric acoustic body can be controlled so as to reduce the noise regardless of which direction the noise comes from.

  In addition, it is preferable to use the piezoelectric acoustic bodies 11 and 12 having the same acoustic characteristics. When having the same acoustic characteristic, the signal transmission characteristic P to the other when one piezoelectric acoustic body is driven is the same. Therefore, in this case, equation (5) can be satisfied using the same filter regardless of the direction in which the noise arrives. For example, when the piezoelectric acoustic body 11 and the piezoelectric acoustic body 12 are configured by the same piezoelectric speaker, the control unit 13 does not need to prepare two types of filters according to the direction in which noise comes.

  After step S3 or S4, the determination unit 141 determines whether a predetermined time has elapsed (step S5). The predetermined time is a time predetermined in the determination unit 141. If it is not determined in step S5 that the predetermined time has elapsed, the process of step S4 is repeated. On the other hand, if it is determined in step S5 that the predetermined time has elapsed, the process returns to step S1. That is, the determination unit 141 waits until a predetermined time elapses, and when the predetermined time elapses, returns to the process of step S1 and repeats the processes of steps S1 to S4.

  Through the processing in step S4, the transmitted sound reducing device can detect from which direction the noise is coming from every predetermined time. Accordingly, noise can be reliably reduced even in an environment where the direction in which the noise comes from moment to moment changes.

  As described above, according to the fourth embodiment, it is possible to automatically cope with noise coming from both directions. Further, by detecting the direction of noise arrival at a predetermined time interval, it is possible to cope with a change in the direction of noise arrival.

  In addition, the transmitted sound reduction device may further include a display device serving as a display. At this time, the determination unit 141 displays the determination result of the determination unit 141 on the display device. As a result, the transmitted sound reducing device can be used as a device for determining the direction in which noise arrives.

  In the fourth embodiment, the determination unit 141 automatically determines which direction the noise coming from is reduced, but in other embodiments, the determination unit 141 receives the noise. The user may be notified that the direction or direction of arrival has changed. Then, in accordance with the notification, the user determines from which direction the noise coming from is reduced. At this time, the transmitted sound reduction device needs to include an input unit that receives input from the user. Further, at this time, the control unit 13 determines which direction the noise comes from in accordance with a user instruction received by the input unit. In addition, as a specific method of notification, the user may be notified by sound, or when the above-described display device is provided with the transmitted sound reduction device, display may be performed on the display device.

  Also, in the fourth embodiment, similarly to the first embodiment, the transmitted sound reducing device can be applied to a wider range of wall surfaces by connecting a plurality of transmitted sound reducing devices side by side. At this time, it is not necessary to provide a plurality of determination units 141, and only one determination unit 141 may be provided. When the number of determination units 141 is one, the determination unit 141 outputs input / output setting signals having the same contents to the control units of the plurality of transmitted sound reduction devices.

  In the fourth embodiment, the configuration in which the determination unit 141 is further added to the configuration in the first embodiment has been described. However, the configuration in which the determination unit 141 is further added to the configurations in the second and third embodiments may be used. Good. Even in such a configuration, the operation of the determination unit 141 is the same as the operation described in the fourth embodiment.

  In the first to fourth embodiments, the piezoelectric acoustic body has been described as an example of the electroacoustic transducer. However, the electroacoustic transducer is not limited to a piezoelectric acoustic body, and any electroacoustic transducer may be used as long as it has a vibration surface and can detect sound by the vibration surface. In addition, the electroacoustic transducer must be configured so that there is no shielding on both sides of the vibration surface so that sound from both sides of the vibration surface can be detected in the same way and sound can be emitted in the same way on both sides of the vibration surface. Is preferred.

  As described above, the transmitted sound reducing device according to the present invention can be used for the purpose of realizing a small-scale configuration and easily dealing with noise coming from both directions.

The figure which shows the transmitted sound reduction apparatus which concerns on Embodiment 1. FIG. The figure which shows the characteristic as a microphone of the piezoelectric speaker used in Embodiment 1 The figure which shows the characteristic (generated sound pressure characteristic) of the sound pressure which the piezoelectric speaker generates The figure which shows the transmitted sound reduction apparatus in the case of implement | achieving the control part 13 shown in FIG. The figure which shows the PC characteristic of the transmitted sound reduction apparatus shown in FIG. The figure which shows the evaluation apparatus for evaluating the performance of the transmitted sound reduction apparatus shown in FIG. The figure which shows the frequency characteristic of the noise detected with the microphone 65 in the case where the transmitted sound reduction apparatus 61 is not driven and the case where it drives using the evaluation apparatus shown in FIG. The figure which shows the transmitted sound reduction apparatus in the environment where noise arrives from the direction opposite to FIG. Sectional drawing of the noise reduction panel which connected multiple transmitted sound reduction apparatuses which concern on Embodiment 1. FIG. Sectional drawing of the transmitted sound reduction apparatus which concerns on Embodiment 2. FIG. Sectional drawing of the transmitted sound reduction apparatus which concerns on Embodiment 3. FIG. The figure which shows a mode that the movable wall of the transmitted sound reduction apparatus shown in FIG. 11 is moved. The figure which shows the relationship between the volume of the space enclosed by housing | casing etc. and the sound pressure frequency characteristic of a piezoelectric acoustic body The figure which shows the transmitted sound reduction apparatus which concerns on Embodiment 4. FIG. The flowchart which shows the flow of a process of the determination part shown in FIG. The figure which shows the conventional transmitted sound reduction device The figure which shows the detailed structure of the cell 162 shown in FIG.

Explanation of symbols

11, 12, 101, 102, 103, 104 Piezoelectric acoustic bodies 13, 106, 107 Control unit 14 Signal inversion amplifier 92 Support unit 105 Connection units 111, 112 Case

Claims (11)

A transmitted sound reducing device that reduces noise that arrives from a predetermined direction and propagates through its own device,
A first electroacoustic transducer that detects noise, converts the detected noise into an electrical signal, and outputs the electrical signal;
A second electroacoustic transducer having a vibration surface disposed opposite the vibration surface of the first electroacoustic transducer and emitting sound to the vibration surface of the first electroacoustic transducer;
A first control unit that controls driving of the second electroacoustic transducer based on the electrical signal so that the level of the electrical signal output from the first electroacoustic transducer is attenuated; Transmitted sound reduction device. When noise arrives from a direction opposite to the predetermined direction, the second electroacoustic transducer detects the noise, converts the detected sound into an electric signal, and outputs it.
The first control unit controls driving of the first electroacoustic transducer based on the electrical signal so that the electrical signal output from the second electroacoustic transducer is attenuated,
2. The transmitted sound reduction device according to claim 1, wherein the first electroacoustic transducer emits sound to a vibration surface of the second electroacoustic transducer according to control by the first control unit. The detection result of noise by the first and second electroacoustic transducers is input, and based on the detection result, it is determined whether the noise comes from the predetermined direction or the reverse direction. A determination unit;
When the determination unit determines that noise comes from the predetermined direction, the first control unit drives the second electroacoustic transducer based on a detection result of the first electroacoustic transducer. And when the determination unit determines that the noise comes from the opposite direction, the driving of the first electroacoustic transducer is controlled based on the detection result of the second electroacoustic transducer. The transmitted sound reducing device according to claim 2.   The transmitted sound reduction apparatus according to claim 3, wherein the determination unit performs determination at a predetermined time interval. A first housing connected to a vibration surface of the first electroacoustic transducer and forming a sealed space having a variable volume between the vibration surface and the vibration surface;
The transmission according to claim 1, further comprising: a second housing connected to a vibration surface of the second electroacoustic transducer and forming a sealed space having a variable volume between the vibration surface and the vibration surface. Sound reduction device.   The transmitted sound reduction device according to claim 1, wherein the first electroacoustic transducer has the same electroacoustic transduction characteristics as the second electroacoustic transducer.   The transmitted sound reduction apparatus according to claim 1, wherein the first control unit includes a signal inverting amplifier.   The transmitted sound reduction device according to claim 1, wherein the first and second electroacoustic transducers are flat plate type piezoelectric acoustic bodies. A third electroacoustic transducer that detects noise, converts the detected noise into an electrical signal, and outputs the electrical signal;
A fourth electroacoustic transducer, the vibration surface of which is disposed opposite to the vibration surface of the third electroacoustic transducer and emits sound to the vibration surface of the third electroacoustic transducer;
A second control unit that controls driving of the fourth electroacoustic transducer based on the electrical signal so that the electrical signal output from the third electroacoustic transducer is attenuated;
The transmitted sound reduction device according to claim 1, further comprising a connection portion that forms a sealed space between the first electroacoustic transducer and the fourth electroacoustic transducer. The primary resonance frequency of the first and second electroacoustic transducers is set to the same value,
The primary resonance frequencies of the third and fourth electroacoustic transducers are set to the same value,
The primary resonance frequency of the first and second electroacoustic transducers is set to a value different from the primary resonance frequency of the third and fourth electroacoustic transducers. Noise control device. A noise control panel configured by the transmitted sound reduction device according to claim 1,
A plurality of the transmitted sound reducing devices;
A support portion for supporting the outer periphery of the first and second electroacoustic transducers of each transmitted sound reducing device,
Each of the transmitted sound reducing devices is a noise control panel that is connected by the support portion in a direction substantially parallel to the vibration surfaces of the first and second electroacoustic transducers.

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