JP5153697B2 - Noise suppression device and vending machine - Google Patents

Description

  The present invention relates to a noise suppression device and a vending machine, and more specifically, suppresses noise leaking from each opening provided in a front surface and a rear surface of a housing that houses a noise source and has a rear surface facing a wall surface. It relates to technology.

  2. Description of the Related Art Conventionally, there is known an active noise reduction technique for detecting noise generated by a noise source with a microphone and outputting a sound having a phase opposite to that of the noise from a speaker to reduce the noise. Active silencing is a method of adjusting the gain and phase for each frequency component of noise detected by a microphone to generate a speaker drive signal, and can output a control sound for canceling noise from the speaker.

  Recently, vending machines with an active silencing function that reduce the leakage of noise generated from an internal noise source to the outside have been proposed (for example, Patent Documents 1 and 2). Normally, a vending machine has a cooling fan for cooling the heat exchanger in the housing, and a front panel with a product selection switch is provided with a vent for inhaling air. Has been. The air sucked into the casing from the vent is sent backward by the cooling fan, and is discharged to the outside from the vent on the rear face of the casing.

  In the case of such a vending machine, there has been a problem that noise generated by the cooling fan leaks to the outside through the vent. Therefore, a conventional vending machine with an active silencing function has a front microphone and a front speaker installed on the front panel, and the front speaker is driven based on an input signal from the front microphone, thereby the front of the housing The noise that leaks to the outside from the vents of the air was reduced. Also, a rear microphone and a rear speaker are installed on the rear side of the housing, and the rear speaker is driven based on an input signal from the rear microphone, thereby leaking outside from the vent on the rear of the housing. To reduce the noise.

JP 2008-210342A JP 2008-210343 A

  By the way, in general, the vending machine is often installed with the back side of the casing close to a wall surface such as a building so as not to obstruct the passage. In this case, the rear microphone installed on the rear side of the vending machine's housing also reflects the reflected sound of the noise reflected from the wall and entering through the vent on the back of the housing, in addition to the direct sound from the noise source. Will be entered.

  The intensity and phase of the reflected sound vary depending on the surface condition of the wall surface, the distance between the back of the housing and the wall surface, and the like. For this reason, it is difficult to specify the direct sound from the sound collected by the rear microphone, and there is a problem that the direct sound cannot be sufficiently canceled.

  The present invention has been made in view of the above circumstances, and it is possible to install a device that accommodates a noise source and has openings on the front and back surfaces of the housing, particularly the back surface close to the wall surface. An object of the present invention is to provide a noise suppression device and a vending machine capable of effectively suppressing noise leaking to the outside from an opening on the back surface of a casing.

  A noise suppression device according to a first aspect of the present invention is a noise suppression device that suppresses noise leaking from each opening provided in a front surface and a rear surface of a housing that houses a noise source and has a rear surface facing a wall surface. A front speaker and a microphone disposed in front of the noise source; a rear speaker disposed in the rear of the noise source; and the front speaker and the rear speaker based on an output signal of the microphone. And a control unit that suppresses noise leaking from the two openings.

  According to such a configuration, based on the output signal of the microphone arranged in front of the noise source, the rear speaker arranged behind the noise source is driven and leaks from the opening on the rear surface of the housing. Noise can be suppressed. For this reason, in order to install a device equipped with a noise suppression device in the vicinity of the wall surface, even if the back of the casing of the device is opposed to the wall surface, noise is not affected by the reflected sound from the wall surface. It can be effectively suppressed.

  In addition to the above configuration, the noise suppression device according to the second aspect of the present invention is configured such that the control unit includes a phase difference adjusting unit that adjusts a phase difference between sounds output from the front speaker and the rear speaker. . In general, the phase difference of noise propagating in the reverse direction from the same noise source is constant, and the distance difference from the noise source to the front speaker and the rear speaker is also constant. For this reason, by adjusting the phase difference between the sound output from the front speaker and the rear speaker, when the sound is effectively silenced by the front speaker, the sound muffing by the rear speaker is also effective. It can be carried out.

  According to a third aspect of the present invention, in addition to the above-described configuration, the noise source includes a rotationally movable portion that performs rotational motion, and the front speaker and the rear speaker output sounds having substantially opposite phases. Configured to do. In the case of a noise source having a rotationally movable part that performs rotational movement, such as a cooling fan, noise that propagates in the opposite direction from the noise source has an opposite phase. For this reason, when the difference in distance from the noise source to the front speaker and the rear speaker is sufficiently small compared to the wavelength of the noise, if the sound output from the front speaker and the rear speaker is substantially in phase, the housing Noise leaking from the opening on the back of the body can also be effectively suppressed.

  A vending machine according to a fourth aspect of the present invention is equipped with the above-described noise suppression device. According to such a configuration, based on the output signal of the microphone arranged in front of the noise source, the rear speaker arranged behind the noise source is driven and leaks from the opening on the rear surface of the housing. Noise can be suppressed. For this reason, even when the vending machine's back is facing the wall surface in order to install the vending machine in the vicinity of the wall surface, noise is effectively prevented without being affected by the reflected sound from the wall surface. Can be suppressed.

  The noise suppression device and the vending machine according to the present invention drive the front speaker and the rear speaker based on the output signal of the microphone arranged in front of the noise source, and are respectively provided on the front surface and the back surface of the housing. Noise that leaks from the opening is suppressed. As a result, even if the rear surface of the casing of the device is opposed to the wall surface in order to install the device equipped with this noise suppression device near the wall surface, the noise is not affected by the reflected sound from the wall surface. Can be effectively suppressed. Moreover, since such active silencing is realized with a simple configuration, a noise suppression device can be provided at low cost.

  Further, the vending machine according to the present invention drives the front speaker and the rear speaker based on the output signal of the microphone arranged in front of the noise source, and has openings provided on the front and rear surfaces of the casing, respectively. The noise leaking from the part is suppressed. For this reason, even when the back of the housing is opposed to the wall surface in order to install this vending machine in the vicinity of the wall surface, noise is effectively suppressed without being affected by the reflected sound from the wall surface. Can do. In addition, since such active silencing is realized with a simple configuration, a vending machine can be provided at low cost.

It is the figure which showed an example of schematic structure of the apparatus carrying the noise suppression apparatus by embodiment of this invention, and the vending machine 100 is shown as an example of such an apparatus. It is the figure which showed the state which opened the front panel 2 of the vending machine 100 of FIG. It is sectional drawing of the vending machine 100 of FIG. 1, and the cut surface by the AA line of FIG. 1 is shown. It is sectional drawing of the vending machine 100 of FIG. 1, and the cut surface by the BB line of FIG. 1 is shown. It is the figure which showed an example of the operation | movement in the vending machine 100 of FIG. 1, and the analysis result which analyzed the cross spectrum between the front channel and the back channel is shown. It is the block diagram which showed the structural example of the noise suppression apparatus 110 mounted in the vending machine 100 of FIG. It is the figure by which the observation points P11-P13, P21-P23, and P31-P33 of the sound arrange | positioned ahead of the vending machine 100 were shown. It is the figure which showed the experimental result about the wraparound of the noise from the back of the vending machine 100 to the front. It is the figure which showed an example of the silence operation in the vending machine 100 of FIG. 1, and the observation result observed by varying the phase difference between the front and rear speakers is shown. It is the figure which showed an example of the silencing operation | movement in the vending machine 100 of FIG. 1, and the case where the distance from the back panel 3 to a wall surface is 10 mm is shown. It is the figure which showed an example of the silencing operation | movement in the vending machine 100 of FIG. 1, and the case where the distance from the back panel 3 to a wall surface is 50 mm is shown. FIG. 2 is a diagram showing an example of a silencing operation in the vending machine 100 of FIG. 1, and shows a case where no wall surface exists behind the back panel 3. It is the figure which showed an example of the silencing operation in the vending machine 100 of FIG. 1, and the observation result in case the phase difference of the front and rear speakers is 195 ° is shown. It is the figure which showed an example of the silencing operation | movement in the vending machine 100 of FIG. 1, and the observation result of the silencing effect observed by varying the gain difference between front and back speakers is shown.

  FIG. 1 is an external view showing an example of a device equipped with a noise suppression device according to an embodiment of the present invention. A vending machine 100 is shown as an example of a device equipped with a noise suppression device. (A) in the figure shows a state in which the vending machine 100 is viewed from the front direction, and (b) shows a state in which the vending machine 100 is viewed from the side direction. FIG. 2 is a view showing a state in which the front panel 2 of the vending machine 100 of FIG. 1 is opened. FIG. 3 is a cross-sectional view of the vending machine 100 of FIG. 1, and shows a cut surface taken along the line AA of FIG. Hereinafter, the left side in FIGS. 1B and 3 will be described as the front, and the right side will be described as the rear.

  The vending machine 100 is a vending machine that sells beverages enclosed in cans or PET bottles as products, and a large number of products are accommodated in the housing 1. The housing 1 has a rectangular parallelepiped shape having a front panel 2 and a back panel 3 facing each other. The housing 1 is formed with an opening that opens the entire front surface, and a front panel 2 that covers the opening is attached to the housing 1 so as to be openable and closable. Legs 4 are attached to the bottom surface of the housing 1.

  In the front center portion of the front panel 2, a money insertion portion 5 used when a user who wants to purchase a product inserts money is formed. A coin insertion slot 5A for inserting coins, a bill insertion slot 5B for inserting bills, and a return lever 5C for instructing the return of the inserted coins are inserted into the money insertion section 5. An input amount display portion 5D for displaying the total amount of money is provided.

  A display unit 7 on which samples of merchandise are displayed is formed on the upper front portion of the front panel 2. The display unit 7 is provided with a plurality of product selection switches 7A associated with each sample on display. The operation switch 7A is an operation means for selecting a product, and the user purchases a product corresponding to the selection switch 7A by operating one of the product selection switches 7A after inserting money. be able to. The product for which purchase is instructed is sent out to the lower part in the housing 1 and can be taken out from a horizontally long product outlet 8 formed in the lower part of the front panel 2.

  A money handling unit 28 is provided at the center of the back surface of the front panel 2. The money handling unit 28 stores money inserted from the coin insertion slot 5A and the bill insertion slot 5B, and performs processing of returning money from the coin return slot 6 or the bill insertion slot 5B as necessary. A control unit 13 that controls the operation of the vending machine 100 is provided on the right side of the money handling unit 28.

  In the housing 1, a product housing portion 21 for housing a product is formed in an area extending from the center to the upper portion, and in the front of the housing 1 from the product housing portion 21 to the product outlet 8 side. A product discharge port 22 for discharging the product is formed.

  In the lower part of the housing 1, a cooler 24 that cools the product stored in the product storage unit 21, a compressor 27 that compresses the refrigerant supplied to the cooler 24, and the compressed refrigerant is liquefied. A heat exchanger 25, a cooling fan 26 for cooling the heat exchanger 25, and the rear speaker 12 are disposed.

  A horizontally long vent 2H is formed at the bottom of the front panel 2, and a vent 3H is also formed at the bottom of the back panel 3. The vent 2H and the vent 3H are openings that allow the inside and outside of the housing 1 to communicate with each other, and air sucked from the outside through the vent 2H is discharged to the outside through the vent 3H. The back panel 3 is installed on the opposite side of the front panel 2 across noise sources such as the cooling fan 26 and the compressor 27, and the vending machine 100 is arranged with the back panel 3 facing the wall surface.

  The cooling fan 26 is an axial fan that sends the air sucked back through the vent 2H provided in the front panel 2 to the rear, and generates airflow by rotating propeller blades with an electric motor. ing. The compressor 27 is a rotary piston type compressor, and compresses the refrigerant by rotating the rotary piston with an electric motor.

  A partition plate 23 is provided below the product accommodating portion 21, and a duct-like space that penetrates the housing 1 in the front-rear direction is formed below the partition plate 23. The heat exchanger 25, the cooling fan 26, and the compressor 27 are arranged in this duct space.

  A microphone 10 and a front speaker 11 are disposed at the lower part of the front panel 2. The microphone 10 is an input device that converts sound generated by a noise source such as the cooling fan 26 or the compressor 27 into an electric signal. The front speaker 11 is an output device that outputs a control sound having an opposite phase to the noise emitted from the vent 2H of the front panel 2 to the outside. Here, the microphone 10 and the front speaker 11 are disposed from the back surface of the front panel 2 toward the duct-shaped space. However, it is only necessary that the microphone 10 and the front speaker 11 be disposed at least in front of the noise source. For example, you may arrange | position from the front lower part of the front panel 2 toward the exterior.

  The rear speaker 12 is installed in the housing 1 behind the noise source such as the cooling fan 26 and the compressor 27, and is a control sound having an opposite phase to the noise emitted from the vent 3H of the rear panel 3 to the outside. Is an output device. Here, the rear speaker 12 is disposed around the duct-shaped space toward the duct-shaped space. However, the rear speaker 12 may be disposed at least behind the noise source. For example, the rear speaker 12 is disposed in the duct-shaped space. It may be installed on the back panel 3.

  Next, the active mute function will be described. The active silencing function drives the front speaker 11 and the rear speaker 12 based on the input signal from the microphone 10, and generates noise generated from the cooling fan 26 and the compressor 27 in the vending machine 100 to the front speaker 11 and the rear speaker. This is a function to mute by the control sound output from the speaker 12 for use.

  FIG. 4 is a cross-sectional view of the vending machine 100 of FIG. 1, and shows a cut surface taken along line BB of FIG. The back panel 3 is installed on the opposite side of the front panel 2 across a noise source such as the cooling fan 26, and the vending machine 100 is arranged with the back panel 3 facing the wall surface.

  The cooling fan 26 is a blower that generates airflow by rotating propeller blades, and sends out the air sucked in through the vent 2H provided in the front panel 2 to the rear. The front speaker 11 is disposed in front of the cooling fan 26 toward the cooling fan 26, and the rear speaker 12 is disposed on the opposite side of the front panel 2 with respect to the cooling fan 26. The rear speaker 12 is positioned so that the sound source center is located behind the cooling fan 26.

  The noise generated from the cooling fan 26 is mainly noise having a frequency corresponding to the number of blade rotations and the number of blades, and this noise propagates forward and rearward of the cooling fan 26. The sound that propagates forward from the cooling fan 26 and the sound that is output from the front speaker 11 are input to the microphone 10. By causing the front speaker 11 to output a sound having a phase opposite to the sound propagating forward from the cooling fan 26, the noise propagating forward from the cooling fan 26 can be silenced.

  FIG. 5 is a diagram showing an example of the operation in the vending machine 100 of FIG. 1, in which an analysis result obtained by analyzing the cross spectrum between the detection signal by the front microphone and the detection signal by the rear microphone is shown. Yes. The front microphone is an observation microphone arranged in front of the cooling fan 26, and the rear microphone is an observation microphone arranged behind the cooling fan 26.

  (A) in the figure shows the power spectrum of the detection signal of the front microphone, and (b) shows the phase difference of the detection signal of the rear microphone with respect to the front microphone.

  In the power spectrum of the detection signal of the front microphone, a peak point E1 having the maximum power exists in the vicinity of a frequency of 85 Hz. The phase difference between the detection signal of the rear microphone and the front microphone is calculated by cross spectrum analysis between the front and rear detection signals. The phase difference in the vicinity of the peak point E1 is stable and is in a steady state E2 of approximately −185 ° (deg).

  In other words, the cooling fan 26 generates sound with opposite phases before and after, and the phase of the optimally controlled output with respect to the front speaker 11 is reversed, and the distance between the front speaker 11 and the cooling fan 26 and the rear speaker are reversed. If a correction amount corresponding to the difference between the distance between the cooling fan 26 and the cooling fan 26 is added and output from the rear speaker 12, the noise propagating backward from the cooling fan 26 can be effectively silenced.

In the example of FIG. 4, the length D1 in the left-right direction of the housing 1 is 1000 mm, the length D2 in the front-rear direction is 640 mm, the distance D3 between the microphone 10 and the front speaker 11 is 260 mm, the front speaker 11 and the cooling fan 26. The distance D4 between them is 200 mm, and the distance D5 between the rear speaker 12 and the cooling fan 26 is 240 mm. If the noise of the cooling fan 26 has a peak of intensity in the vicinity of frequency = 85 Hz and the speed of sound is 340 m, the wavelength λ = 4000 mm. Therefore, the control sound of the rear speaker 12 is rearward using the rear speaker 12 if the phase difference is adjusted so that the phase difference α with respect to the control sound of the front speaker 11 satisfies the following equation (1). Propagating noise can also be silenced.
α = (D4-D5) / λ × 360 ° -180 ° (1)

  In this example, the phase difference α = (200−240) /4000×360°−180°=−183.6°, and according to the distance difference (D4−D5) and the wavelength λ of the sound to be silenced, The value is slightly deviated from the reverse phase (−180 °).

  In this way, the phase difference α between the front speaker 11 and the rear speaker 12 can be obtained from the noise wavelength λ and the difference in distance from the noise source to each speaker 11, 12. Instead of calculating the phase difference α, the operator may determine the value of the phase difference α having a high silencing effect while manually adjusting the phase difference α. In this way, if an appropriate phase difference α is obtained, when the effective noise reduction is performed by the front speaker 11, the effective noise reduction is also performed by the rear speaker 12. The adjustment work of the loudspeaker 12 is facilitated.

  FIG. 6 is a block diagram showing a configuration example of the noise suppression device 110 mounted on the vending machine 100 of FIG. The noise suppression device 110 includes a microphone 10, a front speaker 11, a rear speaker 12, an amplifier 35, and a control unit 13. The control unit 13 is a control device that drives the front speaker 11 and the rear speaker 12 based on the output signal of the microphone 10, and includes a control sound generation unit 31, gain adjustment units 32 and 34, and a phase adjustment unit 33. The

  Based on the output signal of the microphone 10, the control sound generation unit 31 generates a control sound signal for suppressing noise leaking outside from the vent 2 </ b> H of the front panel 2, and the gain adjustment unit 32 and the phase adjustment unit 33. To output to. The control sound signal is a drive signal for adjusting the phase and intensity of the sound output from the front speaker 11 with reference to the sound input to the microphone 10. The phase and intensity adjustment values are set in advance in consideration of the difference between the distance between the front speaker 11 and the cooling fan 26 and the distance between the microphone 10 and the cooling fan 26. With this control sound signal, it is possible to cause the front speaker 11 to output a control sound having an opposite phase to the noise transmitted forward from the cooling fan 26.

  The gain adjusting unit 32 has a function of adjusting the gain of the control sound signal from the control sound generating unit 31 and increasing the gain by ΔG1 compared to the output of the microphone 10 and outputting the gain to the front speaker 11.

  The phase adjustment unit 33 outputs the phase of the control sound signal from the control sound generation unit 31 by the phase difference α in order to cause the rear speaker 12 to output a sound substantially in reverse phase to the sound output from the front speaker 11. This is a phase difference adjusting means for the control sound that is phase-shifted and output to the gain adjusting unit. Specifically, the phase adjustment is performed so that the phase difference α with respect to the sound output from the front speaker 11 satisfies the relational expression (1) described above.

  The gain adjusting unit 34 has a function of adjusting the gain of the control sound signal from the phase adjusting unit 33, increasing the gain by ΔG 2 as compared with the output of the microphone 10, and outputting the gain to the rear speaker 12.

  The gain adjustment by the gain adjustment units 32 and 34 can be performed independently, and the adjustment values ΔG1 and ΔG2 are set in advance so that the silencing effect by the control sound output from the front speaker 11 and the rear speaker 12 is maximized. Is set. An amplifier 35 having a constant gain is provided between the gain adjustment unit 32 and the front speaker 11 and between the gain adjustment unit 34 and the rear speaker 12.

  7 to 13 are diagrams relating to experiments for verifying the silencing effect by the vending machine 100 of FIG. The present inventors conducted various experiments in order to verify the silencing effect of the vending machine 100 of FIG. The contents and results of these experiments will be described in detail with reference to FIGS.

  7 and 8 are explanatory diagrams of experiments for verifying the sneaking of noise leaked from the back surface toward the front of the vending machine 100. FIG. In FIG. 7, nine sound observation points P11 to P13, P21 to P23, and P31 to P33 arranged in front of the vending machine 100 are shown. Observation points P11 to P13 are observation points 1 m away from the vending machine in the front direction, and are located at heights of 1.5 m, 1.0 m, and 0.5 m from the installation surface of the vending machine, respectively. ing. Observation points P21 to P23 are observation points that are 1 m away from the front direction at an angle of 45 ° to the left (45 ° left), and observation points P31 to P33 are an oblique right direction at an angle of 45 ° to the front direction (45 ° to the right). ), The height is the same as that of the observation points P11 to P13.

  FIG. 8 is a diagram showing an experimental result of noise wraparound from the rear to the front of the vending machine 100. (A) in the figure shows the observation results when the front speaker 11 and the rear speaker 12 are muted, and (b) is muted using only the front speaker 11. The observation results are shown. These observation results show the silencing effect in dB when neither the front speaker 11 nor the rear speaker 12 is used.

  Needless to say, when only the front speaker 11 is used, the silencing effect is reduced as compared with the case where both the front and rear speakers 11 and 12 are used. However, it can be seen from this observation result that even with the front speaker 11 alone, a certain degree of silencing effect is obtained at a low position in the front direction, but the silencing effect is greatly reduced at a high position in the front direction. It can also be seen that the silencing effect is further greatly reduced in the diagonally left direction and diagonally right direction. In other words, if only the front speaker 11 is used and the rear speaker 12 is not used, the noise leaked from the vent 3H circulates in front of the vending machine 100, thereby sufficiently increasing the noise level in front of the vending machine 100. It cannot be suppressed.

  In the case of a conventional vending machine, if there is a wall in the vicinity of the back panel 3, the microphone installed behind the noise source has not only the direct sound from the noise source but also the reflected sound reflected by the wall surface. Is also entered. For this reason, in the conventional vending machine, the noise leaked to the outside from the vent 3H of the back panel 3 cannot be sufficiently silenced. Therefore, it is conceivable that the rear speaker 12 is simply stopped and only the front speaker 11 is operated. However, from the above experimental results, when only the front speaker 11 is used, the front of the vending machine 100 is sufficient. The mute effect cannot be obtained.

  On the other hand, in the vending machine 100 according to the present embodiment, the front speaker 11 and the rear speaker 12 are driven based on the input signal from the microphone 10 provided on the front panel 2 to face the wall surface. Noise leaking from the vent 3H can also be effectively suppressed. For this reason, in the conventional vending machine, it turns out that the silencing effect is high compared with the case where the rear speaker 12 is stopped and only the front speaker 11 is operated.

  FIG. 9 is a diagram showing an example of the silencing operation in the vending machine 100 of FIG. 1, and shows the silencing effect observed by changing the phase difference between the front and rear speakers 11 and 12 in both directions around 180 °. Observation results are shown. In the figure, the triangle mark indicates the observation result at the observation point P1 in the diagonally left direction, the circle mark indicates the observation result at the observation point P2 in the front direction, and the square mark indicates the observation result at the observation point P3 in the diagonally right direction. ing.

  The sound output from the rear speaker 12 is substantially opposite in phase to the sound output from the front speaker 11, and the phase difference is centered at 180 °, and the distance D 4 between the front speaker 11 and the cooling fan 26. And the difference between the distance D5 between the rear speaker 12 and the cooling fan 26 is adjusted.

  From this experimental result, the vending machine in FIG. 1 has a silencing effect of 10 dB or more at any observation point P1 to P3 in the range C1 where the phase difference between the front and rear speakers is 175 ° to 200 °. It turns out that an effect becomes the maximum.

  10 to 12 are diagrams showing an example of the silencing operation in the vending machine 100 of FIG. 1, and show the results of the silencing effect observed by varying the distance to the wall surface. FIG. 10 shows a case where the distance from the back panel 3 to the wall surface is 10 mm. In this case, in the range C2 where the phase difference between the front and rear speakers 11 and 12 is 190 ° or more and 210 ° or less, there is a silencing effect of 10 dB or more for any of the observation points P1 to P3.

  FIG. 11 shows a case where the distance from the back panel 3 to the wall surface is 50 mm. In this case, in the range C3 where the phase difference between the front and rear speakers is 185 ° or more and 205 ° or less, there is a silencing effect of 10 dB or more for any of the observation points P1 to P3.

  FIG. 12 shows a case where there is no wall surface behind the back panel 3. In this case, in the range C4 where the phase difference between the front and rear speakers is 175 ° or more and 205 ° or less, there is a silencing effect of 10 dB or more for any of the observation points P1 to P3.

  From the observation results of FIG. 10 to FIG. 12, in the range where the phase difference between the front and rear speakers 11 and 12 is 175 ° to 200 °, any observation point P1 to P3 has a silencing effect of 5 dB or more. The silencing effect is higher than when only the front speaker 11 is operated in the apparatus. In particular, when the phase difference is around 195 °, the lateral silencing effect is high.

  FIG. 13 is a diagram showing an example of the silencing operation in the vending machine 100 of FIG. 1, and shows the observation result when the phase difference between the front and rear speakers is 195 °. (A) in the figure shows a case where the distance from the back panel 3 to the wall surface is 10 mm, and (b) shows a case where no wall surface exists behind the back panel 3.

  Except for the observation result at the height = 1.5 m when the distance to the wall surface is 10 mm and the observation result at the height = 0.5 m, there is a silencing effect of 10 dB or more in each case, and the front direction A high silencing effect is obtained in both the horizontal direction and the horizontal direction.

  FIG. 14 is a diagram showing an example of the silencing operation in the vending machine 100 of FIG. 1, and shows the observation result of the silencing effect observed by varying the gain difference between the front and rear speakers around 0. Yes. In this figure, an observation point 45 ° diagonally left with respect to the front direction of the vending machine 100 is P1, an observation point in the front direction is P2, and an observation point 45 ° diagonally to the right is P3. The observation result obtained by changing the gain of the rear speaker 12 when the phase difference is fixed at 180 ° is shown.

  When the gain difference between the front and rear speakers is near 0, there is a silencing effect of 10 dB or more at any observation point P1 to P3, and the silencing effect is maximized.

  According to the present embodiment, the front speaker 11 and the rear speaker 12 are driven based on the output signal of the microphone 10 provided on the front panel 2, and noise transmitted from a noise source such as the cooling fan 26 is transmitted to these speakers. Therefore, when the vending machine 100 is placed close to the wall surface of the building, the noise is not affected by the reflected sound of the noise entering from the vent 3H of the rear panel 3. Can be reduced.

  In the present embodiment, an example of a vending machine incorporating a cooling fan or a compressor as a noise source has been described, but the present invention is not limited to such a case. That is, the present invention can also be applied to various devices including a noise source, such as a refrigerator and a personal computer. In addition, the present invention is suitable for a device having a built-in noise source that performs a rotational motion, such as a cooling fan or a compressor. However, the noise source is not limited to a cooling fan or a compressor, and may be a device that performs a rotational motion. It is not limited.

  Further, in the present embodiment, an example in the case of suppressing the noise in the antiphase between the front and the rear has been described, but the present invention is not limited to such a case, and the antiphase is set in the front and the rear. The present invention can also be applied to a device that suppresses unwanted noise. For example, when a noise source that generates noise of the same phase at the front and rear of the noise source is accommodated in the housing, by setting an adjustment value of the phase proportional to the distance difference (D4-D5), Noise that leaks to the outside from the vent can be suppressed.

DESCRIPTION OF SYMBOLS 100 Vending machine 110 Noise suppression apparatus 1 Case 2 Front panel 2H Vent 3 Rear panel 3H Vent 4 Leg 5 Coin slot 6 Coin return 7 Display unit 8 Product outlet 10 Microphone 11 Front speaker 12 For back Speaker 13 Control unit 21 Product accommodation unit 22 Product discharge port 23 Partition plate 24 Cooler 25 Heat exchanger 26 Cooling fan 27 Compressor 28 Money processing unit 31 Control sound generation unit 32 Gain adjustment unit 33 Phase adjustment unit 34 Gain adjustment unit 35 Amplifier

Claims (4)

A noise suppression device that contains a noise source and suppresses noise leaking from each opening provided in the front and back surfaces of the housing with the back surface facing the wall surface,
A front speaker and a microphone arranged in front of the noise source;
A rear speaker disposed behind the noise source;
A noise suppression apparatus comprising: a control unit that drives the front speaker and the rear speaker based on an output signal of the microphone to suppress noise leaking from the two openings.   2. The noise suppression device according to claim 1, wherein the control unit includes a phase difference adjusting unit that adjusts a phase difference between sounds output from the front speaker and the rear speaker. The noise source has a rotationally movable part that performs rotational motion,
The noise suppression device according to claim 1, wherein the front speaker and the rear speaker output sounds having substantially opposite phases.   An automatic vending machine comprising the noise suppression device according to any one of claims 1 to 3.

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