JP2925540B1 - Noise reduction system for machinery - Google Patents

Abstract

Abstract: PROBLEM TO BE SOLVED: To attenuate directional control for eliminating noise due to ultra-low sound generated from a plurality of mechanical devices having a vibration source such as a motor and a beat sound caused thereby and attenuating sound pressure in a designated direction. Provide mechanical equipment. SOLUTION: A programmable controller (PLC) 41 measures a vibration frequency of each mechanical device based on output signals of displacement sensors 13 and 23 provided in the mechanical devices 11 and 21, respectively, and the vibration frequencies of both mechanical devices are equal. A rotation speed instruction signal of the motor 22 is sent to the inverter 26 so that the rotation speed becomes constant. The beating sound is eliminated by this feedback control. Further, the PLC 41 appropriately changes the rotation speed instruction signal sent to the inverter 26 so that the mechanical devices 11 and 21 vibrate at a phase difference angle at which the sound pressure level at a place (direction) where the noise problem should be solved becomes low. I do.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system for reducing noise (secondary vibration) due to ultra-low sound (generally, sound having a frequency of 20 Hz or less) generated from a plurality of mechanical devices.

[0002]

2. Description of the Related Art In many cases, a large vibrating sieve is used as a mechanical device for separating and dewatering solids in muddy water in the construction of a muddy pressurized shield, but the ultra-low sound generated from the vibrating sieve is treated as a noise problem. May be In other words, the vibrating sieve has a motor installed in
It rotates at 000 rpm, and its rotational force is transmitted to the eccentric weight shaft of the machine and vibrates. The vibration at that time causes air to vibrate the fittings of a house or the like, which causes complaints.

[0003] One of the conventional measures against noise is sound insulation. That is, a completely closed room is formed of a rigid material such as concrete, which surrounds the noise source. However, for example, in subway construction, it is extremely difficult to form a completely closed room because an opening for carrying out separated and dewatered earth and sand is required. On the other hand, there is a method in which noise is absorbed by a sound absorbing device using a resonator or the like, but this method is not suitable as a measure against ultra-low sound. In other words, since the ultra-bass has a very long wavelength,
To absorb this, a large-scale resonator must be used, leading to an increase in construction costs. In addition, since underground work is performed in a small space, it is difficult to install a large-scale resonator, and even if it can be installed, other works will be hindered.

[0004] Further, in large section shield works such as subway works, the number of vibrating screens used is plural. In this case, if a slight difference occurs between the vibration frequencies of the individual mechanical devices, the sounds generated from the respective vibrating screens interfere with each other to generate an ultra-low sound. As a countermeasure against this, it is conceivable to provide a large difference between the vibration frequencies of the individual vibrating screens. However, doing so causes a variation in the amount of work to be processed and makes maintenance and management difficult.

As a method of solving the beat phenomenon, there is a method of directly connecting the eccentric weight shafts of two vibrating sieves and mechanically operating the vibrating sieves at a phase difference angle of 180 °. According to this method, the beat phenomenon is eliminated, but the usual noise problem due to the vibration of the mechanical device is not completely eliminated. This will be described below with reference to FIGS. FIGS. 5 to 8 are diagrams showing sound pressure distributions generated from two sound sources having phase difference angles of 0 °, 90 °, 180 ° and 270 °, respectively. In these figures, solid circles indicate peaks of sound pressure generated by each sound source, and broken circles indicate valleys. Where the solid circle and the dashed circle intersect, the peaks and valleys of the sound pressure generated by both sound sources overlap and cancel each other, so the sound pressure decreases,
No noise problem. On the other hand, where solid circles or dashed circles are close to each other, peaks or valleys overlap, so that the sound pressure level increases. According to the above method, the sound pressure distribution is as shown in FIG. 7, and the sound pressure increases on a straight line passing through the two sound sources due to interference. Therefore, if a general house or the like exists in the direction of this straight line, there is a high possibility that the above-described problem will occur there.

[0006]

As described above, among the noise countermeasures, in particular, with respect to the attenuation countermeasures against ultra-low sound, it is difficult to solve them by the conventional general techniques of sound insulation and sound absorption. Also, if multiple machines are operated at the same time,
A beat phenomenon due to an ultra-low sound occurs, and the influence of noise is further increased. The present invention has been made to solve such a problem, and an object of the present invention is to eliminate noises caused by a plurality of mechanical devices, particularly, ultra-low noises, and further, to prevent beat noises caused by the noises, and to specify the noises. It is an object of the present invention to provide an inexpensive mechanical device capable of performing attenuation directivity control for attenuating sound pressure in a direction.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a sound pressure generated by a plurality of mechanical devices including a vibration source and a vibrator driven by the vibration source. A noise reduction system for changing a level distribution, comprising: a vibration detecting unit that detects vibration of a vibrating body of each mechanical device and outputs a signal corresponding to the frequency of the vibration; A driving frequency changing unit for changing a driving frequency of the vibration source, and a vibration frequency of a vibrating body of the first mechanical device is detected as a target frequency based on an output signal of the vibration detecting unit, and another mechanical device is detected. So that the vibration frequency of the vibrating body is equal to the target frequency,
Control means for controlling a drive frequency of a vibration source of each mechanical device through the drive frequency changing means.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The noise reduction system according to the present invention does not use the same drive frequency (motor rotation speed) of the vibration source (eg, motor) of each mechanical device as in the prior art. Vibration detecting means for detecting vibration of the driven vibrating body (for example, vibrating sieve) itself is provided for each mechanical device, and control is performed such that the vibration frequencies of the vibrating bodies detected by these vibration detecting means are all equal. There is a feature in what you do.

In the present invention, for example, the vibration detecting means is configured to detect a displacement of a predetermined portion of the vibrating body and generate an electric signal corresponding to the displacement. Such a vibration detection means, an optical sensor, a known sensor such as a magnetic sensor is installed at an appropriate place near or above the vibrating body,
The vibration frequency is determined based on the relationship between the amplitude of the electric signal output from the sensor and time. The drive frequency changing means changes the drive energy (for example, the drive voltage of the motor) supplied to the vibration source of each mechanical device in accordance with a predetermined input signal, and utilizes, for example, an inverter circuit or the like controlled by a microcomputer. This can be configured. The control means comprises, for example, a programmable memory (E
It can be configured using an electronic circuit including an EPROM, a personal computer, or the like.

As a preferred embodiment of the noise reduction system according to the present invention, a sound pressure distribution for detecting a sound pressure level in a space where the plurality of mechanical devices are installed at a plurality of locations and outputting a signal corresponding to the sound pressure level. Measuring means, performing a filtering process on the output signal of the sound pressure distribution measuring means,
A filter for extracting data of a sound pressure level in a predetermined frequency band; and a filter between the vibration of the vibrating body of the first mechanical device and the vibration of the vibrating body of another mechanical device based on an output signal of the vibration detecting means Phase difference angle calculation means for calculating a phase difference angle between, and storage means for storing data of the sound pressure level distribution in the predetermined frequency band and the phase difference angle in association with each other, the control means, Controlling the drive frequency changing means so that the phase difference angle calculated by the phase difference angle calculation means during operation of the plurality of mechanical devices is a phase difference angle corresponding to a desired sound pressure level distribution. Noise reduction system.

In the noise reduction system of the above-described embodiment, the filter processing is, for example, processing for measuring a sound pressure level in a frequency band including a sound having a frequency of about 16 Hz, which easily causes a noise problem in an ultra-low sound range. As a means for performing such processing, a commonly used octave analyzer can be suitably used.

[0012]

As described above, the noise reduction system according to the present invention appropriately changes the drive frequency of the vibration source of each mechanical device based on the output signal of the vibration detecting means for detecting the vibration of the vibrating body itself of the mechanical device. Therefore, the vibration frequencies of the vibrators of all the mechanical devices can be matched with high accuracy without being affected by the structural characteristics of the mechanical devices, and the beat noise can be effectively eliminated. Further, the noise reduction system according to the preferred embodiment of the present invention can reduce the sound pressure level at a desired place or direction by appropriately changing the phase difference angles of the vibrations of the plurality of vibrators. This has a great effect on solving the ultra-low sound noise problem.

[0013]

FIG. 1 is a block diagram showing a schematic configuration of an embodiment of a noise reduction system according to the present invention. The noise reduction system of the present embodiment is installed for the purpose of reducing the noise generated from the three mechanical devices 11, 21 and 31. The mechanical devices 11, 21 and 31 utilize a sieving effect by vibrating the mechanical devices by rotating eccentric shafts (not shown) by motors 12, 22 and 32 (vibrating sieve). In such a mechanical device, even if the rotational speeds of the motors 12, 22 and 32 are controlled to be the same, the structural characteristics of each mechanical device are different. The mechanical device does not always vibrate, so that it is not possible to reliably eliminate ultra-low or humming sounds.

In view of this, the noise reduction system of the present embodiment employs a configuration in which the displacement sensors 13, 23, and 33 provided for each of the mechanical devices 11, 21, and 31 directly measure the vibration frequency and amplitude of the mechanical device. doing. This will be described below using the mechanical device 11 as an example.

That is, the displacement sensor 13 is
And irradiates a predetermined portion of the mechanical device 11 with light in parallel with the vibration direction of the mechanical device 11, and outputs a voltage signal according to the intensity of light reflected from the portion. In addition,
The relationship between the voltage between the mechanical device 11 and the displacement sensor 13 and the voltage is checked in advance. For example, the displacement sensor 13
5 volts when the distance from to the mechanical device 11 is 10 cm, and 0 volt when the distance is 20 cm. The voltage signal is amplified by the amplifier 14 and sent to the V / P converter 15. The V / P converter 15 outputs a pulse signal to the high-speed counter unit 40 at the point where the mechanical device 11 comes closest to the displacement sensor 13 (the point where the voltage is the highest in the voltage signal). The vibrations of the mechanical devices 21 and 31 are also detected by the displacement sensors 23 and 33, the amplifiers 24 and 34, and the V / P converters 25 and 35, and a pulse signal corresponding to the vibration is output to the high-speed counter unit 40.

The pulse signals output from the V / P converters 15, 25 and 35 are also sent to a personal computer (PC) 43 via an A / D converter 42. An input device (keyboard, mouse, etc.) 44 for the user to input control commands, control data, and the like is connected to the personal computer 43.

The high-speed counter unit 40 detects a pulse signal output from a V / P converter provided in each mechanical device, and sends a signal indicating the detection time to a programmable controller (PLC) 41 having an arithmetic unit. PL
When C41 receives the signal, the arithmetic unit digitally calculates the vibration frequency and stores the value in a memory in the arithmetic unit. Further, the PLC 41 is connected via the D / A converter 45 to
Inverters 16, 26 and 3 provided for each mechanical device
6, and sends a signal (rotation speed instruction signal) for instructing the rotation speed of the motor of each mechanical device to each inverter. Each inverter drives the corresponding motor of the mechanical device based on the rotation speed instruction signal.

The control for equalizing the vibration frequencies of the two mechanical devices 11 and 21 by the above-described noise reduction system of the present embodiment will be described with reference to FIG. In addition,
FIG. 2 is a flowchart showing a vibration control method of a mechanical device in the noise reduction system.

First, the user operates the input device 44,
Various control variables (in this embodiment, the target phase difference angle θ1, the motor rotation speed B0, and the phase difference angle error allowable value θcal) are input to the personal computer 43 (step S10). Here, the motor rotation speed B0 is the initial rotation speed of the motor when each mechanical device is started. Θ1 and θcal will be described later. The control variables set in this way are sent from the personal computer 43 to the PLC 41 and stored in the memory of the PLC 41.

When the setting of the variables is completed as described above, P
The LC 41 sends a rotation speed instruction signal (B0) to the inverters 16 and 26. Thus, the operation of the mechanical devices 11 and 21 is started at the rotation speed B0 of the motors 12 and 22 (step S12). Thereafter, as described above, the PLC 41 measures the time intervals (pulse intervals) S0 and S1 at which the pulse signals are output from the V / P converter 15 (V1) and the V / P converter 25 (V2) (Step S).
14, S16). S0 and S1 obtained in this way correspond to the vibration cycle of the mechanical devices 11 and 21.

When the two oscillation periods S0 and S1 are obtained, the PLC 41 checks the magnitude of S0 and S1.
That is, if S0 is larger than S1 (the determination result is "Y" in step S18), it is smaller than the vibration frequency (= 1 / S0) of the mechanical device 11 (= 1 / S1). Means larger. Therefore, the PLC 41 sends a rotation speed instruction signal to the inverter 26 such that the rotation speed of the motor 22 of the mechanical device 21 is reduced by an appropriate amount in order to equalize the vibration frequencies of the two mechanical devices (step S19). Conversely, if S0 is smaller than S1 (the determination result is "Y" in step S20), the PLC
41 sends a rotation speed instruction signal to the inverter 26 to increase the rotation speed of the motor 22 of the mechanical device 21 by an appropriate amount (step S21). The amount by which the rotation speed of the motor 22 is increased / decreased is determined by the difference between S1 and S0 (or 1 / S0).
(The difference between S0 and 1 / S1).

After the rotation speed of the motor 22 is changed as described above, the process returns to steps S14 and S16 for measuring the vibration cycle of each mechanical device. As a result of such feedback control, the vibration frequencies of the mechanical devices 11 and 21 become equal, and the generation of beat noise is prevented. When the vibration frequencies of the two mechanical devices 11 and 21 become equal, PLC
41 stores the value D1 of the output signal (rotation speed instruction signal) to the inverter 26 at that time in the memory (step S22).

A series of steps subsequent to step S22 corresponds to control (attenuation directing control) for maintaining the phase difference angle of vibration of the mechanical devices 11 and 21 constant. The reason why such control is necessary is explained as follows. That is, as described above, when two sound sources are arranged, the variation in the sound pressure distribution generated around the two sound sources changes according to the phase difference angle between the waves generated by the two sound sources. Therefore,
Conversely, by maintaining the phase difference angle between the two waves at an appropriate value, it is possible to maintain a low sound pressure level at a desired location. Therefore, such a phase difference angle θ
1 is obtained in advance, the value is stored in the memory of the PLC 41 (step S10), and control is performed such that the phase difference angle is always equal to θ1 during the operation of the mechanical device.

The attenuation directivity control is performed as follows.
That is, following step S22, the PLC 41
Based on the output signal of the high-speed counter unit 40, V1
The output time interval S2 between the pulse signal from V2 and the pulse signal from V2 is measured (step S24), and based on the value, the phase difference angle at that time (current phase difference angle) θ2
From the following equation: θ2 = S2 × 360 ° / S0
(1) (Step S2)
6). For example, if the time from when the pulse of V1 is transmitted to when the pulse of V2 is transmitted is 30 msec, and the vibration period S0 of the mechanical device 11 is 60 msec, 30 msec × 3
The calculation result of 60 ° / 60 msec = 180 °, that is, the result that the vibration of the mechanical device 11 and the vibration of the mechanical device 21 are in opposite phases is obtained.

When the value of θ2 is obtained, the PLC 4
1 digitally calculates the error (= θ2−θ1) of θ2 from the previously set target phase difference angle θ1, and the absolute value of the error is larger than the previously set phase difference angle error allowable value θcal. It is determined whether or not (step S28). At this time,
If the absolute value of the error is not more than θcal, it is determined that a good sound pressure distribution can be maintained only by fine adjustment of the phase difference angle,
Proceed to step S30. On the other hand, if the absolute value of the error is larger than θcal, the process returns to step S14.

The steps after step S30 are as follows. First, the PLC 41 performs steps S30 and S32.
And an error is evaluated, and a rotation speed instruction signal D2 determined according to the result is sent to the inverter 26. That is, θ2 is θ
If greater than 1 (the determination result is “Y” in step S30)
In order to make them equal, it is necessary to reduce the vibration period S2 of the mechanical device 21 (see equation (1)).
Therefore, the PLC 41 provides a rotation speed instruction signal D2 for reducing the rotation speed of the motor 22 of the mechanical device 21 by an appropriate amount.
Is sent to the inverter 26 (step S31). Conversely, θ
When 2 is smaller than θ1 (when the determination result is “Y” in step S32), the PLC 41 sends a rotation speed instruction signal D2 to the inverter 26 to increase the rotation speed of the motor 22 by an appropriate amount (step S33).

After the phase difference angle is adjusted by temporarily changing the rotation speed of the motor 22, the rotation speed instruction signal D1 previously stored in the memory in step S22 is sent to the inverter 26 again. Output (Step S3
4). If the result of the determination in step S32 is "N", since θ2 is equal to θ1, it is not necessary to adjust the phase difference angle, and the control proceeds directly to step S34.

The reason for returning to step S14 when the error of the phase difference angle is larger than θcal in step S28 is explained as follows. That is, in the above vibration control, the vibration frequency of the mechanical device 11 is targeted, and the vibration frequency of the mechanical device 21 is made to follow it. However, in the muddy water pressure shielding work, the amount of work to be processed by the mechanical device is always constant. Not quantity. For this reason, the mechanical device 11
May fluctuate, and the target vibration frequency may change. Further, when the driving force of the motor is transmitted by a V-belt instead of driving the mechanical device directly by the motor, the slip angle of the V-belt in one mechanical device changes the phase difference angle of vibration between the two mechanical devices. Sometimes. In such a case, the phase difference angle cannot be quickly restored to the target value (θ1) by the fine adjustment of the phase difference angle by the attenuation directivity control after step S28 described above. Therefore,
The process once returns to step S14 and executes the above-described steps (steps S14 to S22) again, thereby quickly correcting the vibration frequency and the phase difference angle. As a result, it is possible to quickly respond in real time to a change in the vibration state caused by a load change or the like.

Next, a method of controlling the sound pressure level with higher accuracy by using a low frequency sound pressure level meter will be described. As shown in FIG. 1, the noise reduction system according to the present embodiment includes a low-frequency sound pressure level meter 5 arranged at three different points (for example, three points X, Y, and Z shown in FIG. 3).
1 to 53 are provided. These low-frequency sound pressure level meters detect sound pressure in a frequency band of 0 to 100 Hz and output a signal corresponding to the sound pressure. In this embodiment, these signals are further analyzed by octave. By inputting it to the unit 54 and performing 1/3 octave analysis,
A sound pressure level (particularly, a 16 Hz band) in a specific frequency band mainly including an ultra-low sound generated from a mechanical device is extracted.

The sound pressure level data of the target frequency band thus extracted is sent to the personal computer 43. PC 43
Stores the sound pressure level data at each point and the phase difference angle θ2 at that time in a storage unit (memory, hard disk, or the like) (not shown) in association with the sound pressure level data. Such processing is executed at a step angle of 10 ° over an angle range of, for example, 0 ° to 350 °, and the sound pressure levels of all 36 patterns are related to the phase difference angle, and the sound pressure level decreases in a desired direction. Such an optimum phase difference angle is determined. Of course, it is also possible to control the phase difference angle with a finer step angle as needed. Needless to say, the greater the number of low-frequency sound pressure level meters, the more accurately the sound pressure distribution can be grasped.

As described above, the signal of the sound pressure level analyzed by the octave analyzer 54 is digitally output, and
3 side, and the sound pressure distribution at each phase difference angle is grasped, and an appropriate phase angle (0 ° to 3 °) is set on the personal computer 43 side so as to minimize the ultra-low sound pressure level at a point where a noise problem occurs.
50 °), and this angle is set as the target phase difference angle θ1 and P
By sending it to the LC 41, the noise problem is eliminated.

Even if the ultra-low sound pressure level does not fall below a certain level even in a series of processes up to this point, the noise reduction system of the present embodiment takes measures to change the vibration frequency itself of the target mechanical device 11. be able to. Although it has been described that the rotation speed of the mechanical device is normally 1000 rpm, in the present embodiment, the inverter 16 is also installed in the mechanical device 11 serving as a reference for the vibration frequency control, and the motor 1
2 can be changed in a range of about 200 rpm. If the rotation speed of the motor 12 is changed in this way, the vibration frequency of the mechanical device 11 naturally changes. The vibration frequency of the mechanical device 21 is
By following the one vibration frequency, the frequency band of the ultra-low sound generated from these mechanical devices can be changed. By taking advantage of this fact, if the frequency band of the ultra-low sound generated from the mechanical device is appropriately changed so as not to include natural frequencies such as windows and sashes which are likely to cause secondary vibration, noise due to the secondary vibration can be reduced. Eliminate problems.

The vibration frequency of the third mechanical device 31 can be made to follow the first mechanical device 11 by the above-described method, so that the phase difference angle between the two vibrations can be maintained at the target phase difference angle. Needless to say. Needless to say, even if the number of mechanical devices is four or more, the noise reduction system of the present invention can be used. Further, according to the present invention, the plurality of mechanical devices do not necessarily need to be installed adjacent to each other, and can be arranged according to the situation.

FIG. 4 is a diagram showing an example of a format for displaying various data on a display (not shown) of the personal computer 43. In this example, the vibration state (amplitude change) of each mechanical device
Table showing sound pressure level values obtained by octave analysis of sound pressure levels measured by low-frequency sound pressure level meters 51 to 53 arranged at three points (X, Y, Z).
And the reference mechanical device 11 (in FIG. 4, the mechanical device No.
1) and other mechanical devices 21 and 31 (mechanical device No. 2 in FIG. 4).
And No. 3) are shown on the display. In this way, the effect of the noise reduction control can be confirmed at a glance.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of an embodiment of a noise reduction system according to the present invention.

FIG. 2 is a flowchart showing a vibration control method of a mechanical device in the noise reduction system.

FIG. 3 is a layout diagram of three low-frequency sound pressure level meters.

FIG. 4 is an exemplary view showing an example of a format for displaying various data on a display of a personal computer.

FIG. 5 is a diagram showing a sound pressure distribution generated by two sound sources having a phase difference angle of 0 °.

FIG. 6 is a diagram showing a sound pressure distribution generated by two sound sources having a phase difference angle of 90 °.

FIG. 7 is a diagram showing a sound pressure distribution generated by two sound sources having a phase difference angle of 180 °.

FIG. 8 is a diagram showing a sound pressure distribution generated by two sound sources having a phase difference angle of 270 °.

[Explanation of symbols]

 11, 21, 31 ... Machinery 12, 22, 32 ... Motor 13, 23, 33 ... Displacement sensor 16, 26, 36 ... Inverter 40 ... High-speed counter unit 41 ... Programmable controller (PLC) 43 ... Personal computer (PC) 51 ~ 53 ... Low frequency sound pressure level meter 54 ... Octave analyzer

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Satoshi Yamamoto 1-3-15 Awaza, Nishi-ku, Osaka Kashima Construction Co., Ltd.Kansai Branch (72) Inventor Kinmitsu Nakayama 1-3-15 Awaza, Nishi-ku, Osaka Kashima Construction Inside Kansai Branch Co., Ltd. (72) Inventor Tetsuki Kikuchi 1-3-15 Awaza, Nishi-ku, Osaka Kashima Construction Co., Ltd. Kansai Branch Co., Ltd. (56) References JP-A-5-188978 (JP, A) (58) Survey Field (Int.Cl. ⁶ , DB name) G10K 11/178

Claims (2)

(57) [Claims] 1. A noise reduction system for changing a sound pressure level distribution due to an ultra-low sound generated from a plurality of mechanical devices including a vibration source and a vibrating body driven by the vibration source. Vibration detecting means for detecting a vibration of the vibrating body and outputting a signal corresponding to the frequency of the vibration; a driving frequency changing means for changing a driving frequency of a vibration source provided in each mechanical device; Based on the output signal of the vibration detecting means, the vibration frequency of the vibrating body of the first mechanical device is detected as a target frequency, and the driving is performed so that the vibration frequency of the vibrating body of another mechanical device becomes equal to the target frequency. Control means for controlling a drive frequency of a vibration source of each mechanical device through frequency changing means. 2. A sound pressure distribution measuring means for detecting sound pressure levels at a plurality of locations in a space where the plurality of mechanical devices are installed, and outputting a signal corresponding to the sound pressure levels, and the sound pressure distribution measuring means. Filter means for performing filter processing on the output signal of the above, and extracting data of the sound pressure level in a predetermined frequency band, vibration of the vibrating body of the first mechanical device based on the output signal of the vibration detection means Phase difference angle calculation means for calculating a phase difference angle between the vibration of the vibrating body of another mechanical device, and storage for storing data of the sound pressure level distribution in the predetermined frequency band and the phase difference angle in association with each other. Means, wherein the control means is configured such that the phase difference angle calculated by the phase difference angle calculation means during operation of the plurality of mechanical devices is a phase difference angle corresponding to a desired sound pressure level distribution. Drive Noise reduction system according to claim 1, characterized in that to control the wave number changing means.