JPS61109495A - Silence controlling method of low frequency sound - Google Patents

Abstract

PURPOSE:To effectively silence a low frequency sound from two sets of low frequency sound generation sources by interfering the frequencies of the low sounds from devices equally and in reverse phase relation. CONSTITUTION:When a low frequency composite sound to be attenuated is supplied to a controller 6 through a microphone 3, an amplifier 4 and a filter circuit 5, the controller 6 controls so that the sound level of the low frequency composite sound becomes minimum. In other words, the frequencies of two vibration conveyors 2a, 2b are equalized and set to reverse phase relation to interfere the low frequency sounds generated from the conveyors 2a, 2b, and th degree of acceleration or deceleration is calculated by a controller 6 with respect to the rotary machine 1a of the conveyor 2a to minimize the sound pressure level of the low frequency composite sound.

Description

DETAILED DESCRIPTION OF THE INVENTION a. Field of Industrial Application The present invention relates to a method for muffling low-frequency sounds generated from a plurality of rotating machines or a device having rotating machines.

b. Prior Art In petrochemical factories, machine shops, etc., when operating rotating machines or equipment with rotating machines, such as blowers, vibrating conveyors, compressor pumps, etc., low frequency sounds of 500 Hz or less are generated. The wavelength of this low-frequency sound is extremely long (about 340 m at IHz, about 17 m at 2011z).
Therefore, it is difficult to effectively attenuate low-frequency sounds even if the propagation path is shielded by an obstacle or the device is surrounded by a structure with a large transmission loss. In general, in the propagation of low frequency sounds, as seen in the propagation of audible sounds,
Absorption by air.

Because we cannot expect so-called excess attenuation other than geometrical distance attenuation, such as absorption due to ground surface conditions or diffraction due to walls, buildings, etc., it will propagate to unexpectedly long distances.

For this reason, in the past, the reality is that no countermeasures have been taken against low frequency sounds.

Problems to be solved by the C1 invention As a result, glass doors in private houses rattled, causing unexpected psychological damage, and contributing to noise pollution and vibration pollution.

Note that the propagation path of low-frequency sound generated from multiple rotating machines or equipment with rotating machines is complex, so
Conventional mufflers, such as resonance mufflers, could not be applied.

Means for Solving the d0 Problem The present inventors discovered that when devices having two rotating machines with similar frequencies are placed adjacent to each other, a beat phenomenon occurs as shown in FIG. We focused on the fact that the low-frequency synthesized sound pressure level in the trough of the beat is significantly lower than the low-frequency sound pressure level emitted from each device individually, and after considering various measures to take advantage of this phenomenon, we developed this book. This led to the completion of the invention.

In other words, the present inventors have found that by controlling the frequencies or rotational speeds of two sets of devices, each having a rotating machine, so that they are equal to each other and their phases are in an antiphase relationship, the low frequencies emitted from each device can be reduced. We found that wave sounds interfere with each other, and as a result, the synthesized sound pressure level of low-frequency sounds is greatly attenuated.

The present invention is characterized by a method for silencing low-frequency sounds generated from a plurality of rotating machines or a device having rotating machines. A synthesized sound of wave sound is detected, an optimum rotation speed of one set of the rotating machines is calculated so that the sound pressure level of the synthesized sound is minimized, and the rotation speed of the rotating machines is controlled based on the calculation output. A low-frequency sound silencing control method characterized in that the frequencies of the low-frequency sounds generated from the two sets of rotating machines or devices having rotating machines are set to be equal and have opposite phases to each other so that they interfere with each other. It is in.

e. Embodiment FIG. 1 is a basic configuration diagram showing an example of the low-frequency sound silencing control method according to the present invention, in which low-frequency sound emitted from vibrating conveyors 2a and 2b having rotating machines 1a and lb, respectively, is suppressed. It shows how to achieve effective attenuation.

The above-mentioned two vibrating conveyors 2a and 2b are arranged in series with each other, and a synthesized sound of low frequency sounds generated from the vibrating conveyors 2a and 2b, respectively, is detected at an approximately intermediate position between these vibrating conveyors 2a and 2b. Place microphone 3 in the optimal position. Then, the output signal of this microphone 3 is amplified by an amplifier 4 and sequentially supplied to a filter circuit 5 and a controller 6.

Note that the amplifier 4 is usually used for
l) Use a meter or sound level meter, etc. The filter circuit 5 is a 1/3 octave band filter or a 1 octave band filter for passing only the frequency to be attenuated.

Alternatively, it may be a 178 octave band filter or the like. Further, the controller 6 may be either an analog type or a digital type, but preferably a digital type controller, such as a microcomputer or a personal computer, whose control algorithm can be easily developed and changed is advantageous. It is.

However, microphone 3. When the low frequency synthesized sound to be attenuated is supplied to the controller 6 via the amplifier 4 and the filter circuit 5, the controller 6 performs control so that the sound pressure level of this low frequency synthesized sound is minimized. It will be done. In other words, the vibration frequencies of the two vibrating conveyors 2a and 2b are made equal,
In addition, the individual vibrating conveyors 2a are set in an anti-phase relationship.

In order to make the low-frequency sounds generated from the vibrating conveyors 2b interfere with each other and thereby minimize the sound pressure level of the low-frequency synthesized sound, the controller 6 controls the degree of speed increase or deceleration of the rotating machine 1a of one of the vibrating conveyors 2a. calculate.

The control means in the controller 6 will be described below.

When two vibrating conveyors 2a and 2b with similar frequencies are placed adjacent to each other, a beat phenomenon occurs, and the combined sound is expressed as follows.

The low frequency sounds of the vibrating conveyors 2a and 2b are each A+.

If At, then A 1 = P'+5in(2πf + j+θI)A
2=Pzsin(2yr fzt+θ2). However, P+, P2: Sound pressure f of vibration conveyors 2a, 2b
,, f2: Sound frequency of vibration conveyors 2a and 2b is 0
1, θ2: If the initial phase angle synthesized sound of the sounds of the vibrating conveyors 2a and 2b is A, then A=A, +A2=P, 5in (2tt f t+θ,)
+ P zsin (2πf2+θt), and f, = f, +Δf Δ(<f, (frequency is close), A=P+5in(2TCf r t+θ,) + P z
sin (2πf, t+(2πΔft+θ2)). Further calculation of the above formula results in A=Psin(2πf, t+θ). Here, P, cosθ, + P, 5in(2πΔft102
).

Note that Δf is the beat frequency, and 1/Δf is the beat period.

Further, the composite sound pressure level L of beat is expressed as follows.

Pa Note that Pa is the reference value of the sound pressure shown by the definition formula of the sound pressure level, and is the effective value of the minimum audible sound pressure, 2 Xl0-5 Pa (Pascal). In other words, to make the frequencies equal and the phases anti-phase, Δf is set to zero,
At the same time as eliminating the beat, the phase difference (2πΔft + θ2−
θI) is set to π, and the synthesized sound pressure level L is made the lowest.

f, , f2 change slightly due to changes in load, which causes beat, but in this embodiment, the beat phenomenon is suppressed by controlling the rotation speed. In this case, the controllable parameter is Δf, and the control width (the size of Δf) and the control time for shifting the phase by Δf (for example, Δf = f (t)) are determined by a predetermined algorithm.

The calculation output signal from this controller 6 is supplied to a rotation speed controller 7 generally called VVVF, and is sent to the vibration conveyor 2a.
The number of rotations of the rotation ala and the frequency of the vibration conveyor 2a are controlled. In this case, as an example of the control algorithm, since the low-frequency synthesized sound is usually in a beat state, a predetermined threshold value that becomes the synthesized sound pressure level L is set, and the synthesized sound pressure level L exceeds that threshold value. If the threshold value is exceeded, a speed increase or deceleration signal is issued, and the rotation of the rotating machine 1a is corrected until the resultant sound pressure level L becomes equal to or less than the threshold value.

The experimental results when using the above-mentioned silencing control method are shown in the second section.
As shown in the figure. In the case of Figure 2, the threshold value is 90 decibels (
dB), and as is clear from comparing the operation results before and after the start of control, the synthetic sound pressure level L can be controlled to 95 decibels (dB) or less at worst. can.

Although one embodiment of the present invention has been described above, the present invention is not limited to the embodiment described above, and various modifications and changes can be made based on the technical idea of the present invention.

For example, the vibrating conveyors 2a and 2b may be arranged in parallel, and the present method can also be applied to muffling devices other than the vibrating conveyors, such as devices that generate low frequency sounds such as blowers, compressor pumps, etc. be able to. Further, even when there are not two sources of low frequency sound but more than two, it is possible to divide them into two arbitrary groups and apply the present method.

f6 Effects of the Invention As described above, the present invention controls the rotational speed of two sets of rotating machines or rotating machines so that the frequencies of low-frequency sounds from each device are made equal and in opposite phase relation to each other so that they interfere with each other. Therefore, the low frequency sounds from the two sets of low frequency sound sources can be effectively muffled, which can be useful for preventing low frequency sound pollution. Furthermore, in order to prevent noise from each rotating machine or a device having a rotating machine, it has conventionally been necessary to install a resonance type muffling device or the like for each rotary machine, but according to the method of the present invention, a special muffling device can be installed. A common silencing circuit system can be used in common without the need to provide separate circuits, which is also advantageous in terms of economy.

[Brief explanation of drawings]

Fig. 1 is a basic configuration diagram showing an example of the low frequency sound silencing method according to the present invention, Fig. 2 is a graph showing the sound pressure level of low frequency sound before and after using the method of the present invention, and Fig. 3 is a vibration Sound pressure level of low-frequency sound emitted independently from each device when two devices with similar numbers are placed adjacent to each other
3 is a graph showing the synthesized sound pressure level of low frequency noise from various devices. Ia, lb...rotating machine, 2a, 2b...
Vibration converter, 3...Microphone, 4...Amplifier, 5...Filter circuit, 6...Controller,
7... Rotation speed controller.

Claims (1)

[Claims] A method for silencing low-frequency sounds generated from a plurality of rotating machines or a device having rotating machines detects a synthesized sound of low-frequency sounds generated from any two sets of rotating machines or devices having rotating machines, and Calculate the optimum rotation speed of one set of the rotating machines at which the sound pressure level of the synthesized sound is minimized, control the rotation speed of the rotating machines based on the calculation output, and control the rotation speed of the two sets of rotating machines or 1. A low-frequency sound silencing control method, characterized in that the frequencies of low-frequency sounds generated from devices each having a rotating machine are set to be equal and have opposite phases so that they interfere with each other.