JPH03289521A - Method and apparatus for reducing sound emitted from vibrating body - Google Patents

Abstract

PURPOSE:To ensure the effective decrease in noises by measuring the vibration and the sound of a vibrating body, analyzing the frequencies in real time, comparing the characteristic frequencies of the vibration and the sound, and clarifying the causal relation and the correlation between the vibration and the sound. CONSTITUTION:A vibration sensor 5 is fixed to a vibrating body 3 and measures the vibration. The vibration is amplified in a charge amplifier 9. A noise meter 7 measures the sound of the vibrating body 3. A high-speed Fourier transformation device 11 performs the Fourier transformation of the vibration output of the amplifier 9 and the sound output of the noise meter 7 at a high speed, analyzes the frequencies in real time and outputs the results into a personal computer 13. The computer 13 computes the theoretical frequency in each mode of the vibrating body 3. The results of the computations are compared with the result of the analysis in the device 11. It is judged that the noises can be reduced by decreasing which frequency component of the vibrations. Thus, the causal relation and the correlation between the vibration and the noises can be clarified, and the noises can be positively decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a method and apparatus for efficiently reducing sound generated from a vibrating body.

(Prior Art) Generally, it is well known that when an object vibrates, the vibrating surface vibrates air molecules in the vicinity and generates sound.

(Problem to be Solved by the Invention) By the way, regarding the causal relationship and correlation between the vibration of this vibrating body and the sound generated from this vibrating body,
had not been fully elucidated.

Therefore, the current situation is that no effective means have been considered for how to efficiently reduce the sound generated from vibrating bodies. was an important issue.

An object of the present invention is to solve the above-mentioned problems by elucidating the causal relationship and correlation between vibrations and the sound generated from the vibrations, so that the noise radiated from a vibrating body can be reliably and efficiently reduced. An object of the present invention is to provide a method and device for reducing sound.

[Configuration of the Invention (Means for Solving the Problem) In order to achieve the above object, the present invention measures the vibration of a vibrating body, measures the sound radiated from the vibrating body, and compares the vibration and the sound. A vibration characterized by performing real-time frequency analysis on the vibration, comparing characteristic frequencies of the vibration and sound, and determining whether noise can be reduced by reducing which frequency component of the vibration. This is a method of reducing the sound emitted from the body.

The present invention also provides a vibration sensor that measures the vibration of a vibrating body, a sound level meter that measures the sound emitted from the vibrating body, a fast Fourier transformer that performs real-time frequency analysis of the vibration and sound, and a fast Fourier transformer that performs real-time frequency analysis of the vibration and sound. A calculation device that compares characteristic frequencies of vibration and sound and determines whether noise can be reduced by reducing which frequency component of the vibration, and a plotter that outputs necessary information of the calculation device. This is a device for reducing sound emitted from a vibrating body.

(Function) By adopting the method for reducing sound emitted from a vibrating body of the present invention, the vibration of the vibrating body is measured, the sound emitted from the vibrating body is measured, and the vibration and sound are measured in real time. Perform frequency analysis and compare the respective characteristic frequencies of the vibration and sound,
It is determined whether noise can be reduced by reducing which frequency component of the vibration, and the causal relationship and correlation between vibration and the sound generated from vibration are clarified, and noise is reliably and efficiently reduced. be done.

Further, the device for reducing sound emitted from the vibrating body of the present invention includes:
The vibration of the vibrating body is measured with a vibration sensor, the sound emitted from the vibrating body is measured with a sound level meter, the vibration and sound are subjected to real-time frequency analysis with a fast Fourier transform device, and the vibration and sound are each A plotter is provided which compares the characteristic frequencies of and determines whether noise can be reduced by a calculation device depending on which frequency component of the vibration is to be reduced, and outputs necessary information of the calculation device.

(Example) Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 shows a block diagram of an embodiment of the sound reduction device of the present invention. The sound reduction device 1 mainly includes a vibration sensor 5, a sound level meter 7, a charge amplifier 9, and a fast Fourier transform device 1.
1, an arithmetic unit, in this embodiment a personal computer (personal computer) 13, and a plotter 15.

The vibration sensor 5 is fixed to a vibrating body, for example, the iron plate 3, and measures vibrations of the iron plate 3. A sound level meter 7 measures the sound generated from the iron plate 3, and a charge amplifier 9 amplifies the output of the vibration sensor 5. Note that 17 is a spring, and F is an excitation direction that gives vibration to the iron plate 3.

Further, the fast Fourier transform device 11 includes a charge amplifier 9
The vibration output amplified by the sound level meter 7 and the sound output of the sound level meter 7 are subjected to high-speed Fourier transform, subjected to real-time frequency analysis, and outputted to the personal computer 13.

The personal computer 13 has built-in software that calculates the theoretical frequency according to each mode of the vibrating body 3, and calculates the theoretical frequency and the fast Fourier transform device 11.
The results of real-time frequency analysis are compared to determine which frequency components of vibration should be reduced to effectively reduce noise. The plotter 15 inputs these calculation results and outputs necessary information for the personal computer 13.

FIG. 2 is a comparison diagram of real-time frequency analysis results of vibration and noise using a fast Fourier transform device. Comparing the vibration caused by the fast Fourier transform device 11 and the noise caused by this vibration, the sound is strongly generated at frequencies fo and f3, which are odd modes, but at frequencies f1, which is an even mode.
f2. At f4, no sound is generated due to cancellation.

FIG. 3 shows the calculation results of the theoretical frequencies in each mode of the vibrating body by a personal computer.

FIG. 4 shows an example of the even mode shown in FIG. 2, and FIG. 5 shows an example of the odd mode. There are two types of vibration modes: even mode and odd mode. even mode (2,1),
In (2, 2) and (3, 2), the vibration node where the amount of displacement is zero is located at the center of the vibrating body 3, so the number of vibration crests and troughs is the same.

That is, the effects of sound radiation (peaks of vibration) and sound absorption (number of troughs) are the same, and no sound is radiated from the vibrating body 3. This is called cancellation in even mode. On the other hand, odd modes (1, 1), (3
, 1), the number of vibration crests and troughs do not match, so sound is radiated from the vibrating body 3.

Therefore, the personal computer 13 searches for the odd mode vibration frequency and investigates the loudness of the sound at that frequency. That is, by finding the vibration frequencies in the odd mode that are producing a large amount of sound, and reducing the vibrations in the order of the vibration frequencies of the vibrating body 3 that are producing a large amount of sound, the frequency fO is reduced as shown in FIG. and f3 to lower this sound, or this frequency fO
, f3 are made small or large, the sound can be heard quietly to large ears, and the sound generated from the vibrating body 3 can be effectively reduced.

Next, FIG. 6 shows a flowchart of the sound reduction device in FIG. 1. In the figure, the vibration and sound of the vibrating body 3 are subjected to real-time frequency analysis using the fast Fourier transform device 11 (step S1), and the analysis results are input into the personal computer 13 (step 2). At this time, the personal computer 13 calculates the theoretical frequency in each mode of the vibrating body 3 (step 3).

If the characteristic frequency obtained by real-time frequency analysis of the vibration using the personal computer 13 and the theoretical frequency in each mode roughly match (step 4), the frequency at which the vibration is increasing and the frequency at which the sound is increasing are determined. Step 5) Consider ways to reduce the vibrations in the odd modes where the sound is strongly generated, such as the stiffness of the sound source and Change the mass (step 6).

Note that if the characteristic frequency in (Step 4) and the theoretical frequency do not match, the experimental method and theoretical analysis are reconsidered (Step 7). The characteristic frequency of vibration in the above refers to the natural frequency.

In this way, the frequency of the vibration body 3 in the odd mode is
Accurate results can be obtained by comparing experiments and theoretical analysis, making it possible to efficiently reduce sound.

In addition, by adopting theoretical methods for reducing sound from the vibrating body, it has become possible to consider efficient low-pitched sound reduction at the design or prototyping stage.

It should be noted that the present invention is not limited to the above-mentioned embodiments, and may include appropriate design changes, for example, in order to extract the characteristic frequency of the vibrating body 3, instead of real-time frequency analysis, a transfer function is determined and this transfer function is The feature frequency may be extracted using a function.

[Effects of the Invention] As already clear from the above description, the method and device for reducing sound emitted from a vibrating body of the present invention measure the vibration of the vibrating body, and measure the sound emitted from the vibrating body. The problems of the prior art are effectively solved by performing real-time frequency analysis of the vibration and sound, comparing the respective characteristic frequencies of the vibration and sound, and reducing which frequency component of the vibration. As a result, the causal relationship and correlation between vibration and the sound generated from vibration are clarified, making it possible to consider reliable and efficient noise reduction at the design, planning, or prototyping stage.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the sound reduction device of the present invention;
Figure 2 is a comparison diagram of the real-time frequency analysis results of vibration and noise using a fast Fourier transform device, Figure 3 is the result of calculation of the theoretical frequency in each mode of the vibrating body by a personal computer, and Figure 4 is the same as Figure 2. Example of even mode shown, fifth
The figure shows an example of the odd number mode, and FIG. 6 is a flow sheet of the sound reduction device in FIG. 1. 1... Sound reduction device 3... Vibrating body 5... Vibration sensor 7... Sound level meter 9... Charge amplifier... Fast Fourier transform device 3... Personal computer 5... Plotter controller Man

Claims (2)

[Claims] (1) Measuring the vibration of a vibrating body, measuring the sound emitted from the vibrating body, performing real-time frequency analysis of the vibration and sound, and comparing the respective characteristic frequencies of the vibration and sound, A method for reducing sound emitted from a vibrating body, comprising determining whether noise can be reduced depending on which frequency component of the vibration is to be reduced. (2) a vibration sensor that measures the vibration of a vibrating body; a sound level meter that measures the sound emitted from the vibrating body; a fast Fourier transform device that performs real-time frequency analysis of the vibration and sound; and a plotter that outputs necessary information of the arithmetic device; A device for reducing sound emitted from a vibrating body, characterized by: