JPS6279321A - Method for testing acoustic characteristics - Google Patents

Abstract

PURPOSE:To measure the acoustic characteristics of a material without requiring a special apparatus, by respectively inputting the interference sound of the direct sound from a sound source and the reflected sound from a material to be measured, and the direct sound in a free sound field to calculate the difference between sound pressure levels. CONSTITUTION:A sound source 2 generating random noise and the microphone 3 spaced apart from said sound source 2 by a distance D are arranged and the interference spectrum pattern of the direct sound of said sound source 2 and the sound once reflected from a material 1 to be measured is inputted to a frequency analyser 4. In the same way, the direct sound in a free sound field generating no reflection of sound is inputted to the analyser 4 and the difference between two frequency levels is calculated for each frequency. By this method, the distance attenuation of the sound between the sound source 2 and the microphone 3 and air absorbing attenuation are off set and only the effect of the material 1 to be measured can be observed. Therefore, the acoustic characteristics of the material can be measured without requiring a special apparatus.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is for selecting materials that can simulate the acoustic characteristics of the real thing in acoustic scale model experiments.

The present invention relates to a method for measuring the acoustic properties of materials, and can be applied to, for example, interior materials for rooms where acoustic properties are important.

[Conventional technology]

As shown in Figure 2, the conventional technology uses a sound source (horn driver unit a) in which a pipe is attached to a speaker and can generate spherical waves from the tip of the pipe, and a pure tone is generated by an oscillator to adjust the frequency of the oscillator. Measurements are made while changing the In order to obtain a constant sound output across all frequencies, a microphone length is attached to the sound source and a feed bank is sent to the excavator to adjust the output. Finally, the measured sound pressure level is recorded on a level recorder with frequency plotted on the horizontal axis, and compared with theoretically calculated values.

However, although the conventional method is for measuring the actual ground surface and is not for measuring the acoustic characteristics of a material like the present invention, the principle of measurement is the same. (<References> Takehiro Ikiyo et al. "Study on noise attenuation design of sound insulation walls taking into account the influence of the ground surface" Pollution Resource Research Institute Report No. 17 P45-P54 October 1980) Experiments due to different objects The frequency range of conventional technology is 10KHz
For the following, the present invention is from 0 to 100 KHz.

[Problem that the invention seeks to solve]

The conventional technology has the disadvantage that the following two operations require a large number of measuring devices, which makes the measuring device complicated and takes a long time.

(1) It is necessary to experiment with a constant acoustic output at each frequency, so the oscillator output is adjusted by feeding back the generated sound.

(It is necessary to experiment with pure tones, and in order to draw a spectral pattern over a wide range of frequencies, a device that gradually changes the frequency of the pure tone is required, and the time required to change it is also necessary for measurement.)

The present invention aims to solve the above problems.

[Means for solving problems]

In the present invention, a sound source 2 that generates random noise and a microphone 3 installed at a certain distance are placed on the material to be measured 1, and the direct sound from the sound source 2 and the microphone 3 are placed on the material to be measured 1 once. A first step of measuring the interference spectrum pattern with the reflected sound using the frequency analyzer 4 connected to the microphone 3 (measurement is performed in a sound field where there is no reflected sound other than the sound reflected by the material to be measured 1); The relative positions of the sound source 2 and the microphone 3 remain unchanged, and the sound source 2 and the microphone 3 are placed in a sound field without sound reflection (free sound field), and the direct sound from the sound source 2 is transmitted at the frequency specified above. A second step of similarly measuring using the analyzer 4, and a third step of obtaining a spectrum pattern by subtracting the sound pressure level measured in the second step from the sound pressure level measured in the first step for each frequency. With Preparation 9 and above, the sound attenuation due to the distance between the sound source 2 and the microphone 3 and the sound attenuation due to the absorption of air molecules are canceled out, and a spectral pattern due only to the influence of the material to be measured 1 is obtained, which can be used as the theoretical calculation value. The method is characterized in that the acoustic characteristics of the material to be measured 1 are measured in the fourth step of comparison.

Note that the spectrum pattern is a graph in which the experimental frequency is plotted on the horizontal axis and the measured sound pressure level is plotted on the vertical axis.

[Effect]

The present invention does not require any special equipment other than the use of a nine-frequency analyzer, as long as the sound source can generate random noise. As shown in Figure 1, two problems can be solved by performing free-field measurements and calculating the difference in sound pressure level between measurement 1 (first step) and measurement 2 (second step). will solve everything.

Advantages include (1) experimenting with random noise;
There is no need to change the frequency. (2) The frequency characteristics of the sound source do not matter as long as the frequency is equal to or higher than the required level (cancelled by a subtraction operation).

〔Example〕

Next, one embodiment of the method of the present invention will be explained based on the drawings.

In FIG. 1, a sound source 2 is placed at a point A on a material to be measured 1, a microphone 3 is placed at a distance from the point A,
The sound received by the microphone 3 is input to the frequency analyzer 4 and analyzed (measurement 1).

The content of the analysis is a spectrum pattern of the sound pressure level in the experimental frequency range, and the spectrum pattern 7 is a graph in which the horizontal axis represents the experimental frequency and the vertical axis represents the sound pressure level.

This measurement is carried out in an anechoic chamber so that reflected sound other than the sound reflected by the material to be measured 1 does not act.

Next, perform the same measurement and analysis in the same anechoic chamber, leaving the positional relationship between the sound source 2 and the microphone 3 unchanged (Measurement 2
). By subtracting the analysis result of measurement 1 from the analysis result of measurement 1 with the frequency analyzer 4 (which can perform spectrum subtraction internally), the sound source 2. The distance attenuation of the sound between the microphones 3 and the air absorption attenuation cancel each other out, and only the influence of the material to be measured 1 can be seen.

Subtracting the analysis results means subtracting the sound pressure level for each measurement frequency.2For example, it can be considered as follows. The analysis result of measurement 1 shows that if we focus on a certain frequency, the distance attenuation and air absorption attenuation can be subtracted from the sound pressure level after the sound generated from sound source 2 is affected by the material to be measured 1. sound pressure levels have been observed.

- In force measurement 2, the sound pressure level obtained by subtracting distance attenuation and air absorption attenuation from the sound generated from sound source 2 at the frequency of interest is observed. Therefore, as shown in FIG. 3, only the influence of the material to be measured 1 can be seen.

A method for determining acoustic impedance as one of the acoustic characteristics of a material from the measurement and analysis results will be described below in accordance with the flowchart of FIG. The method is the same as the conventional technique. First, we theoretically calculate the spectral pattern due to the influence of the material by giving the acoustic impedance of the material, and then compare it with the spectral pattern due to the influence of the material under test, which was measured and analyzed experimentally.The acoustic impedance of the material is changed until it matches, and then This method uses the acoustic impedance of the material used in the calculation as the acoustic impedance of the material to be measured.

〔Effect of the invention〕

As described above, according to the present invention, the acoustic characteristics of a material (in this case, a spectral pattern representing the influence of the material) can be measured without the need for special equipment as in the prior art.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing one embodiment of the method of the present invention. FIG. 2 is an explanatory diagram showing a conventional experimental apparatus for measuring excessive attenuation of sound propagating from a point sound source due to the ground surface, and FIG. 3 is an explanatory diagram showing the meaning of the subtraction operation. FIG. 4 is a flowchart for determining the acoustic impedance of a material. 1... Material to be measured, 2... Sound source, 3... Microphone, 4
...Frequency analyzer. @2 edict

Claims (1)

[Claims] A sound source 2 that generates random noise and a microphone 3 placed a certain distance apart are placed on the material to be measured 1, and the direct sound from the same sound source 2 and the sound reflected once on the material to be measured 1 are measured. The first step is to measure the interference spectrum pattern of the same sound source 2 and the same microphone 3 using the frequency analyzer 4 connected to the same sound source 2 and the same microphone 3, while leaving the relative positions of the same sound source 2 and the same microphone 3 unchanged. A second step in which the frequency analyzer 4 is installed in a sound field without sound reflection (free sound field) and the direct sound from the same sound source 2 is similarly measured using the frequency analyzer 4, and a first step in which each frequency is measured. a third step of obtaining a spectrum pattern by subtracting the sound pressure level measured in the second step from the sound pressure level measured;
An acoustic property testing method comprising a fourth step of comparing the spectrum pattern obtained in the third step with a theoretically calculated value.