JPS6184526A - Measuring device for acoustic transmission loss of material - Google Patents

Abstract

PURPOSE:To take a measurement with a small sample and speedily without requiring any special reverberation chamber, etc., by connecting two acoustic pipes which have the same sectional shape to each other across the sample, and fitting a speaker to one end part and a sound absorber to the other end part. CONSTITUTION:The speaker 2 is fitted to an end part of one of acoustic pipes 1 and 1 which have the same sectional shape, and microphones 4 are inserted at >=2 specific positions. The sound absorber 3 is inserted into an end part of the other acoustic pipe and a microphone 4 is inserted at >=1 specific position. Those acoustic pipes 1 and 1 are connected together by connectors 5 which are arranged at the other-terminal sides of both acoustic pipes 1 along the outer peripheries of the pipes, have a small spring constant, and connect the acoustic pipes to both sides of the sample 6 without radiating a sound in the acoustic pipe to the outside. Then, signals of the microphones are processed on Fourier transform basis at the same time and data on them are processed by calculation.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for quickly and conveniently measuring the sound insulation properties of materials.

Modern life is carried out in the presence of a variety of noises such as neighborhood noise, traffic noise, and factory noise.In order to ensure a comfortable living space, protect privacy, and noise issues, it is important to use sound insulation materials that have excellent sound insulation properties. And yes! 7. Materials that are thin and light are required. This means that it is necessary to improve sound insulation not only by the mass of the material, as has been the case up until now, but also by internal absorption.

Conventionally, when developing sound insulating materials, their performance was generally evaluated by a method using a reverberation chamber as specified in 1, T Engineering SA A1416, etc. However, since this method is aimed at measuring in a form close to the actual wall structure, it has the following difficulties from the perspective of material development.

(1) Measurement results do not necessarily represent the material properties due to the influence of the sample area, shape, mounting method, etc.

(2) Since a large-area sample is required, it is not possible to easily re-manipulate prototype production and measurements.

(3) Measurement facilities and equipment are expensive.

(4) It takes time and money to measure - times.

The present invention was made in view of the above-mentioned circumstances, and it is an object of the present invention to provide a device that can quickly measure the sound insulation properties of a material itself using a small sample without requiring a special reverberation chamber or anechoic chamber. The purpose is to

Hereinafter, the present invention will be described in detail with reference to the drawings.

Normal incidence sound transmission loss (TL), which represents the sound insulation properties of a material
When considering 1, we make three theoretical first-order assumptions. That is, in FIG. 1, \Assumption 1 Both the incident wave and the transmitted wave are plane waves that propagate perpendicularly to the material surface.

Assumption 2: The material is a flat plate with an infinite area.

Assumption 3: The transmitted wave does not reflect to infinity.

Based on these assumptions, the theoretical formula for TL derived assuming that there is no absorption inside material A is known as the "mass front"1. Give TL.

In other words, the above three assumptions can be experimentally approximated as 1 and the incident sound pressure Pi and transmitted sound pressure pt can be separated from the reflected wave and 6111
If it can be determined, TL can be measured as a material property regardless of the presence or absence of internal absorption, and the degree of internal absorption of the material can be evaluated by comparing the mass with the previous mass. In the past, it was not possible to measure TL as a material property (because it was difficult to achieve these conditions).

Embodiments of the invention are shown in FIGS. 2 to 5.

Regarding assumptions 1 and 3 among the above assumptions, respectively,
It is known that this can be achieved by using an acoustic tube (1) and by inserting a sound absorbing material (3) at the end of the transmission side acoustic tube to make it a non-reflective end.

However, even when the sample (6) is directly attached to this, the measured TL shows a much larger value than the original value of the material, and the error becomes larger especially as the number of vibrations decreases. Therefore, we conducted a study based on numerous experiments, including changing the type and mounting method of the sample.A: For example, a sample made of thin rubber and having the shape shown in Figure 3 has a small spring constant.
A new plate shows that if a sample with the same shape as the cross-section of the acoustic tube is connected to the acoustic tube (via a connector (5) that prevents the sound inside the tube from leaking out), a state that satisfies assumption 1 and 2 can be created. In the case of vertical incidence, the sample surface moves in translation due to the uniformly applied sound pressure Vζ, whereas when the sample is directly attached to the sound tube, the periphery of the sample is restrained, causing oily stress inside the sample.) It is considered that as a result of the movement of the sample being suppressed by the stiffness of the sample, TL is measured to be larger than the original value. When the sample and acoustic tube are connected using the connector shown in Figure 3, due to its low spring constant, almost no reaction force is generated against the movement of the sample due to sound pressure, and the force is approximately infinite. It is possible to create a similar state by cutting out part of a flat plate.

Basically, the above method is sufficient, but since it is impossible to make the spring constant of the connector exactly zero, if the rigidity of one sample is small and the spring constant of the connector cannot be relatively ignored, one sample Disturbances may occur in the measured TL curve due to the influence of natural vibration modes fixed around the periphery. Regarding this problem, as shown in Figure 4, it is necessary to attach a metal fitting (
Problem 7) could be resolved by attaching the fixing device (8). In other words, one sample is supported by (5) and (8), and the supporting force is more evenly distributed over the entire sample surface than when supported by only one (5). The following natural vibration modes are suppressed, making it possible to measure even samples with low rigidity.

As mentioned above, the measurement method of the present invention assumes plane waves, but there is an upper limit to the frequency range of 1,000 plane waves even if an acoustic tube is used.) This depends on the shape and size of the acoustic tube cross section. It's decided. In general, if the size is made smaller, plane waves can be maintained up to high frequencies, but on the other hand, the area of the sample must also be made smaller). Spring constant and sample (
6) The resonance point caused by the mass becomes higher. Therefore, the measurable frequency range is from near the resonance point and above to the plane wave region, and if the size of the sound tube cross section is increased, the upper limit of the measurable frequency range will be lower, and if the size is smaller, the lower limit will be higher. There was a contradiction. Therefore, in order to solve this contradiction and expand the measurement area, for example, as shown in Figure 5, a steel plate with a thickness of 0.35 mm was used inside one acoustic tube to provide partitions parallel to the direction of propagation of the sound waves. . As a result, the acoustic tube can be regarded as an assembly of acoustic tubes with a diameter smaller than 1, and only the upper limit frequency can be increased without increasing the resonant frequency.

The measurement procedure is as follows.

(1) The signal generated by the noise generator is transmitted to the speaker (2)
) and use this as the sound source.

(2) Simultaneously perform Fourier transform on the signals from microphones $1 and $2 to measure a transfer function.

(3) Similarly, microphone keys 1 and f-3 or $1
Measure the transfer functions of 3 and -11-4, respectively.

(4) Calculate TL from the measured transfer function by numerical calculation using a computer or the like.

As already mentioned, there are traveling waves and backward traveling waves in the acoustic tube, and it is necessary to separate them in order to calculate NTL. The method is clear in principle, and the method described below can be used.

Figure 6 shows Oite, U, , VI, US, and Vt, respectively.
Incident wave at the position of microphone 1 at a certain moment 1 Reflected wave at the position of microphone 2 1 Transmitted wave at the position of microphone 3) Reflected wave from the non-reflecting end at the position of microphone "7F4"A Both are in the frequency range The Fourier transform of the output of the microphone ≠ 1 to 4 is assumed to be the complex sound pressure spectrum of
4, the relationship between M to M4 and U,V,,V is expressed as follows.

M1=U, +V+exp(-j(1)d/c:]
(1) M, = V, +U, exp [knee jωd/c]
(2) M, = lJ2 + V2exp (jωd/c)
(3) M4=%+UteXpCJωd/C':l
(4) Here d is microphone key 1~41:2
and: distance from 3 to 4, C is the speed of sound, ω is the angular frequency, j
is an imaginary unit. Equations (1) and (2), and (3)
From formula and formula (4), %U1 and Vl
, Ut and V are separated into equal constraints. By definition, the sound transmission loss TL is as follows. Therefore, substituting the equation λ(5)/(7) into the equation (9) and transforming it gives 9, resulting in 13 types of transfer functions, Mt/ll+, M4/! 1
13. TL can be found from M3/Ml.

In addition, in the frequency range where the reflection from the heat input reflection end can be ignored, 1 M, == M, exp (-jωa/c) (1
t), TL is as follows.In this case, TL can be obtained by simply measuring two transfer functions, Ms/J and Mt/Mt.

Note that all microphone outputs may be measured simultaneously, or may be measured for each set whose transfer function is to be measured.

FIGS. 7 and 8 show a comparison of the actual measured values shown by a single solid line with the mass side shown by a broken line in a measurement example for a disk sample having a diameter of about 10 cm. Figure 7) is a steel plate (4.25 mm) that has almost no internal absorption and is said to follow the mass side well.
As is clear from the figure, the actual measured value and the mass almost match. Although Fig. 8 shows a gypsum board (9 mm thick) which is said to have good sound insulation properties, it shows a value that is 2 to 3 dB larger than its mass.

This shows that the gypsum board is porous, so internal absorption is high, so it actually has good sound insulation properties.

As described above, the present invention not only makes it possible to measure sound transmission loss as the sound insulation property of a material, but also makes it possible to evaluate the degree of internal absorption by comparing it with the mass side.

Furthermore, since this device can perform measurements much more quickly and easily than conventional measuring methods, it can be an effective means for research and development of sound insulation materials and product management. Furthermore, since the measurement results obtained by the device of the present invention directly represent the material properties, it can be expected that they can be used as basic data for more rational design of sound insulation structures.

Therefore, it is believed that the spread of the sound transmission loss measurement device for materials according to the present invention will promote the research and development of superior sound insulation materials, and in turn will greatly contribute to the improvement of livability in terms of sound insulation.

[Brief explanation of drawings]

Figure 1 is a conceptual diagram of normal incidence sound transmission loss. Figure 2 is a block diagram of the measuring device. Figure 3 is the connection device. Figure 4 is a perspective view of the sample connection part of the acoustic tube. Figure 5 is the internally partitioned acoustic tube. Figure 6 is a diagram of the positional relationship between microphones and sound waves. Figure 7 is an example of measuring a steel plate. Figure 8 is an example of measuring a plaster plate.

Claims (3)

[Claims] (1) For two sound tubes with the same cross-sectional shape, one end has a speaker attached so that microphones can be inserted at two or more predetermined positions, and the other sound tube has a sound absorbing material at one end. one that allows the microphone to be inserted into one or more predetermined positions, and one that has a small spring constant and that is placed along the outer periphery of the tube at the other end of both acoustic tubes. A connecting device with a structure that allows an acoustic tube to be connected to both sides of a sample without leaking sound, two to four microphones, a device that can simultaneously perform Fourier transformation of signals from two to four microphones, and a Fourier transformer. A sound transmission loss measurement device for materials, which includes a device that calculates converted data and a device that generates noise that is input to a speaker. (2) Fix a highly rigid plate, cylindrical lattice, or a combination of these to the sample connection surface of the sound tube so that the projected area to the sample surface is the smallest, and attach a small spring constant to the sample side. An apparatus for measuring sound transmission loss of a material according to claim 1, which has a structure in which the supporting force against vibration of the sample is shared with the connector by attaching supports at one or several locations. (3) Inside the acoustic tube, install a partition plate that is highly rigid, thin, plate-shaped, cylindrical, or a combination of all or part of these, so that the cross-sections of the acoustic tube perpendicular to the direction of sound wave propagation are equal. An apparatus for measuring sound transmission loss of a material according to claim 1 or 2, which has a structure partitioned into two.