JP7690167B2 - Sound absorbing material - Google Patents

Description

The present invention relates to sound-absorbing materials.

Various types of sound-absorbing materials and structures have been proposed so far. For example, as shown in Figure 1, a porous type sound-absorbing material made of a porous material such as urethane foam, as shown in Figure 2, a perforated plate type sound-absorbing material made of a plate with many holes, as shown in Figure 2, and an air layer type sound-absorbing structure in which an air layer is placed on the back side of a plate as shown in Figure 3 are known (see, for example, Patent Documents 1 to 3). These sound-absorbing materials and structures are used in vehicles, buildings, road facilities, etc.

JP 2004-037582 A JP 2018-141839 A JP 2005-283703 A

However, as shown in the graph on the right side of Figure 1, porous sound-absorbing materials have the drawback that while they can achieve a high sound absorption coefficient over a fairly wide range in the high frequency band, they have a low sound absorption coefficient in the low frequency band. However, even with this porous sound-absorbing material, the sound absorption coefficient in the low frequency band can be increased by increasing its thickness. In this case, however, the problem arises that it becomes difficult to adopt this sound-absorbing material in applications where thickness is limited.

In contrast, perforated plate type sound absorbing materials and air layer type sound absorbing structures can achieve a high sound absorption rate in the low frequency range, as shown in the graphs on the right side of Figures 2 and 3. However, perforated plate type sound absorbing materials and air layer type sound absorbing structures have the disadvantage that such high sound absorption rates can only be achieved near certain frequencies.

The present invention has been made to solve the above problems, and provides a sound-absorbing material that can provide excellent sound-absorbing effects over a wide frequency range, including low frequencies, while keeping the thickness of the sound-absorbing material small.

The above problem is solved by providing a sound-absorbing material that is characterized by having a non-breathable sound-insulating part arranged on at least one surface of the breathable sound-absorbing body, which diffracts sound waves incident on the sound-absorbing body.

This is because, whereas a typical sound-absorbing material (such as the porous sound-absorbing material described above) has a high sound absorption coefficient when its thickness is equal to 1/4 of the wavelength of the incident sound waves, the sound-absorbing material of the present invention has a non-breathable sound-insulating part arranged on the surface of the breathable sound-absorbing body, so that the sound waves incident on the sound-absorbing body are diffracted by the sound-insulating part. This lengthens the path length of the incident sound waves inside the sound-absorbing body (increases the apparent thickness of the sound-absorbing body), and shifts the frequency band where the sound absorption coefficient is high to the lower frequency side. This means that it is possible to absorb sound from low frequencies without making the sound-absorbing body thicker.

In the sound-absorbing material of the present invention, the sound-insulating part may be disposed on at least one surface of the sound-absorbing material body (the side where sound is incident), but it may also be disposed on both surfaces of the sound-absorbing material body (the side where sound is incident and the side where sound is transmitted). Hereinafter, the surface of the sound-absorbing material body on which the sound-insulating part is disposed (or the side on which the sound-insulating part is disposed) may be referred to as the "sound-insulating part disposition surface."

In the sound-absorbing material of the present invention, the sound-insulating portion only needs to be provided at least in one location on the surface of the sound-absorbing material body where the sound-insulating portion is arranged. In this way, even with one sound-insulating portion, the above-mentioned diffraction effect can be obtained, so that the frequency band where the sound absorption coefficient is high can be shifted to the lower frequency side. However, providing sound-insulating portions in multiple locations makes it easier to obtain a uniform sound-absorbing effect regardless of the location on the sound-absorbing material body. For this reason, it is preferable to provide the sound-insulating portion in multiple locations on the surface of the sound-absorbing material body where the sound-insulating portion is arranged. In this case, it is more preferable to repeatedly arrange multiple sound-insulating portions on the surface of the sound-insulating portion with a gap between them. The dimensions and shapes of the sound-insulating portions may be one or multiple types, or may be different for each sound-insulating portion.

In the sound-absorbing material of the present invention, the flow resistance (airflow resistance) of the sound-absorbing material body is lower than the flow resistance (airflow resistance) of the sound-insulating portion. The flow resistance of the sound-absorbing material body (meaning the flow resistance measured by the method specified in the International Organization for Standardization standard "ISO 9053" or the American Society for Testing and Materials standard "ASTM C522" (hereinafter the same)) is preferably 10 ⁷ N·s/m ⁴ or less. On the other hand, the flow resistance of the sound-insulating portion is preferably 10 ⁸ N·s/m ⁴ or more. If the flow resistance of the sound-absorbing material body is higher than the above value (10 ⁷ N·s/m ⁴ ), sound is likely to be reflected by the sound-absorbing material body, and the sound-absorbing performance of the sound-absorbing material may be reduced, and if the flow resistance of the sound-insulating portion is lower than the above value (10 ⁸ N·s/m ⁴ ), the sound-insulating performance of the sound-insulating portion may be reduced, and the above-mentioned diffraction may be difficult to occur.

In the sound-absorbing material of the present invention, the surface density of the sound-insulating part is not particularly limited. However, generally, a material with a low surface density has low sound-insulating properties. For this reason, if the surface density of the sound-insulating part is low, the above-mentioned effect (the effect of shifting the frequency band in which the sound absorption coefficient is high to the low frequency side) may be difficult to achieve. Therefore, it is preferable that the surface density of the sound-insulating part is 0.01 kg/ ^m2 or more. As described later, the sound-insulating part may or may not be integrated with the sound-absorbing material body, and when the sound-insulating part is not integrated with the sound-absorbing material body, it is more preferable that the surface density of the sound-insulating part is 0.1 kg/ ^m2 or more.

Here, "integrating the sound-insulating part with the sound-absorbing material body" means integrating the sound-insulating part with the sound-absorbing material body so that they vibrate as one unit. In contrast, "not integrating the sound-insulating part with the sound-absorbing material body" means providing the sound-insulating part and the sound-absorbing material body in a state where the sound-insulating part and the sound-absorbing material body do not vibrate as one unit, but rather vibrate independently (a state where they do not affect each other's vibrations by coming together and separating. Ideally, a state where it can be thought of as if there is a thin layer of air (an air layer of infinitesimal thickness) between the sound-insulating part and the sound-absorbing material body), regardless of whether the sound-insulating part is in close contact (contact) with the sound-absorbing material body or not.

In the sound-absorbing material of the present invention, the material forming the sound-absorbing body is not particularly limited as long as it has the desired breathability (sound absorption). Examples of materials forming the sound-absorbing body (materials having breathability) include porous materials. Examples of porous materials include foamed resins (open-cell type) such as urethane foam and polyethylene foam, and nonwoven fabrics such as chemical fiber felt and natural fiber felt. The concept of "nonwoven fabric" also includes glass wool and rock wool.

In the sound-absorbing material of the present invention, the material forming the sound-insulating portion is not particularly limited as long as it has the desired non-breathability (sound-insulating properties). The sound-insulating portion can be a patch-like member (including not only planar ones but also long, thin strip-like ones) attached to the surface of the sound-absorbing material body. The sound-insulating portion can also be formed by a paint-based material applied to the surface of the sound-absorbing material body. Furthermore, the sound-insulating portion can also be a molten film portion formed on the surface of the sound-absorbing material body.

In the sound-absorbing material of the present invention, the ratio of the sound-insulating parts to the sound-insulating part-arranged surface of the sound-absorbing material body is not particularly limited. However, if the ratio of the sound-insulating parts to be arranged is too small, the above-mentioned diffraction phenomenon may not easily occur. For this reason, it is preferable that the ratio _S2 / _S1 of the total area _S2 of the sound-insulating parts arranged on the sound-insulating part-arranged surface of the sound-absorbing material body to the area _S1 of the sound-insulating part-arranged surface of the sound-absorbing material body is 0.1 or more.

In the sound-absorbing material of the present invention, it is also preferable to cover the surface of the sound-insulating portion opposite the sound-absorbing material body with a breathable sound-absorbing covering material. This not only shifts the frequency band with a high sound absorption coefficient to the lower frequency side, but also improves the sound absorption coefficient in the high frequency band, making it possible to obtain a sound-absorbing effect over a wider frequency band. The sound-absorbing covering material can be made of the same material as the sound-absorbing material body described above. The sound-absorbing covering material may be thick (having a thickness similar to that of the sound-absorbing material body) or thin (membrane-like).

The sound-absorbing material of the present invention described above can also be stacked in the thickness direction to form a polymerized sound-absorbing material. This allows the frequency band with a high sound absorption rate to be shifted further to the lower frequency side, making it possible to obtain a sound-absorbing effect over a wider frequency band. In a polymerized sound-absorbing material, it is also preferable to arrange the sound-insulating portion of one layer of sound-absorbing material and the sound-insulating portion of another layer of sound-absorbing material arranged above the first layer so that they do not overlap in the thickness direction.

As described above, the present invention makes it possible to provide a sound-absorbing material that can provide excellent sound-absorbing effects over a wide frequency range, including low frequency ranges, while keeping the thickness of the sound-absorbing material small.

FIG. 1 is a diagram showing the appearance of a conventional porous sound-absorbing material and its sound-absorbing characteristics. 1 is a diagram showing the appearance of a conventional perforated plate-type sound absorbing material and its sound absorbing characteristics. FIG. 1 is a diagram showing the structure of a conventional air-layer type sound-absorbing material and its sound-absorbing characteristics. 1 is a perspective view showing the appearance of a sound-absorbing material according to a first embodiment; 1 is a cross-sectional view showing a state in which the sound-absorbing material of the first embodiment is cut along a cross section perpendicular to its surface. 1 is a photograph showing the appearance of a sound-absorbing material according to a first embodiment. FIG. 11 is a perspective view showing the appearance of a sound-absorbing material according to a second embodiment. FIG. 11 is a perspective view showing the appearance of a sound-absorbing material according to a third embodiment. FIG. 11 is a perspective view showing the appearance of a sound-absorbing material according to a fourth embodiment. FIG. 13 is a perspective view showing the appearance of a sound-absorbing material according to a fifth embodiment. FIG. 13 is a perspective view showing the appearance of a sound-absorbing material according to a sixth embodiment. FIG. 13 is a perspective view showing the appearance of a sound-absorbing material according to a seventh embodiment. A cross-sectional view showing the appearance of a sound-absorbing material of the eighth embodiment. A cross-sectional view showing the appearance of a sound-absorbing material of a ninth embodiment. A cross-sectional view showing the appearance of a sound-absorbing material of the tenth embodiment. A cross-sectional view showing the appearance of a sound-absorbing material of an eleventh embodiment. A cross-sectional view showing the appearance of a sound-absorbing material of the twelfth embodiment. A cross-sectional view showing the appearance of a sound-absorbing material of the thirteenth embodiment. A cross-sectional view showing the appearance of a sound-absorbing material of the fourteenth embodiment. A cross-sectional view showing the appearance of a sound-absorbing material of the fifteenth embodiment. A cross-sectional view showing the appearance of a sound-absorbing material of the sixteenth embodiment. A cross-sectional view showing the appearance of a sound-absorbing material of the seventeenth embodiment. A cross-sectional view showing the appearance of the sound-absorbing material of the eighteenth embodiment. FIG. 1 shows a finite element model of the sound-absorbing material used in Numerical Analysis 1. 1A and 1B are diagrams showing sound pressure distribution and particle velocity distribution obtained in Numerical Analysis 1. 1 is a cross-sectional view showing the normal incidence sound absorption coefficient measuring device used in Experiment 1, cut along a plane including the center line of an acoustic tube. FIG. 1 is a perspective view showing samples (samples of Comparative Example 1 and Examples 1.1 to 1.3) used in Experiment 1. 1 is a graph showing the normal incidence sound absorption coefficient of each sample (samples of Comparative Example 1 and Examples 1.1 to 1.3) measured in Experiment 1. Photographs of samples used in Experiment 2 (samples of Comparative Example 2 and Examples 2.1 and 2.2). 1 is a graph showing the reverberation chamber sound absorption coefficient of each sample (samples of Comparative Example 2 and Examples 2.1 and 2.2) measured in Experiment 2. FIG. 1 is a cross-sectional view showing samples (samples of Comparative Example 3 and Examples 3.1 and 3.2) used in Experiment 3. 1 is a graph showing the reverberation chamber sound absorption coefficient of each sample (samples of Comparative Example 3 and Examples 3.1 and 3.2) measured in Experiment 3. FIG. 11 is a perspective view showing samples (samples of Examples 4.1 to 4.9) defined in Numerical Analysis 2. 1 is a graph showing the normal incidence sound absorption coefficient of each sample (samples of Comparative Example 4 and Examples 4.1 to 4.9) obtained by Numerical Analysis 2. FIG. 11 is a perspective view showing the samples (samples of Examples 5.1 to 5.5) defined in Numerical Analysis 3. 1 is a graph showing the normal incidence sound absorption coefficient of each sample (samples of Comparative Example 5 and Examples 5.1 to 5.5) obtained by Numerical Analysis 3. FIG. 13 is a perspective view showing samples (samples of Comparative Example 6 and Examples 6.1 and 6.2) used in Experiment 4. 1 is a graph showing the normal incidence sound absorption coefficient of each sample (samples of Comparative Example 6 and Examples 6.1 and 6.2) measured in Experiment 4. 13A and 13B are diagrams showing modified examples of the sound insulating portion. 13 is a diagram showing still another modified example of the sound insulating portion. FIG.

1. Sound-absorbing material of the present invention A preferred embodiment of the sound-absorbing material of the present invention will be described in more detail with reference to the drawings. In the following, the sound-absorbing material of the present invention will be described using 18 embodiments of the sound-absorbing material from the first embodiment to the eighteenth embodiment as examples, but the technical scope of the sound-absorbing material of the present invention is not limited to these embodiments. The configuration of the sound-absorbing material of the present invention can be appropriately changed within a range that does not impair the gist of the invention.

1.1 Sound-absorbing material of the first embodiment First, the sound-absorbing material of the first embodiment will be described. Fig. 4 is a perspective view showing the appearance of the sound-absorbing material 10 of the first embodiment. Fig. 5 is a cross-sectional view showing the sound-absorbing material 10 of the first embodiment cut in a cross section perpendicular to its surface _α1 . Fig. 6 is a photograph of the appearance of the sound-absorbing material 10 of the first embodiment.

As shown in Fig. 5, the sound-absorbing material 10 of the first embodiment absorbs incident sound waves 50 that are incident on the sound-absorbing material body 11 from the surface _α1 side. As shown in Figs. 4 to 6, this sound-absorbing material 10 is composed of a sound-absorbing material body 11 that has air permeability (sound absorption properties) and a sound-insulating part 12 that has no air permeability (sound insulation properties).

The sound-insulating portion 12 may be provided on both surfaces _α1 and _α2 of the sound-absorbing material body 11, but in the sound-absorbing material 10 of the first embodiment, it is provided on only one surface, _α1 . In other words, of the pair of surfaces _α1 and _α2 of the sound-absorbing material body 11, only the surface _α1 on which the incident sound wave 50 is incident is the "sound-insulating portion arrangement surface." The sound-insulating portion 12 is not arranged so as to cover the entire area of the surface _α1 of the sound-absorbing material body 11, but is arranged locally so that at least a part of the area of the surface _α1 is exposed when viewed from the surface _α1 side.

The sound-insulating portion 12 may be provided at only one location on the sound-insulating portion mounting surface _α1 of one sound-absorbing material 10. However, in the sound-absorbing material 10 of the first embodiment, a plurality of sound-insulating portions 12 are repeatedly arranged on the sound-insulating portion mounting surface _α1 with gaps between them. By repeatedly providing a plurality of sound-insulating portions 12 in this manner, the diffraction phenomenon described below occurs equally at every location on the sound-insulating portion mounting surface _α1 , and it becomes possible to obtain substantially uniform sound-absorbing characteristics throughout the sound-absorbing material 10.

5, in the sound-absorbing material 10 of the first embodiment, incident sound waves 50 incident on the sound-absorbing material body 11 from the surface _α1 side can be diffracted by the sound-insulating parts 12. This makes it possible to lengthen the path length of the incident sound waves 50 inside the sound-absorbing material body 11, and to increase the apparent thickness of the sound-absorbing material body 11.

As already mentioned, in a typical sound absorbing material, the sound absorption coefficient becomes high when the thickness is equal to 1/4 of the wavelength of the incident sound wave. However, in the sound absorbing material 10 of the first embodiment and the sound absorbing material 10 of the present invention, the apparent thickness of the sound absorbing material body 11 becomes large due to the diffraction phenomenon described above, so that the frequency band in which the sound absorption coefficient becomes high can be shifted to the lower frequency side. Therefore, sound can be effectively absorbed in the low frequency band without making the sound absorbing material body 11 thick. For example, although it depends on the material of the sound absorbing material body 11, even if the thickness of the sound absorbing material body 11 is 40 mm or less or 30 mm or less, it is possible to effectively absorb sound in the low frequency band.

Examples of materials (breathable materials) that form the sound-absorbing body 11 include foamed resins (open-cell type) such as urethane foam and polyethylene foam, and porous materials such as nonwoven fabrics such as chemical fiber felt and natural fiber felt. There are no particular limitations on the shape of the sound-absorbing body 11. In the sound-absorbing material 10 shown in Figures 4 to 6, the sound-absorbing body 11 is a flat plate-shaped member made of urethane foam.

On the other hand, examples of the material (non-breathable material) forming the sound insulation part 12 include a plate material or sheet material made of rubber, resin, metal, etc. The sound insulation part 12 can be provided as a patch-shaped member, or can be provided as a paint-based material applied to the sound insulation part arrangement surface α ₁ of the sound absorbing material body 11, or as a molten film part locally formed on the sound insulation part arrangement surface α ₁ of the sound absorbing material body 11. The shape (shape in plan view) of the sound insulation part 12 is not particularly limited, and various shapes such as a polygon such as a rectangle, a circle, an ellipse, etc. can be adopted. In the sound absorbing material 10 shown in Figures 4 to 6, the sound insulation part 12 is a square (rectangular) sheet material formed of rubber.

As described above, the sound-absorbing material body 11 is formed of a breathable material (a material with low flow resistance). In this regard, in consideration of the sound absorbing properties of the sound-absorbing material body 11, the flow resistance (airflow resistance) of the sound-absorbing material body is preferably 10 ⁷ N·s/m ⁴ or less. The flow resistance of the sound-absorbing material body is more preferably 10 ⁶ N·s/m ⁴ or less, and even more preferably 10 ⁵ N·s/m ⁴ or less.

However, if the flow resistance of the sound-absorbing material body is made too low, the sound-absorbing performance of the sound-absorbing material body may be reduced. For this reason, the flow resistance of the sound-absorbing material body is preferably ¹⁰ N·s/ ^m4 or more. The flow resistance of the sound-absorbing material body is more preferably 10 2 N·s/ ^m4 or more, and even more preferably 10 ³ N·s/ ^m4 or more. In the sound-absorbing material 10 shown in Figures 4 to ⁶ , the flow resistance of the sound-absorbing material body 11 is 1.1 x 10 ⁴ N·s/m4.

On the other hand, the sound insulation part 12 is formed of a material having no air permeability (a material having a large flow resistance). In this regard, in consideration of the ease of diffraction in the sound insulation part 12, the flow resistance (air flow resistance) of the sound insulation part 12 is preferably 10 ⁸ N·s/m ⁴ or more. The flow resistance of the sound insulation part is more preferably 10 ⁹ N·s/m ⁴ or more, and even more preferably 10 ¹⁰ N·s/m ⁴ or more. If the sound insulation part is formed of a completely air-impermeable material, the flow resistance of the sound insulation part becomes infinite. In the sound absorbing material 10 shown in Figs. 4 to 6, the flow resistance of the sound insulation part 12 is 5.62 x 10 ⁸ N·s/m ⁴ (the measurement limit value of the measuring device used) or more.

The acoustic characteristics of the sound-absorbing material body 11 are not particularly limited. However, if the porosity (porosity) of the sound-absorbing material body 11 is too small, the flow resistance (airflow resistance) increases and sound waves do not penetrate the sound-absorbing material body 11, making it difficult to ensure the sound absorption properties of the sound-absorbing material body 11. For this reason, the porosity of the sound-absorbing material body 11 is preferably 0.7 or more. The porosity of the sound-absorbing material body 11 is more preferably 0.8 or more, and even more preferably 0.9 or more.

However, if the porosity of the sound-absorbing material body 11 is too close to 1 (the value when the sound-absorbing material body is entirely air), it becomes difficult to ensure the sound-absorbing properties of the sound-absorbing material body 11. For this reason, it is preferable that the porosity of the sound-absorbing material body 11 is 0.999 or less. It is more preferable that the porosity of the sound-absorbing material body 11 is 0.998 or less, and even more preferable that the porosity of the sound-absorbing material body 11 is 0.994 or less. In the sound-absorbing material 10 shown in Figures 4 to 6, the porosity of the sound-absorbing material body 11 is 0.986.

On the other hand, the surface density of the sound-insulating part 12 varies depending on whether the sound-insulating part 12 is integrated with the sound-absorbing material body 11 or not, and is not particularly limited. This is because, if the surface density of the sound-insulating part 12 is small, the sound waves will cause the sound-insulating part 12 to vibrate significantly, and the sound will be re-radiated to the opposite side from the vibration, making it easier for the sound to pass through, making it difficult to ensure the sound insulation of the sound-insulating part 12. If the sound-insulating part 12 is not integrated with the sound-absorbing material body 11, the sound insulation must be ensured by the mass and rigidity of the sound-insulating part 12 itself, so the surface density of the sound-insulating part 12 needs to be increased, whereas if the sound-insulating part 12 is integrated with the sound-absorbing material body 11, the mass and rigidity of the sound-absorbing material body 11 will make it difficult for the sound-insulating part 12 to vibrate, so the surface density of the sound-insulating part 12 can be reduced.

Considering the above, when the sound insulation part 12 is integrated with the sound-absorbing material body 11, the surface density of the sound insulation part is preferably 0.01 kg/ ^m2 or more. In this case, the surface density of the sound insulation part is more preferably 0.05 kg/ ^m2 or more, and further preferably 0.1 kg/ ^m2 or more.

On the other hand, when the sound-insulating portion 12 is not integrated with the sound-absorbing material body 11, the surface density is preferably 0.1 kg/m2 or ^more . In this case, the surface density of the sound-insulating portion is more preferably 0.5 kg/ ^m2 or more, and even more preferably 1.0 kg/m2 or ^more . There is no particular upper limit to the surface density of the sound-insulating portion 12, but it is usually 50 kg/ ^m2 or less. In the sound-absorbing material 10 shown in Figures 4 to 6, the surface density of the sound-insulating portion 12 is 2.24 kg/ ^m2 .

As already described, the sound-insulating parts 12 are provided locally on the sound-insulating part arrangement surface _α1 of the sound-absorbing material body 11. There is no particular limitation on the proportion of the sound-insulating parts 12 provided on the sound-insulating part arrangement surface _α1 of the sound-absorbing material body 11. However, if the proportion of the sound-insulating parts 12 provided is too small, there is a risk that the above-mentioned diffraction phenomenon will not easily occur. For this reason, it will be difficult to shift the frequency band in which the sound absorption coefficient becomes high to the lower frequency side.

Therefore, the ratio _S2 /S1 of the total area _S2 of the sound insulating parts 12 arranged on the sound insulating part arrangement surface _α1 of the sound absorbing material body ₁₁ to the area _S1 of the sound insulating part arrangement surface _α1 is preferably 0.1 or more. The ratio _S2 / _S1 is more preferably 0.2 or more, and even more preferably 0.3 or more.

However, if the ratio _S2 / _S1 is too large, as will be explained in the experimental results below, the frequency band where the sound absorption coefficient is high shifts to the lower frequency side, but a sharp sound absorption peak is formed near that frequency, narrowing the frequency range where a high sound absorption coefficient is obtained. This is thought to be because if the ratio _S2 / _S1 is too large, the above-mentioned diffraction phenomenon does not occur, but Helmholtz resonance occurs, the same as in the perforated panel sound absorbing structure. Therefore, it is preferable to keep the ratio _S2 / _S1 to a level where Helmholtz resonance does not occur (for example, 0.99 or less).

Furthermore, when multiple sound-insulating parts 12 are repeatedly arranged as in the sound-absorbing material 10 of the first embodiment, the width of the gap between adjacent sound-insulating parts 12 also affects the sound-absorbing characteristics of the sound-absorbing material 10. That is, if this gap is narrow, the above-mentioned ratio _S2 / _S1 inevitably becomes large, and the above-mentioned Helmholtz resonance occurs instead of diffraction, narrowing the frequency range at which a high sound absorption coefficient can be obtained.

Therefore, the width of the gap between adjacent sound-proofing parts 12 is usually 1 mm or more. The width of the gap between adjacent sound-proofing parts 12 is preferably 3 mm or more, and more preferably 5 mm or more. There is no particular upper limit to the width of the gap between adjacent sound-proofing parts 12, but it is usually about 100 to 300 mm.

Furthermore, as will be explained in the experimental results below, the dimensions of the sound-insulating parts 12 also affect the sound-absorbing properties of the sound-absorbing material 10. In other words, as the dimensions of each sound-insulating part 12 become larger, sound can be effectively absorbed from lower frequencies. For this reason, it is preferable to make the dimensions of each sound-insulating part 12 somewhat larger.

The specific dimensions of the sound insulation parts 12 vary depending on the material and shape of the sound insulation parts 12, but the span (equivalent circular diameter) of each sound insulation part 12 is usually set to 10 mm or more. The span of each sound insulation part 12 is preferably 20 mm or more, more preferably 30 mm or more, and even more preferably 40 mm or more. There is no particular upper limit to the span of each sound insulation part 12, but it is usually up to about 500 mm.

1.2 Sound-absorbing material of the second embodiment Next, the sound-absorbing material of the second embodiment will be described. Fig. 7 is a perspective view showing the appearance of the sound-absorbing material of the second embodiment. In the sound-absorbing material 10 of the first embodiment described above (Fig. 4), the sound-insulating portion 12 is rectangular, but in the sound-absorbing material 10 of the second embodiment, as shown in Fig. 7, the sound-insulating portion 12 is circular. In this way, the shape of the sound-insulating portion 12 can be a shape other than a rectangular shape. For configurations not specifically mentioned in the sound-absorbing material 10 of the second embodiment, the same configurations as those described in the sound-absorbing material 10 of the first embodiment can be adopted.

1.3 Sound-absorbing material of the third embodiment Next, the sound-absorbing material of the third embodiment will be described. FIG. 8 is a perspective view showing the appearance of the sound-absorbing material of the third embodiment. In the sound-absorbing material 10 of the first embodiment (FIG. 4) and the sound-absorbing material 10 of the second embodiment (FIG. 8) described above, the sound-insulating part 12 has only one shape, but in the sound-absorbing material 10 of the third embodiment, as shown in FIG. 8, the sound-insulating part 12 is a mixture of a square shape and a circular shape. In this way, by combining a plurality of types of sound-insulating parts 12 of different shapes, it is possible to provide a variation in the diffraction distance, and it is possible to make the sound absorption coefficient high not only around one frequency but also around a plurality of frequencies. For the configurations not specifically mentioned in the sound-absorbing material 10 of the third embodiment, the same configurations as those described in the sound-absorbing material 10 of the other embodiments can be adopted.

1.4 Sound-absorbing material of the fourth embodiment Next, the sound-absorbing material of the fourth embodiment will be described. FIG. 9 is a perspective view showing the appearance of the sound-absorbing material of the fourth embodiment. In the sound-absorbing material 10 of the first embodiment (FIG. 4) and the sound-absorbing material 10 of the second embodiment (FIG. 8) described above, the sound-insulating portion 12 has only one size. In the sound-absorbing material 10 of the fourth embodiment, as shown in FIG. 9, the sound-insulating portion 12 has a variety of sizes (large sizes and small sizes). In this way, by combining a plurality of types of sound-insulating portions 12 of different sizes, it is possible to vary the diffraction distance, and it is possible to increase the sound absorption coefficient not only around one frequency but also around a plurality of frequencies. For the configurations not specifically mentioned in the sound-absorbing material 10 of the fourth embodiment, the same configurations as those described in the sound-absorbing material 10 of the other embodiments can be adopted.

1.5 Sound-absorbing material of the fifth embodiment Next, the sound-absorbing material of the fifth embodiment will be described. Fig. 10 is a perspective view showing the appearance of the sound-absorbing material of the fifth embodiment. In the sound-absorbing materials 10 of the first to fourth embodiments described above (Figs. 4 and 7 to 9), the multiple sound-insulating parts 12 are regularly arranged on the lattice points of a square lattice, whereas in the sound-absorbing material 10 of the fifth embodiment, as shown in Fig. 10, the multiple sound-insulating parts 12 are irregularly (randomly) arranged. For configurations not specifically mentioned in the sound-absorbing material 10 of the fifth embodiment, the same configurations as those described in the sound-absorbing materials 10 of the other embodiments can be adopted.

1.6 Sound-absorbing material of the sixth embodiment Next, the sound-absorbing material of the sixth embodiment will be described. FIG. 11 is a perspective view showing the appearance of the sound-absorbing material of the sixth embodiment. In the sound-absorbing material 10 of the first to fifth embodiments described above (FIGS. 4 and 7 to 10), the patch-shaped sound-insulating parts 12 are repeatedly arranged in two directions (vertical and horizontal directions), whereas in the sound-absorbing material 10 of the sixth embodiment, as shown in FIG. 11, the sound-insulating parts 12 extending in a strip shape in one direction (vertical direction) are repeatedly arranged in the other direction (horizontal direction). The adjacent sound-insulating parts 12 are arranged approximately parallel to each other, and the gap between them is formed in a slit shape. For the configurations of the sound-absorbing material 10 of the sixth embodiment that are not particularly mentioned, the same configurations as those described for the sound-absorbing material 10 of the other embodiments can be adopted.

1.7 Sound-absorbing material of the seventh embodiment Next, the sound-absorbing material of the seventh embodiment will be described. Fig. 12 is a perspective view showing the appearance of the sound-absorbing material of the seventh embodiment. In the sound-absorbing materials 10 of the first to sixth embodiments described above (Figs. 4 and 7 to 11), a plurality of sound-insulating parts 12 are arranged on one sound-absorbing material body 11, but in the sound-absorbing material 10 of the seventh embodiment, as shown in Fig. 12, only one sound-insulating part 12 is arranged on one sound-absorbing material body 11. For configurations not specifically mentioned in the sound-absorbing material 10 of the seventh embodiment, the same configurations as those described in the sound-absorbing materials 10 of the other embodiments can be adopted.

1.8 Sound-absorbing material of the eighth embodiment Next, the sound-absorbing material of the eighth embodiment will be described. FIG. 13 is a cross-sectional view showing the appearance of the sound-absorbing material of the eighth embodiment. In the sound-absorbing material 10 of the first to seventh embodiments described above (FIGS. 4 and 7 to 12), nothing was arranged on the surface of the sound-insulating part 12 opposite to the sound-absorbing material body 11. In the sound-absorbing material 10 of the eighth embodiment, as shown in FIG. 13, a sound-absorbing covering material 13 made of a thick breathable material (urethane foam, etc.) is arranged on the surface of the sound-insulating part 12 opposite to the sound-absorbing material body 11. This makes it possible to improve sound absorption in the high frequency band, as will be described in Experiment 3 below. For the configurations not specifically mentioned in the sound-absorbing material 10 of the eighth embodiment, the same configurations as those described in the sound-absorbing material 10 of the other embodiments can be adopted.

1.9 Sound-absorbing material of the ninth embodiment Next, the sound-absorbing material of the ninth embodiment will be described. FIG. 14 is a cross-sectional view showing the appearance of the sound-absorbing material of the ninth embodiment. In the sound-absorbing material 10 of the first to seventh embodiments described above (FIGS. 4 and 7 to 12), nothing was arranged on the surface of the sound-insulating part 12 opposite to the sound-absorbing material body 11. In the sound-absorbing material 10 of the ninth embodiment, as shown in FIG. 14, a sound-absorbing covering material 13 made of a thin breathable material (nonwoven fabric film such as melt-blown nonwoven fabric) is arranged on the surface of the sound-insulating part 12 opposite to the sound-absorbing material body 11. This makes it possible to absorb sound from a lower frequency side, as will be described in Experiment 4 below. For configurations not specifically mentioned in the sound-absorbing material 10 of the ninth embodiment, the same configurations as those described in the sound-absorbing material 10 of the other embodiments can be adopted.

1.10 Sound-absorbing material of the tenth embodiment Next, the sound-absorbing material of the tenth embodiment will be described. Fig. 15 is a cross-sectional view showing the appearance of the sound-absorbing material of the tenth embodiment. In the sound-absorbing materials 10 of the first to ninth embodiments (Figs. 4 and 7 to 14) described above, except for the sound-absorbing material 10 of the seventh embodiment (Fig. 12) (those having a plurality of sound-insulating parts 12), the sound-absorbing material body 11 overlapping one sound-insulating part 12 and the sound-absorbing material body 11 overlapping another sound-insulating part 12 are continuous, whereas in the sound-absorbing material 10 of the tenth embodiment, as shown in Fig. 15, the sound-absorbing material body 11 overlapping one sound-insulating part 12 and the sound-absorbing material body 11 overlapping another sound-insulating part 12 are separated. In other words, the sound-absorbing material body 11 is arranged only around the part overlapping the sound-insulating part 12, and the sound-absorbing material body 11 is not arranged in the part overlapping the gap of the sound-insulating part 12. For configurations of the sound-absorbing material 10 of the tenth embodiment that are not specifically mentioned, configurations similar to those described for the sound-absorbing materials 10 of the other embodiments can be adopted.

1.11 Sound-absorbing material of eleventh embodiment Next, the sound-absorbing material of the eleventh embodiment will be described. Fig. 16 is a cross-sectional view showing the appearance of the sound-absorbing material of the eleventh embodiment. In the sound-absorbing material 10 of the tenth embodiment, as shown in Fig. 16, an air layer 14 is provided on the back side of the sound-absorbing material 10 (the surface _α2 side of the sound-absorbing material body 11). In this way, the air layer 14 can also be provided on the surface _α2 side (transmission side) of the sound-absorbing material 10. For configurations not specifically mentioned in the sound-absorbing material 10 of the eleventh embodiment, the same configurations as those described in the sound-absorbing materials 10 of the other embodiments can be adopted.

1.12 Sound-absorbing material of the twelfth embodiment Next, the sound-absorbing material of the twelfth embodiment will be described. Fig. 17 is a cross-sectional view showing the appearance of the sound-absorbing material of the twelfth embodiment. In the sound-absorbing material 10 of the eleventh embodiment (Fig. 16) described above, the sound-absorbing material body 11 overlapping one sound-insulating part 12 and the sound-absorbing material body 11 overlapping the other sound-insulating part 12 are continuous, whereas in the sound-absorbing material 10 of the twelfth embodiment, as shown in Fig. 17, the sound-absorbing material body 11 overlapping one sound-insulating part 12 and the sound-absorbing material body 11 overlapping the other sound-insulating part 12 are separated. In other words, the sound-absorbing material 10 of the twelfth embodiment is a combination of the sound-absorbing material 10 of the eleventh embodiment (Fig. 16) and the structure of the sound-absorbing material 10 of the tenth embodiment (Fig. 15). For the structures not specifically mentioned in the sound-absorbing material 10 of the twelfth embodiment, the same structures as those described in the sound-absorbing material 10 of the other embodiments can be adopted.

1.13 Sound-absorbing material of thirteenth embodiment Next, the sound-absorbing material of the thirteenth embodiment will be described. Fig. 18 is a cross-sectional view showing the appearance of the sound-absorbing material of the thirteenth embodiment. In the sound-absorbing materials 10 of the first to twelfth embodiments described above (Figs. 4 and 7 to 17), the sound-insulating portion 12 is provided on the front side (the surface _α1 side where sound is incident) of the sound-absorbing material body 11, whereas in the sound-absorbing material 10 of the thirteenth embodiment, as shown in Fig. 18, the sound-insulating portion 12 is provided on the back side (the surface _α2 side where sound is transmitted) of the sound-absorbing material body 11. For configurations not specifically mentioned in the sound-absorbing material 10 of the thirteenth embodiment, the same configurations as those described in the sound-absorbing materials 10 of the other embodiments can be adopted.

1.14 Sound-absorbing material of the fourteenth embodiment Next, the sound-absorbing material of the fourteenth embodiment will be described. Fig. 19 is a cross-sectional view showing the appearance of the sound-absorbing material of the fourteenth embodiment. In the sound-absorbing material 10 of the thirteenth embodiment (Fig. 18) described above, the sound-absorbing material body 11 overlapping one sound-insulating part 12 and the sound-absorbing material body 11 overlapping the other sound-insulating part 12 are continuous, whereas in the sound-absorbing material 10 of the fourteenth embodiment, as shown in Fig. 19, the sound-absorbing material body 11 overlapping one sound-insulating part 12 and the sound-absorbing material body 11 overlapping the other sound-insulating part 12 are separated. In other words, the sound-absorbing material 10 of the fourteenth embodiment is a combination of the sound-absorbing material 10 of the thirteenth embodiment (Fig. 18) and the structure of the sound-absorbing material 10 of the tenth embodiment (Fig. 15). For the structures not specifically mentioned in the sound-absorbing material 10 of the fourteenth embodiment, the same structures as those described in the sound-absorbing material 10 of the other embodiments can be adopted.

1.15 Sound-absorbing material of the fifteenth embodiment Next, the sound-absorbing material of the fifteenth embodiment will be described. FIG. 20 is a cross-sectional view showing the appearance of the sound-absorbing material of the fifteenth embodiment. In the sound-absorbing materials 10 of the first to fourteenth embodiments described above (FIGS. 4 and 7 to 19), the sound-absorbing material body 11 has a single-layer structure, whereas in the sound-absorbing material 10 of the fifteenth embodiment, as shown in FIG. 20, the sound-absorbing material body 11 has a multi-layer structure. Specifically, the sound-absorbing material body 11 is formed by laminating a plurality of types of sound-absorbing materials 11a, 11b, and 11c having different flow resistances. In the example shown in FIG. 20, the sound-absorbing material body 11 has a three-layer structure, but the sound-absorbing material body 11 can also have two layers or four or more layers. For the configurations not specifically mentioned in the sound-absorbing material 10 of the fifteenth embodiment, the same configurations as those described in the sound-absorbing materials 10 of the other embodiments can be adopted.

1.16 Sound-absorbing material of the sixteenth embodiment Next, the sound-absorbing material of the sixteenth embodiment will be described. Fig. 21 is a cross-sectional view showing the appearance of the sound-absorbing material of the sixteenth embodiment. In the sound-absorbing material 10 of the sixteenth embodiment, as shown in Fig. 21, the sound-absorbing material body 11 has a multi-layer structure, and an air layer 14 is provided on the back side of the sound-absorbing material 10 (the surface _α2 side of the sound-absorbing material body 11). In other words, the sound-absorbing material 10 of the sixteenth embodiment is a combination of the sound-absorbing material 10 of the fifteenth embodiment (Fig. 20) and the sound-absorbing material 10 of the eleventh embodiment (Fig. 16). For the configurations of the sound-absorbing material 10 of the sixteenth embodiment that are not particularly mentioned, the same configurations as those described for the sound-absorbing materials 10 of the other embodiments can be adopted.

1.17 Sound-absorbing material of the seventeenth embodiment Next, the sound-absorbing material of the seventeenth embodiment will be described. FIG. 22 is a cross-sectional view showing the appearance of the sound-absorbing material of the seventeenth embodiment. As shown in FIG. 22, the sound-absorbing material of the seventeenth embodiment is a laminated type in which two sound-absorbing materials 10 consisting of a sound-absorbing material body 11 and a plurality of sound-insulating parts 12 are laminated in the thickness direction. As in the sound-absorbing material of the seventeenth embodiment, a plurality of sound-absorbing materials 10 can be arranged in layers. This makes it possible to absorb sound from the lower frequency side. The number of layers of the sound-absorbing material 10 is not limited to two, and can be three or more. For the configurations not specifically mentioned in the sound-absorbing material of the seventeenth embodiment, the same configurations as those described in the sound-absorbing materials 10 of the other embodiments can be adopted.

1.18 Sound-absorbing material of the eighteenth embodiment Next, the sound-absorbing material of the eighteenth embodiment will be described. FIG. 23 is a cross-sectional view showing the appearance of the sound-absorbing material of the eighteenth embodiment. In the sound-absorbing material of the seventeenth embodiment (FIG. 22) described above, the sound-insulating parts 12 constituting the sound-absorbing material 10 of different layers are arranged so as to overlap each other in the thickness direction of the sound-absorbing material 10. In the sound-absorbing material of the eighteenth embodiment, as shown in FIG. 23, the sound-insulating parts 12 constituting the sound-absorbing material 10 of different layers are arranged so as not to overlap each other in the thickness direction of the sound-absorbing material 10. This makes it possible to absorb sound from the lower frequency side. It is more preferable that the sound-insulating parts 12 constituting the sound-absorbing material 10 of different layers are arranged so as to be staggered not only in one direction (the left-right direction on the paper surface of FIG. 23) but also in another direction (the direction perpendicular to the paper surface of the same figure). For the configurations not specifically mentioned in the sound-absorbing material of the eighteenth embodiment, the same configurations as those described in the sound-absorbing material 10 of the other embodiments can be adopted.

1.19 Others In the sound absorbing material 10 of the first to eighteenth embodiments described above, the multiple sound insulating parts 12 (patch-like members) are arranged at a distance from each other. However, if the frequency band of sound absorption can be shifted to the lower frequency side by diffracting the incident sound waves in the sound insulating parts 12 according to the above-mentioned principle, these sound insulating parts 12 can be connected to each other. FIG. 39 is a diagram showing a modified example of the sound insulating part 12. FIG. 40 is a diagram showing another modified example of the sound insulating part 12. The sound insulating parts 12 shown in FIG. 39 and FIG. 40 are formed by repeatedly arranging square parts in a checkerboard pattern. In the sound insulating part 12 of FIG. 39, the corner vertices of each square part are connected in a dot-like manner, and in the sound insulating part 12 of FIG. 40, the corners of each square part are connected in a slightly overlapping manner. 39 and 40, the units forming the sound insulation parts 12 are rectangular, but the shapes of the units forming the sound insulation parts 12 may be other than rectangular (for example, circular or elliptical). Also, a combination of a plurality of different shapes may be used.

2. Numerical Analyses and Experiments In order to confirm the effectiveness of the sound-absorbing material of the present invention, the following Numerical Analyses 1 to 4 and Experiments 1 to 3 were carried out.

2.1 Numerical analysis 1
First, in the sound-absorbing material of the present invention, Numerical Analysis 1 was performed to confirm how incident sound waves propagate inside the sound-absorbing material body. This Numerical Analysis 1 as well as Numerical Analysis 2 to 3 described below were performed using FEM (Finite Element Method). The acoustic analysis software used was "Simcenter3D" manufactured by Siemens. FIG. 24 shows a finite element model of the sound-absorbing material used in Numerical Analysis 1. Numerical Analysis 1 was performed for two cases, one where the thickness of the sound-absorbing material body was set to 20 mm and the other where it was set to 60 mm.

FIG. 25 shows the sound pressure distribution and particle velocity distribution obtained in the numerical analysis 1. FIG. 25(a) and (b) show the results when the thickness of the sound absorbing material body is set to 20 mm, of which FIG. 25(a) shows the sound pressure distribution and FIG. 25(b) shows the particle velocity distribution. FIG. 25(c) and (d) show the results when the thickness of the sound absorbing material body is set to 60 mm, of which FIG. 25(c) shows the sound pressure distribution and FIG. 25(d) shows the particle velocity distribution. From FIG. 25, it can be seen that the incident sound wave is diffracted at the edge of the sound insulation part and goes around to the back side of the sound insulation part. It can also be seen that the degree of diffraction is greater when the thickness of the sound absorbing material body is small (FIG. 25(b)) than when the thickness of the sound absorbing material body is large (FIG. 25(d)). As already mentioned, the reason why the sound-absorbing material of the present invention is able to absorb sound from low frequencies is that the sound waves incident on the main body of the sound-absorbing material are diffracted at the sound-insulating part, thereby lengthening the path length of the incident sound waves inside the main body of the sound-absorbing material. This phenomenon is supported by the results of Numerical Analysis 1.

2.2 Experiment 1
Next, experiment 1 was carried out to measure the normal incidence sound absorption coefficient of the sound absorbing material according to the present invention. Fig. 26 is a cross-sectional view showing the normal incidence sound absorption coefficient measuring device used in experiment 1 cut along a plane including the center line of the sound tube. As shown in Fig. 26, a disk-shaped sample (sound absorbing material) was placed in the middle of the inside of a cylindrical sound tube with an inner diameter of 100 mm, and sound waves were perpendicularly incident on the sample (sound absorbing material) from a sound source provided at one end of the sound tube, and the intensity of the reflected wave was detected by a microphone placed between the sound source and the sample (sound absorbing material), thereby obtaining the reflectance of the sample (sound absorbing material) and calculating the normal incidence sound absorption coefficient.

Figure 27 is a perspective view showing the samples (samples of Comparative Example 1 and Examples 1.1 to 1.3) used in Experiment 1. As shown in Figure 27, the sound-absorbing material according to the present invention (samples of Examples 1.1 to 1.3) is composed of a disk-shaped sound-absorbing material body with an outer diameter of 100 mm and a thickness of 20 mm, and a circular sound-insulating part provided in the center of one side (the side on which sound waves are incident) of the sound-absorbing material body. The diameter of the sound-insulating part is 40 mm in the sample of Example 1.1, 60 mm in the sample of Example 1.2, and 80 mm in the sample of Example 1. The sound-absorbing material body is made of urethane foam, and the sound-insulating part is made of a rubber sheet. In Experiment 1, in order to confirm the effectiveness of the sound-absorbing material of the present invention, the same measurements were also performed on the sample of Comparative Example 1 that does not have a sound-insulating part. The dimensions and material of the sound-absorbing material body in the sample of Comparative Example 1 are the same as those of the sound-absorbing material body used in Examples 1.1 to 1.3.

FIG. 28 shows a graph of the normal incidence sound absorption coefficient of each sample (samples of Comparative Example 1 and Examples 1.1 to 1.3) measured in Experiment 1. From FIG. 28, it can be seen that the sound absorbing material according to the present invention (samples of Examples 1.1 to 1.3) has a higher sound absorption coefficient in the low frequency range than the sample of Comparative Example 1. From this, it was found that the sound absorbing material of the present invention can absorb sound from the low frequency range. Also, from FIG. 28, it can be seen that the sample of Example 1.2, whose sound insulation part has a diameter of 60 mm, absorbs sound from the low frequency range more than the sample of Example 1.1, whose sound insulation part has a diameter of 40 mm, and further, the sample of Example 1.3, whose sound insulation part has a diameter of 80 mm, absorbs sound from the low frequency range more than the sample of Example 1.2, whose sound insulation part has a diameter of 60 mm. From this, it can be seen that sound can be absorbed from a lower frequency range by increasing the dimensions of the sound insulation part.

2.3 Experiment 2
Next, experiment 2 was carried out to measure the reverberation room sound absorption coefficient of the sound absorbing material according to the present invention. The measurement of the reverberation room sound absorption coefficient in experiment 2 was carried out in accordance with the method standardized in JIS A1409 "Method of measuring reverberation room sound absorption coefficient."

FIG. 29 is a photograph of the samples (samples of Comparative Example 2 and Examples 2.1 and 2.2) used in Experiment 2. The sound-absorbing material according to the present invention (samples of Examples 2.1 and 2.2) is a sound-absorbing material body made of urethane foam with an area of 4 m ² (=2 m×2 m) and a thickness of 20 mm, on one side of which a plurality of rubber sound-insulating parts are arranged on the lattice points of a square lattice. In the sample of Example 2.1, each sound-insulating part is in the shape of a square of 80 mm×80 mm, and in the sample of Example 2.2, each sound-insulating part is in the shape of a square of 200 mm×200 mm. The number of sound-insulating parts and the gaps were set so that the above ratio S ₂ /S ₁ was equal at 0.64 in the samples of Examples 2.1 and 2.2. In Experiment 2, the same measurements were performed on the sample of Comparative Example 2, which was the same as the samples of Examples 2.1 and 2.2, except that no sound-insulating parts were provided.

FIG. 30 shows a graph of the reverberation room sound absorption coefficient of each sample (samples of Comparative Example 2 and Examples 2.1 and 2.2) measured in Experiment 2. From the results of FIG. 30, it can be seen that the sound absorbing material according to the present invention (samples of Examples 2.1 and 2.2) can absorb sound from a lower frequency band. Furthermore, from a comparison of the measurement results for the samples of Examples 2.1 and 2.2, it was found that even if the ratio _S2 / _S1 is constant, the larger the dimensions of each sound insulation part, the more sound can be absorbed from a lower frequency band. Note that in FIG. 30, there are some places (for example, the 1000 Hz, 1250 Hz, and 1600 Hz bands in Example 2.1) where the sound absorption coefficient exceeds 1 (the absorbed energy is greater than the energy of the incident sound), but this is due to the area effect that occurs because the test specimen area is smaller than the 10 ^m2 specified by the standard. If a measurement is performed using a larger test specimen, the sound absorption coefficient will be smaller than this measured value, but it is considered that the relationship between the test specimens will not change.

2.4 Experiment 3
Next, experiment 3 was conducted to measure the reverberation chamber sound absorption coefficient of a sample in which two sheets of urethane foam (sound-absorbing material body or sound-absorbing covering material) were stacked, similar to experiment 2. Figure 31 is a cross-sectional view showing the samples (samples of Comparative Example 3, Example 3.1, and Example 3.2) used in experiment 3. The sample of Example 3.1 is a sample in which the sound-absorbing material body is composed of two sheets of urethane foam with a thickness of 20 mm stacked, and a sound-insulating part having a square shape of 200 mm x 200 mm is arranged on the lattice points of a rectangular lattice on the surface layer of the sound-absorbing material body. The sample of Example 3.2 is a sample in which a sound-insulating part having a square shape of 200 mm x 200 mm is arranged on the lattice points of a rectangular lattice on the surface layer of a single sound-absorbing material body made of urethane foam with a thickness of 20 mm, and the surface of the sound-insulating part opposite to the sound-absorbing material body is covered with a single sound-absorbing covering material made of urethane foam with a thickness of 20 mm. The sample of Example 3.2 can be regarded as a sample in which a sound-insulating portion is disposed between two sheets of urethane foam (middle layer). Furthermore, the sample of Comparative Example 3 is a sample in which the sound-insulating portion is removed from the sample of Example 3.1.

Fig. 32 shows a graph of the reverberation room sound absorption coefficient of each sample (samples of Comparative Example 3 and Examples 3.1 and 3.2) measured in Experiment 3. As can be seen from Fig. 32, the sample of Example 3.2 in which the sound insulation part is arranged in the middle layer has an improved sound absorption coefficient in the high frequency band compared to the sample of Example 3.1 in which the sound insulation part is arranged in the surface layer. From this, it was found that by covering the surface of the sound insulation part opposite to the sound absorbing material body with a breathable sound absorbing covering material (a structure in which the sound insulation part is sandwiched between materials having sound absorption properties), an excellent sound absorption effect can be achieved in a wide range from low to high frequency bands.

2.5 Numerical Analysis 2
Next, Numerical Analysis 2 was performed to confirm the dependency of the ratio _S2 / _S1 on the normal incidence sound absorption coefficient. Fig. 33 is a perspective view showing the samples defined in Numerical Analysis 2 (samples of Examples 4.1 to 4.9). In the samples of Examples 4.1 to 4.9, the sound-insulating portion was defined as a square shape of 100 mm x 100 mm, and the sound-absorbing material body was defined as a fiber-based sound-absorbing material having a thickness of 20 mm. In the samples of Examples 4.1 to 4.9, the area of the sound-insulating portion was kept constant, but the area of the sound-absorbing material body was changed to vary the ratio _S2 / _S1 . The value of the ratio _S2 / _S1 is about 0.995 for the sample of Example 4.1, about 0.990 for the sample of Example 4.2, about 0.980 for the sample of Example 4.3, about 0.943 for the sample of Example 4.4, about 0.907 for the sample of Example 4.5, about 0.640 for the sample of Example 4.6, about 0.503 for the sample of Example 4.7, about 0.401 for the sample of Example 4.8, and about 0.200 for the sample of Example 4. The sample of Comparative Example 4 is the sample of Example 4.1 without the sound insulating portion.

FIG. 34 shows a graph of the normal incidence sound absorption coefficient of each sample (samples of Comparative Example 4 and Examples 4.1 to 4.9) obtained by Numerical Analysis 2. As shown in FIG. 34, the smaller the ratio S ₂ /S ₁ , the wider the frequency band including the low frequency band is in which the sound absorption effect occurs. Specifically, in the samples of Examples 4.3 to 4.9 in which the ratio S ₂ /S ₁ is less than 0.990, the sound absorption effect is obtained in a relatively wide frequency band. On the other hand, when the ratio S ₂ /S ₁ is large (for example, the samples of Examples 4.1 and 4.2 in which the ratio S ₂ /S ₁ is 0.990 or more), it was found that although an excellent sound absorption effect is obtained in the frequency band, the frequency range in which such an effect is obtained is narrow. The reason for this is considered to be that, as the ratio S ₂ /S ₁ is increased, the effect of Helmholtz resonance appears more strongly than the effect of the diffraction phenomenon described above.

2.6 Numerical Analysis 3
Next, Numerical Analysis 3 was carried out to confirm the dependency of the dimensions of the sound insulation part and the sound absorbing body on the normal incidence sound absorption coefficient when the ratio _S2 / _S1 was constant. Figure 35 is a perspective view showing the samples defined in Numerical Analysis 3 (samples of Examples 5.1 to 5.5). In the samples of Examples 5.1 to 5.5, the ratio _S2 / _S1 was constant at 0.5. The sound absorbing body was defined as a fiber-based sound absorbing material with a thickness of 80 mm. However, the dimensions of the sound insulation part and the sound absorbing body were gradually increased from the sample of Example 5.1 to the sample of Example 5.5. That is, in the sample of Example 5.1, the sound insulation part has dimensions of 100 mm x 100 mm, in the sample of Example 5.2, the sound insulation part has dimensions of 150 mm x 150 mm, in the sample of Example 5.3, the sound insulation part has dimensions of 200 mm x 200 mm, in the sample of Example 5.4, the sound insulation part has dimensions of 300 mm x 300 mm, and in the sample of Example 5.5, the sound insulation part has dimensions of 500 mm x 500 mm. With these dimensions of the sound insulation part, the dimensions of the sound absorbing material body are adjusted so that the ratio _S2 / _S1 is 0.5. The sample of Comparative Example 5 is the sample of Example 5.1 without the sound insulation part.

Fig. 36 shows a graph of the normal incidence sound absorption coefficient of each sample (samples of Comparative Example 5 and Examples 5.1 to 5.5) obtained by Numerical Analysis 3. From Fig. 36, it can be seen that, when the ratio _S2 / _S1 is constant, the frequency band where the sound absorption effect is obtained shifts to the lower frequency side as the dimensions of the sound insulation part and the sound absorbing material body become larger. The reason for this is that, as already mentioned, in a general sound absorbing material, when its thickness coincides with 1/4 of the wavelength of the incident sound wave, the sound absorption coefficient becomes high, and in the sound absorbing material of the present invention in which a sound insulation part is arranged on the surface of the sound absorbing material body, the diffraction phenomenon occurring at the edge of the sound insulation part lengthens the path length of the incident sound wave inside the sound absorbing material body (the apparent thickness of the sound absorbing material body becomes larger), shifting the frequency band where the sound absorption coefficient becomes high to the lower frequency side, but when the dimensions of the sound insulation part become larger, the diffraction distance becomes longer and the apparent thickness of the sound absorbing material body becomes larger.

2.7 Experiment 4
Finally, experiment 4 was conducted to confirm the sound absorbing effect when a nonwoven fabric film was arranged as a sound absorbing covering material on the surface of the sound insulating part opposite to the sound absorbing material body. Figure 37 is a perspective view showing the samples (samples of Comparative Example 6 and Examples 6.1 and 6.2) used in experiment 4. The sample of Example 6.1 is a sample in which a circular sound insulating part with a diameter of 80 mm is provided at the center of one side of a sound absorbing material body made of a urethane foam in a disk shape with a thickness of 20 mm. The sample of Example 6.2 is a sample in which the upper side of the sound insulating part in the sample of Example 6.1 (the surface of the sound insulating part opposite to the sound absorbing material body) is covered with a sound absorbing covering material made of a nonwoven fabric film (meltblown nonwoven fabric). The sample of Comparative Example 6 is a sample in which the sound insulating part has been removed from the sample of Example 6.1.

Figure 38 shows a graph of the normal incidence sound absorption coefficient of each sample (samples of Comparative Example 6 and Examples 6.1 and 6.2) measured in Experiment 4. From Figure 38, it can be seen that the sample of Example 6.2, which has a sound-absorbing covering material made of a nonwoven fabric membrane, has a better sound absorption coefficient from the low frequency side than the sample of Example 6.1, which does not have a sound-absorbing covering material made of a nonwoven fabric membrane. From this, it was found that in order to obtain a better sound absorption coefficient from the lower frequency side, it is effective to cover the sound-insulating part with a sound-absorbing covering material made of a nonwoven fabric membrane.

REFERENCE SIGNS LIST 10 Sound absorbing material 11 Sound absorbing material body 11a Sound absorbing material 11b Sound absorbing material 11c Sound absorbing material 12 Sound insulating part 13 Sound absorbing covering material 14 Air layer 20 Wall 50 Incident sound wave α ₁ Surface (sound insulating part arrangement surface)
_α2 surface

Claims (8)

A plurality of non-air-permeable sound-insulating parts that diffract sound waves incident on the sound-absorbing body are repeatedly arranged on at least one surface of the air-permeable sound-absorbing body in the vertical and horizontal directions of the surface with gaps of 5 mm or more between each other,
The sound-absorbing body is formed of a porous material having a flow resistance of ¹⁰⁷ N·s/m4 or ^less ,
The sound-insulating portion is formed of rubber, resin, or metal having a flow resistance of 10 ⁸ N·s/m ⁴ or more;
A sound-absorbing material characterized in that a ratio _S2 / _S1 of a total area _S2 of sound-insulating parts arranged on the surface to an area _S1 of the surface of the sound-absorbing material body is set to 0.1 or more and less than 0.99, thereby preventing Helmholtz resonance from occurring.
2. The sound-absorbing material according to claim 1, wherein the surface density of the sound-insulating portion is 0.01 kg/ ^m2 or more.
3. The sound absorbing material according to claim 1, wherein the sound insulating portion is a patch-like member attached to the surface of the sound absorbing body.
3. The sound absorbing material according to claim 1, wherein the sound insulating portion is formed by a paint-based material applied to the surface of the sound absorbing body.
3. The sound absorbing material according to claim 1, wherein the sound insulating portion is a molten film portion formed on the surface of the sound absorbing body.
6. The sound absorbing material according to claim 1, wherein the surface of the sound insulating portion opposite to the sound absorbing body is covered with a breathable sound absorbing covering material.
A polymerized sound absorbing material in which a plurality of sound absorbing materials according to any one of claims 1 to 6 are stacked in the thickness direction.
The polymerized sound absorbing material of claim 7, in which the sound insulating portion of one layer of sound absorbing material and the sound insulating portion of another layer of sound absorbing material arranged above the first layer are arranged so as not to overlap in the thickness direction.