JP5008277B2 - Sound absorbing structure and sound absorbing material using fine perforated plates - Google Patents

Description

  The present invention relates to a sound absorbing structure and a sound absorbing material using a fine perforated plate, and particularly to a sound absorbing structure and a sound absorbing material using a fine perforated plate which is a resonator type sound absorbing material.

  Conventionally, sound-absorbing structures have been widely used for the purpose of adjusting the sound environment such as noise countermeasures and improvement of acoustic characteristics in architectural spaces (hereinafter referred to as sound fields) where sounds such as concert halls, gymnasiums, and meeting halls exist. Yes. As shown in FIG. 7, generally used sound absorbing structures include (A) a porous sound absorbing structure, (B) a plate (or membrane) vibration type sound absorbing structure, and (C) a resonator type. It can be classified into three types of sound absorbing structures (see Non-Patent Document 1). The performance of the sound absorbing structure can be expressed as a sound absorption rate (= 1- (intensity of reflected sound Ir / intensity of incident sound Ii)) for each sound frequency.

  The porous sound absorbing structure shown in FIG. 7 (A1) has a sound absorbing material 20a made of minerals or plant fibers such as glass wool, rock wool, cotton, cloth, etc. having a large number of complexly connected gaps (hereinafter referred to as open cells) inside. It is the sound absorption structure used as. When sound enters the open cell, a part of sound energy is consumed and absorbed by friction with the peripheral wall of the open cell, viscous resistance, vibration of the material fibrils, and the like. The sound absorption characteristic (frequency characteristic of sound absorption rate) of the porous sound absorption structure is generally small in the low sound range and large in the high sound range as shown in the graph of FIG. If the porous sound-absorbing material 20a is thickened, the sound absorption coefficient in the mid-low range increases, but the weight also increases. For this reason, as in Patent Document 1, a lightweight sound-absorbing panel in which a cloth made of glass fiber or nylon fiber, which is a porous sound-absorbing material 20a, is attached so as to cover the front and back surfaces of the breathable honeycomb core material has been proposed. Yes.

  The plate (or membrane) vibration type sound absorbing structure shown in FIG. 7 (B1) is a sound absorbing structure using a non-breathable airtight plate such as a thin plywood plate or canvas or an airtight film as the sound absorbing material 20b. An airtight plate or film placed on the wall or ceiling of the sound field via a back air layer constitutes a mass-spring vibration system using the plate or film as a mass and the elasticity of the back air layer as a spring, and its resonance frequency. When the sound is incident, it vibrates well, and its internal friction consumes sound energy and absorbs the sound. The sound absorption characteristic of the plate (or membrane) vibration type sound absorption structure generally shows a peak in the low sound range (about 200 to 1000 Hz) as shown in the graph of FIG. 2 (B2), but the sound absorption coefficient is not so large.

  The resonator type sound absorbing structure shown in FIG. 7 (C1) is a sound absorbing structure using a resonator having a cavity (for example, a Helmholtz resonator) as the sound absorbing material 20c. An example of the resonator-type sound absorbing material 20c is a perforated plate in which independent through holes having a diameter of several to several tens of mm are formed in gypsum board or plywood, or a diameter of 0.1 as disclosed in Patent Documents 2 and 3. It is a perforated panel (hereinafter referred to as MPP or micro perforated plate) in which a large number of independent fine through holes of about 1 mm are formed. A perforated plate placed on the wall or ceiling of the sound field via a back air layer uses the air in the through hole (corresponding to the hole in Fig. 7 (C1)) as the mass, and the back air layer (in the cavity of the figure) A mass-spring vibration system with a spring of elasticity), and when the sound of the resonance frequency (resonance frequency) is incident, the air in the fine through-hole vibrates vigorously, and the sound energy is consumed by friction with the surroundings. Sound absorption. The sound absorption characteristic of the resonator type sound absorption structure shows a very large sound absorption rate at the resonance frequency as shown in the graph of FIG.

  In the actual sound absorbing structure of the sound field, the above-described three types of sound absorbing materials 20a, 20b, and 20c are used alone or in combination depending on the required sound environment. For example, by inserting glass wool, rock wool, etc., which is a porous sound absorbing material 20a, into the air layer behind a perforated gypsum board with a diameter of several to several tens of millimeters, which is the resonator type sound absorbing material 20c, a wide frequency band (hereinafter referred to as “bandwidth”) In some cases, the sound absorption structure can provide a high sound absorption coefficient.

Junichi Maekawa et al. “Architecture and Environmental Acoustics” Kyoritsu Publishing Co., Ltd., September 2000, 2nd edition, pp. 74-81 Japanese Industrial Standard "Acoustics-Measurement of sound absorption coefficient and impedance with impedance tube-Standing wave ratio method" JIS-A-1405 Japanese Industrial Standard "Measurement method of sound absorption coefficient of reverberation room method" JIS-A-1409 JP 2002-227323 A Japanese National Patent Publication No. 9-502490 JP-T 8-510020 Publication JP 2004-076462 A JP 2001-295448 A

  Of the resonator-type sound absorbing material 20c described above, the fine perforated plate can select the sound absorption characteristics by adjusting the thickness of the plate, the diameter and pitch of the through holes, the thickness of the air layer behind, and the like. It has the advantage that water resistance / durability can be improved by selecting. However, since the sound absorption bandwidth is relatively narrow and the sound absorption rate is not sufficient with a fine perforated plate alone, it may be difficult to adjust the sound environment. As mentioned above, it is possible to combine it with the porous sound absorbing material 20a such as glass wool, but the glass wool etc. has a risk of condensation accident, low durability, other than sound absorbing characteristics such as influence on the human body due to dust etc. Problems have been pointed out, and glass wool or the like may not be used depending on the usage conditions in the sound field. If the sound absorption rate of the fine perforated plate can be increased and the sound absorption bandwidth can be widened, it can be expected that the sound absorbing plate can be used in a sound field under various usage conditions without using glass wool or the like.

  Therefore, an object of the present invention is to provide a sound absorbing structure and a sound absorbing material that can obtain a high sound absorption coefficient by using a fine perforated plate.

Generally, the sound absorption rate of the sound absorbing material varies depending on the incident condition of the sound wave. As shown in FIG. 8A, the sound absorption coefficient when a plane sound wave enters the sound absorbing material 20 perpendicularly (incident angle θ = 0 degree) is called a normal incident sound absorption coefficient α ₀ . Further, as shown in FIG. 5B, the sound absorption coefficient when the sound wave enters the normal line of the sound absorbing material 20 at the incident angle θ (> 0) is called the oblique incident sound absorption coefficient α _θ . In the actual sound field, sound waves with various incident angles θ exist as shown in FIG. 3C, and the sound absorption rate when sound waves are randomly incident from all directions (incidence angles of 0 to 78 degrees). Is called the sound field incident sound absorption coefficient α, and is obtained by spatially integrating the normal incident sound absorption coefficient α ₀ and the oblique incident sound absorption coefficient α _θ as shown in equation (1).

For example, as shown in FIG. 6A, the normal incident sound absorption coefficient α ₀ is obtained by inserting a sound absorbing plate 20 into one end of an acoustic tube 21 having a diameter w smaller than the sound wavelength λ, and generating sound waves (plane waves) from the other end to the sound absorbing plate 20. Can be measured by vertical incidence (see Non-Patent Document 2). The sound field incident sound absorption coefficient α is set such that a sound absorbing plate 20 having a predetermined area s is placed in a reverberation chamber 27 having a predetermined volume V and surface area S as shown in FIG. Can be measured (see Non-Patent Document 3). Although measurement of the oblique incidence sound absorption coefficient alpha _theta is rather difficult, a number of measurement methods have been proposed (see Non-Patent Document 1).

FIG. 9 shows the oblique incident sound absorption coefficient α ₃₆ , α ₄₈ , α _{60 for} the normal incident sound absorption coefficient α ₀ and the incident angle θ of 36 degrees, 48 degrees, 60 degrees and 72 degrees obtained by theoretical calculation. , Α ₇₂ , and a graph of the sound field incident sound absorption coefficient α obtained by integrating (adding) them. As can be seen from the figure, in the fine perforated plate 1, the normal incident sound absorption coefficient α ₀ is the largest, and the oblique incident sound absorption coefficient α _θ gradually decreases as the incident angle θ increases. For this reason, the sound field incident sound absorption coefficient α of the fine perforated plate 1 obtained by integrating them has a narrow sound absorption bandwidth and becomes lower overall. If the decrease in the oblique incident sound absorption coefficient α _θ depending on the incident angle θ can be improved, the sound field incident sound absorption coefficient α of the fine perforated plate 1 should be improved. The present invention has been completed as a result of research and development based on this idea.

1 and 3A, the sound absorbing structure using the micro perforated plate according to the present invention has a micro perforated plate 1 in which through holes 3 are formed at a required pitch and the surface is exposed to a sound field. Is opposite to the wall 15 or ceiling 16 in the sound field via an air layer 17 , and the wavelength λ of the upper limit frequency of the sound to be absorbed from the sound field by the partition wall 7 orthogonal to the fine perforated plate 1 is opposed to the air layer 17. The direction of sound wave propagation on the back surface side of the perforated plate 1 is provided with a honeycomb-shaped formed body 5 that is smaller and larger than the required pitch of the through holes 3 and is divided into a plurality of cylindrical voids 6 separated from the back surface of the perforated plate 1. Is controlled in a direction orthogonal to the perforated plate 1.

Further, referring to the embodiment of FIG. 1A, the sound absorbing material using the fine perforated plate according to the present invention is formed on the back surface of the fine perforated plate 1 in which the through holes 3 are formed at a required pitch and the surface faces the sound field. The honeycomb is partitioned into a plurality of cylindrical voids 6 having a diameter w smaller than the wavelength λ of the upper limit frequency of the sound to be absorbed from the sound field and larger than the required pitch of the through holes 3 by the partition wall 7 orthogonal to the fine perforated plate 1. The shaped molded body 5 is provided away from the back surface of the perforated plate 1 and the sound wave propagation direction on the back surface side of the perforated plate 1 is controlled in a direction orthogonal to the perforated plate 1.

The cross-sectional shape of each cylindrical space | gap 6 can be made into circular, a square, or a polygon, as shown in FIG.1 and FIG.2. Also as shown in FIG. 3, it is Rukoto provided a honeycomb-shaped molded body 5 which is divided into a plurality of cylindrical cavities 6 only in the vicinity portion of the microperforated plate 1 of the air layer 17. Preferably, the diameter w of each cylindrical gap 6 of the honeycomb formed body 5 is set to 0.6 times or less the wavelength λ of the incident sound from the sound field. More preferably, as shown in FIG. 1 and FIG. 3 (B), an airtight diaphragm or membrane 9 (hereinafter referred to as “both”) is arranged on the side opposite to the finely perforated plate 1 of each cylindrical void 6 of the honeycomb formed body 5. A hermetic vibration film 9).

  The sound absorbing structure and sound absorbing material using the micro perforated plate according to the present invention includes a plurality of apertures w having a diameter w smaller than the wavelength of the incident sound from the sound field by the partition wall 7 orthogonal to the micro perforated plate 1 in the air layer 17 behind the micro perforated plate 1. Since it divides into the cylindrical space | gap 6, there exists the following remarkable effect.

(A) By partitioning the back air layer 17 into the cylindrical gap 6 having a diameter w smaller than the wavelength of the incident sound, the back air layer 17 of the sound incident on the fine perforated plate 1 from an oblique direction (incidence angle θ> 0) Can be controlled to be perpendicular to the fine perforated plate 1 (incident angle θ = 0).
(B) By propagating incident sound in the back air layer 17 in the direction perpendicular to the fine perforated plate 1 regardless of the incident angle θ, the air (mass) in the through hole of the fine perforated plate 1 and the elasticity of the back air layer ( The mass-spring vibration system formed by the spring) can be vibrated in the direction perpendicular to the fine perforated plate 1 to suppress a decrease in the oblique incident sound absorption coefficient α _θ depending on the incident angle θ.
(C) By suppressing the decrease in the oblique incident sound absorption coefficient α _θ depending on the incident angle θ, the sound absorption band α of the sound field incident sound absorption coefficient α, which is an integral value thereof, is widened, and the sound field incident sound absorption coefficient α is improved. Can do.
(D) By providing the airtight vibration membrane 9 on the opposite side of each cylindrical gap 6 from the fine perforated plate 1, the sound absorption bandwidth of the sound field incident sound absorption coefficient α due to the synergistic effect of the cylindrical gap 6 and the airtight vibration film 9. And the sound field incident sound absorption coefficient α can be further improved.

  FIG. 1 shows an embodiment of a sound absorbing plate 10 of the present invention using a fine perforated plate 1 and a honeycomb formed body 5. The fine perforated plate 1 in the illustrated example is a panel 2 having a required thickness in which a large number of fine through holes 3 having a diameter of about 0.1 to 1 mm are formed at a required pitch as described above, and if the through holes 3 can be accurately drilled. There is no restriction | limiting in particular of a material, For example, they can be made from glass, metal, wood, plastic, plasterboard, etc. The thickness of the fine perforated plate 1, the diameter and pitch of the through holes 3, and the thickness of the back air layer can be appropriately selected according to the sound environment that requires sound absorption adjustment. The sound absorption in the fine perforated plate 1 is dominated by the resonance phenomenon caused by the mass-spring vibration system formed by the air (mass) in the through-hole 3 and the elasticity (spring) of the back air layer 17, so that the panel 2 itself The vibration and rigidity of the are irrelevant. Therefore, it is possible to form the fine perforated plate 1 using the sheet-like panel 2.

  The honeycomb-shaped formed body 5 in the illustrated example is formed so as to form a plurality of cylindrical voids 6 partitioned from each other by partition walls 7 orthogonal to the fine perforated plate 1. In the illustrated example, the flat partition walls 7 are combined in a lattice shape to form a honeycomb-shaped formed body 5, and the cross-sectional shape of each cylindrical void 6 is rectangular. However, the cross-sectional shape of the cylindrical gap 6 is not limited to a square as long as the diameter w is smaller than the wavelength of the incident sound, as will be described later. For example, as shown in FIGS. 2A and 2B, a plurality of cylindrical partition walls 7a and 7b having a circular or polygonal cross-section are closely adjacent to each other to form a honeycomb-shaped formed body 5, and the cross-sectional shape is circular. Or it can be set as the polygonal cylindrical space | gap 6a, 6b. Further, as shown in FIG. 3C, the corrugated plate-like partition wall 7c and the plate-like partition wall 7d are arranged in parallel with each other to form a honeycomb-shaped formed body 5 having a cylindrical gap 6c having a triangular cross-sectional shape. .

  As shown in FIG. 1 (A), a honeycomb formed body 5 is superposed on one surface of a fine perforated plate 1 to form a sound absorbing plate 10 of the present invention. By superposing the honeycomb formed bodies 5, the air layer 17 behind the fine perforated plate 1 can be partitioned into a plurality of cylindrical gaps 6 orthogonal to the fine perforated plate 1. The through hole 3 of the fine perforated plate 1 and the cylindrical gap 6 of the honeycomb formed body 5 do not need to correspond to 1: 1, and the diameter w of the cylindrical gap 6 can be made larger than the pitch of the through holes 3. . The fine perforated plate 1 and the honeycomb formed body 5 are preferably brought into contact with each other or bonded together. However, if the back air layer 17 can be partitioned into a plurality of cylindrical gaps 6, they may be provided somewhat apart from each other without being brought into contact with each other. For example, as shown in FIG. 3 (A), the surface of the fine perforated plate 1 faces the sound field and the back surface is opposed to the ceiling 16 or the wall 15 in the sound field via the back air layer 17 so as to face the back air layer 17. The honeycomb formed body 5 is inserted in a direction in which the partition walls 7 are orthogonal to the fine perforated plate 1. The partition wall 7 of the honeycomb formed body 5 need only be airtight so that the back air layer 17 can be partitioned into a plurality of cylindrical gaps 6, and does not aim at increasing the rigidity of the fine perforated plate 1. There are no particular restrictions. Although the same material as the fine perforated plate 1 can be used, the weight can be reduced by using paper, fiber reinforced plastic, or polycarbonate.

  The diameter w of each cylindrical gap 6 of the honeycomb formed body 5 is made smaller than the wavelength λ of the incident sound from the sound field, preferably 0.6 times or less of the wavelength λ of the incident sound. For example, in order to propagate the measurement target sound wave in parallel with the tube axis in the acoustic tube 21 of FIG. 6, if the acoustic tube 21 is a square tube, its diameter w is 0.5 times or less the wavelength λ of the measurement target sound wave (0.5λ ≧ w). It is known that if the acoustic tube 21 is a circular tube, its diameter w is 0.58 or less (0.58λ ≧ w) of the wavelength λ of the sound wave to be measured (see Non-Patent Document 2). As can be seen from this, if the cross-sectional shape of each cylindrical gap 6 of the honeycomb formed body 5 is square or circular, the diameter w is 0.6 times or less (0.6λ ≧ w) of the wavelength λ of the incident sound. Thus, the sound wave incident in the cylindrical gap 6 can be propagated in parallel to the central axis, that is, in the direction orthogonal to the fine perforated plate 1. Preferably, the aperture w is 0.5 times or less (0.5λ ≧ w) of the wavelength λ of the incident sound. Even if the cross-sectional shape of the cylindrical gap 6 is other than a square or a circle, the propagation direction of the incident sound is made parallel to the central axis by selecting the diameter w within a range smaller than the wavelength λ of the incident sound. Or close to parallel.

That is, if the air layer 17 behind the fine perforated plate 1 is partitioned into the cylindrical gap 6 having a diameter w smaller than the wavelength λ of the incident sound by the honeycomb formed body 5, the propagation direction of the incident sound in the back air layer 17 is finely perforated. It can be controlled in a direction perpendicular to the plate 1. As described above with reference to FIG. 9, the sound absorption coefficient α _θ of the fine perforated plate 1 decreases as the incident angle θ of the incident sound increases. One cause of the decrease in the sound absorption coefficient α _θ is the background air due to the incident angle θ. It is thought that the propagation characteristics in the layer 17 change. If the incident sound is propagated in the back air layer 17 in the direction orthogonal to the fine perforated plate 1, the mass-spring vibration system of the fine perforated plate 1 is vibrated in the direction perpendicular to the fine perforated plate 1, so The incident sound can be expected to have the same sound absorption rate as that of the normal incident sound (incident angle θ = 0). If the oblique incident sound absorption coefficient α _θ of the fine perforated plate 1 can be increased to the same level as the normal incident sound absorption coefficient α ₀ , it is possible to improve the sound field incident sound absorption coefficient α and increase the bandwidth.

  The upper limit of the frequency of sound that needs to be adjusted in a general sound field is about 4000 Hz, and its wavelength is about 8.3 cm (= 33200 cm / 4000 Hz), so that the sound absorbing material 10 of the present invention has such a range. In order to improve the sound field incident sound absorption coefficient α, for example, the diameter w of each cylindrical gap 6 of the honeycomb formed body 5 is about 5 cm (≈8.3 × 0.6) or less, preferably about 4 cm (≈8.3 × 0.5) or less. do it. It is also possible to provide the honeycomb shaped body 5 in the entire back air layer 17 between the fine perforated plate 1 and the sound field wall 15 and ceiling 16, but as shown in FIG. If only the vicinity of the fine perforated plate 1 in the back air layer 17 is partitioned into a plurality of cylindrical gaps 6, the sound field incident sound absorption coefficient α can be sufficiently increased (see Experimental Example 1 described later). Accordingly, the thickness d of each tubular void 6 of the honeycomb-shaped formed body 5 (the length d between the openings at both ends of the tubular void 6) can be made thinner than the thickness D of the back air layer 17 ( (See also FIG. 1B).

[Experimental Example 1]
In order to confirm the sound absorption characteristics of the sound absorbing structure in which the fine perforated plate 1 and the honeycomb-shaped molded body 5 are superposed, the sound absorbing plate 10 of the present invention is made as a prototype, and the sound field is incident using the reverberation chamber 27 of FIG. An experiment was conducted to measure the sound absorption coefficient α. In this experiment, a thickness d in which through holes 3 having a hole diameter of 0.5 mm were drilled at a pitch of 5 mm and a metal micro-perforated plate 1 having a thickness of 0.5 mm and a plurality of cylindrical gaps 6 having a diameter w = 8 mm were formed. A sound-absorbing plate 10 was prepared using a honeycomb-shaped molded body 5 (paper honeycomb panel) of 5 cm. The aperture ratio of the through hole 3 of the fine perforated plate 1 is 0.64%. As shown in FIG. 3A, the fine perforated plate 1 is suspended on the entire surface of the ceiling 16 of the reverberation chamber 27 via an air layer 17 having a thickness D = 30 cm to form a double ceiling, and the surface of the fine perforated plate 1 The sound-absorbing material 10 of the present invention was obtained by inserting the honeycomb-shaped formed body 5 on the back surface of the fine perforated plate 1. The volume of the reverberation chamber 27 is 54 m ³ , the surface area of the ceiling 16 is 20 m ² , and the volume of the back air layer 17 is 6 m ³ . A test sound wave enters the sound absorbing material 10 on the ceiling from the speaker 22 in the reverberation chamber 27 at every frequency from all directions, and the reverberation sound in the reverberation chamber 27 is transmitted from the microphone 25 to the real-time analyzer 26 to receive the sound field incident sound absorption coefficient α. Was measured. For comparison, the sound field incident sound absorption coefficient α of the fine perforated plate 1 without the honeycomb-shaped formed body 5 was also measured.

  The experimental results are shown in the graph of FIG. The dotted line graph of FIG. 3 shows the sound field incident sound absorption coefficient α of only the fine perforated plate 1, and the solid line graph shows the sound field incident sound absorption coefficient α of the fine perforated plate 1 on which the honeycomb shaped bodies 5 are superimposed. As can be seen from the comparison of both graphs, by dividing the back air layer 17 into a plurality of cylindrical gaps 6 by the honeycomb-shaped formed body 5 in a wide band of 200 to 2000 Hz as compared with the case of only the fine perforated plate 1. The sound field incident sound absorption coefficient α of the perforated plate 1 could be increased. That is, it was confirmed that the sound absorbing plate 10 of the present invention can broaden the sound absorption. Further, the sound field incident sound absorption coefficient α can be improved only by providing the honeycomb formed body 5 having a thickness d = 5 cm with respect to the thickness D = 30 cm of the back air layer 17. It was confirmed that the sound field incident sound absorption coefficient α of the fine perforated plate 1 can be improved only by dividing about / 6 into the cylindrical gap 6. In this experimental result, the peak sound absorption coefficient of the solid line graph is slightly lower than the peak sound absorption coefficient of the dotted line graph. However, the thickness d of the honeycomb formed body 5 is adjusted, or the honeycomb formed body is described later. It is possible to further improve the sound absorption coefficient of the solid line graph by providing the hermetic vibration film 9 on the opposite side of the micro-perforated plate 1 of each cylindrical gap 6.

  Thus, it was possible to achieve the object of the present invention, “a sound absorbing structure and a sound absorbing material that can obtain a high sound absorption coefficient using a fine perforated plate”.

  In the embodiment of FIG. 1, a non-breathable gas-tight vibrating membrane 9 is provided in an opening (sound exit opening) on the opposite side of the micro-perforated plate 1 of each cylindrical void 6 of the honeycomb-shaped formed body 5. The sound field incident sound absorption coefficient α of the fine perforated plate 1 is further increased by a synergistic effect of the airtight vibration film 9 and the airtight vibration film 9. An example of the airtight vibrating membrane 9 is made of, for example, paper or a thin polyfilm, and has a thickness that allows the impedance of the vibrating membrane 9 to be negligible compared to the impedance of air. As shown in FIG. 1 (A), a finely perforated plate 1 and an airtight vibration film 9 are superposed on one surface and the opposite surface of a honeycomb-shaped formed body 5 to form a sound absorbing plate 10 of the present invention. The hermetic vibration film is desirably brought into contact or bonded so as to close the outlet opening of the honeycomb-shaped formed body 5, but may be provided somewhat apart without contacting both.

[Experiment 2]
In order to confirm the sound absorption characteristics of the sound absorbing structure in which the fine perforated plate 1, the honeycomb-shaped molded body 5 and the airtight vibrating membrane 9 are superposed, the same fine perforated plate 1 and the honeycomb-shaped molded body 5 as those in Experimental Example 1 are used. An experiment was conducted to measure the sound field incident sound absorption coefficient α using the reverberation chamber 27 of (B). In this experiment, as shown in FIG. 3 (B), a paper-made hermetic vibration film 9 is bonded to the opposite side of the micro-perforated plate 1 of the honeycomb-shaped formed body 5 of Experimental Example 1, and then the micro-perforated plate 1 It was inserted into the air layer 17 behind and used for the experiment.

The experimental results are shown in the graph of FIG. The dotted line graph in FIG. 3 shows the sound field incident sound absorption coefficient α of only the fine perforated plate 1, and the solid line graph shows the sound field incident sound absorption coefficient α of the fine perforated plate 1 in which the honeycomb formed body 5 and the airtight vibration film 9 are superimposed. As can be seen from the comparison of both graphs, the honeycomb formed body 5 divides the back air layer 17 into a plurality of cylindrical gaps 6 and provides an airtight vibration film 9 at the outlet opening of each cylindrical gap 6 in the experiment. The sound field incident sound absorption coefficient α of the fine perforated plate 1 could be increased in almost the entire band of 20 to 4000 Hz used. In other words, it is confirmed that the sound field incident sound absorption coefficient α of the fine perforated plate 1 can be remarkably improved and the bandwidth can be broadened by superimposing the honeycomb-shaped molded bodies 5 whose outlets are blocked by the airtight vibrating membrane 9. did it. The details of the effect of improving the sound field incident sound absorption coefficient α by the airtight vibration film 9 are unknown, but the resonator type sound absorption structure in FIG. 7 (C1) and the plate (membrane) vibration type sound absorption structure in FIG. This is considered to be partly due to the cooperative sound absorption effect due to the combination.

  The sound absorbing plate 10 of the present invention can be obtained by simply superposing a relatively thin honeycomb-shaped formed body 5 and an airtight vibration film 9 on the air layer 17 behind the fine perforated plate 1, as shown in FIG. The incident sound absorption coefficient α can be significantly improved. It has not been known so far that the sound field incident sound absorption coefficient α of the fine perforated plate 1 can be improved with such a simple configuration, and the use range of the fine perforated plate 1 can be expected to be greatly expanded by the sound absorbing structure of the present invention. . For example, not only the sound field wall 15 and ceiling 17 but also interior materials and panel materials 18 such as partitions installed in the sound field (see FIG. 1 (B)) via a back gap 17 (thickness D-d). By making the sound-absorbing material 10 of the present invention face each other, the sound-absorbing material 10 of the present invention can be used as a sound-absorbing interior material or a sound-absorbing partition for adjusting the sound environment.

These are explanatory drawings of the Example of the sound-absorbing material of this invention. These are explanatory drawings of an example of the honeycomb-shaped molded object used by this invention. These are explanatory drawings of the sound absorption structure of this invention applied to the ceiling of a sound field. These are graphs which show the sound field incident sound absorption coefficient of the sound absorption structure of FIG. These are graphs which show the sound field incidence sound absorption coefficient of the sound absorption structure of FIG. 3 (B). These are explanatory drawings of the experimental apparatus which measures the sound field incident sound absorption coefficient of a sound absorption structure. These are explanatory drawings of each sound absorption structure of a porous type, a plate (or film) vibration type, and a resonator type, and their sound absorption characteristics (sound absorption rate). These are explanatory drawings of incident conditions of sound waves. These are explanatory drawings of the sound field incident sound absorption coefficient by the conventional resonator type sound absorption structure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Fine perforated board 2 ... Panel 3 ... Fine through-hole 5 ... Honeycomb-shaped molded object 6 ... Cylindrical space | gap 7 ... Partition 9 ... Diaphragm or film | membrane 10 ... Sound absorbing material
14 ... Rigid plate 15 ... Wall
16 ... Ceiling 17 ... Back air layer
18 ... Panel material
20a ... Porous type sound absorbing material
20b… Plate (membrane) vibration type sound absorbing material
20c ... Resonator type sound absorbing material
21 ... Acoustic tube 22 ... Speaker
23 ... Noise generator 25 ... Microphone
26 Real-time analyzer
27 ... Reverberation room

Claims (7)

A through-hole is drilled at a required pitch, and the back surface of the fine perforated plate with the surface facing the sound field is opposed to the wall or ceiling in the sound field via an air layer , and the partition perpendicular to the perforated plate is placed on the air layer By providing a honeycomb-shaped molded body partitioned into a plurality of cylindrical voids having a diameter smaller than the upper limit frequency wavelength of the sound to be absorbed from the sound field and larger than the required pitch, away from the back surface of the perforated plate, A sound-absorbing structure using a fine perforated plate, in which the sound wave propagation direction on the side is controlled in a direction perpendicular to the perforated plate. 2. The sound absorbing structure according to claim 1, wherein a honeycomb-shaped formed body partitioned into the plurality of cylindrical voids is provided in a portion of the air layer in the vicinity of the micro-perforated plate. 3. The sound absorbing structure according to claim 2, wherein an airtight diaphragm or a membrane is provided on the opposite side of each cylindrical void of the honeycomb-shaped formed body from the finely perforated plate. The sound absorbing structure according to any one of claims 1 to 3, wherein a diameter of each cylindrical gap of the honeycomb formed body is 0.6 times or less of a wavelength of incident sound from a sound field. The required pitch is smaller than the wavelength of the upper limit frequency of the sound to be absorbed from the sound field by the partition perpendicular to the perforated plate on the back surface of the fine perforated plate having through holes drilled at the required pitch and facing the surface to the sound field. Utilizing a fine perforated plate in which a honeycomb-shaped formed body partitioned into a plurality of cylindrical voids with larger diameters is provided away from the back side of the perforated plate and the sound wave propagation direction on the back side of the perforated plate is controlled in a direction orthogonal to the perforated plate Sound absorbing material. 6. The sound absorbing material according to claim 5 , wherein an airtight vibration plate or a film is provided on the opposite side of each of the cylindrical voids of the honeycomb-shaped formed body to the micro perforated plate. The sound-absorbing material according to claim 5 or 6 , wherein the diameter of each cylindrical void of the honeycomb-shaped formed body is 0.6 times or less the wavelength of incident sound from the sound field.