JPH0333897A - Sound absorber - Google Patents

Abstract

PURPOSE:To enhance the sound absorbing rate in a low frequency region and to allow the use indoors and outdoors without requiring a large installation space by forming many cylindrical spaces to the length and disposition conforming to the two-dimensional disposition of a square residue system. CONSTITUTION:The sound absorber body 1 has the many cylindrical spaces 3 formed of walls 2. The cylindrical spaces 3 are closed at one end and are opened at the other end. The face arrayed with the open ends is a sound absorbing face 4 where the cylindrical spaces of the same sectional area and different lengths are arrayed randomly. The long cylindrical spaces are partly bent and are disposed behind the short cylindrical spaces to reduce the thickness l of the sound absorber 1. Metallic materials and plastic materials are usable as the material of the walls 2 forming the cylindrical spaces 3. The length of the cylindrical spaces 3 is set integer times the certain unit length and the arrangement thereof is determined in accordance with the square residue system. The sound absorber with which the high sound absorbing coefft. is obtd. in the low frequency range without increasing the thickness and which is easily producible, is highly resistant to weather and is effectively usable indoors and outdoors is obtd. in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a sound absorber used for indoor acoustic design, outdoor noise prevention, etc., and particularly to a sound absorber that exhibits a high sound absorption coefficient in a low frequency range.

[Conventional technology]

Various sound-absorbing materials have been used in the past, but all of them exhibit good sound-absorbing coefficients in high frequency ranges.
The sound absorption coefficient was extremely low in the low frequency range of around 125Hz. Therefore, even if conventional sound absorbing materials were used as they were, they were not very effective in absorbing sound in the low frequency range.

Therefore, as sound absorbing structures in the low frequency range, plate vibration type, perforated plate resonance type, porous type with a rear air layer, etc. have been proposed. However, the sound absorption coefficient of the two-plate vibrating type and the perforated temporary type is at most 0.4 (reverberation sound absorption coefficient).
However, the sound absorption coefficient is still low. On the other hand, with the porous type, it is possible to considerably improve the sound absorption coefficient by providing a large rear air layer, but the overall size becomes large (for example, 60 to 100 cm thick), making it impractical. For any type of sound absorption structure, the material must have a large internal loss coefficient for sound waves, and generally plywood,
Hardboard, gypsum board, glass wool, rock wool, etc. are used. However, these materials are difficult to use alone outdoors due to their weather resistance, and are hardly used in hospitals, food factories, etc. due to hygiene reasons (difficult to sterilize and clean).

[Problem to be solved by the invention]

Recently, the problem of environmental noise has been emphasized, and noise countermeasures have been particularly required in the low frequency range, and there has been a desire to develop a sound absorber having a high sound absorption coefficient in the low frequency range.

The present invention was made in view of this situation, and aims to provide a sound absorbing body that has a high sound absorption coefficient in the low frequency range, does not require a large installation space, and can be used indoors or outdoors. purpose.

[Means to solve the problem]

The present inventors have focused on M. RoSchroeder's diffuse reflector theory and have conducted various demonstration tests thereof.
We obtained the knowledge that the structure acts as an interference-type sound absorber in which sound waves with different phases cancel each other in a frequency range outside the design frequency range, and exhibits a particularly high sound absorption effect in the low frequency range.

The present invention was made based on such knowledge, and
Many cylindrical spaces with one end closed and the other end open.

The sound absorber main body is arranged in an array, and the plurality of cylindrical spaces have a plurality of lengths and are randomly arranged, and further, some of the long cylindrical spaces are bent.

The gist of this invention is a sound absorber characterized by being placed behind a short cylindrical space.

[Effect]

In the above structure of the a-absorbing body, the surface in which the opening surfaces of a large number of cylindrical spaces are arranged acts as a sound-absorbing surface, and the sound waves incident on the sound-absorbing surface, especially the sound waves in the low frequency range, are absorbed. This is because the phase of the sound waves that are incident on the sound absorption surface of the sound absorbing body and reflected changes depending on the depth of the cylindrical space at one reflection position, and as a result, sound waves with different phases interfere with each other, and this interference produces a sound absorption effect. considered to be a thing.

Here, the length and arrangement of a large number of cylindrical spaces are determined by the two-dimensional 5+! of the square remainder series. It is preferable to form the groove according to the position, since a good sound absorption effect can be obtained.

This sound absorber has many cylindrical spaces with different lengths, and the longer cylindrical space is partially bent and placed behind the shorter cylindrical space. , the thickness of the sound absorber can be reduced. Therefore, the installation space for the sound absorber becomes smaller.

The sound absorbing body of the present invention basically does not utilize the sound absorbing effect of the material itself that constitutes the sound absorbing body.

As the material forming the cylindrical space, a highly rigid metal material such as a steel plate without internal loss of sound waves can be used, and in this case, there are no weather resistance or hygiene problems.

It can be installed outdoors5 or used in hospitals2 and food factories. However, the material constituting the main body is not limited to a rigid body.

Since the above-mentioned sound absorbing body has a structure in which a large number of cylindrical spaces are opened on the sound absorbing surface, it is easy for dirt, debris, etc. to enter the cylindrical spaces, and cleaning is difficult. Therefore, the end face of the opening may be covered with a thin metal film such as stainless steel foil or aluminum foil, or a thin film such as a plastic sheet.Even if such three-layer coating is applied, the sound absorption effect in the low frequency range will not be affected much. It has been confirmed that there will be no. A sound absorbing body coated with a fi film is easy to clean and hygienic, so it is particularly suitable for noise prevention in hospital operating rooms, food factories, and the like.

Furthermore, instead of a thin film covering the open end surface of the sound absorber body,
Glass wool board, rock wool board, sintered metal board.

It is also possible to arrange a porous plate such as a metal fiber plate.

When this porous plate is arranged, it exhibits a high sound absorption coefficient over all I'1 wave numbers from the low frequency range to the high frequency range, so it is preferable. PVF (borifunated vinyl film) on the outer periphery
When used by covering it with a plastic film such as

This is preferable because it is easy to handle and clean.

〔Example〕

The present invention will be described in detail below with reference to one drawing.

FIG. 1 is a schematic perspective view of an embodiment of the present invention, and FIG. 2 is a plan view thereof. The sound absorber of this embodiment includes a sound absorber main body, which is indicated by reference numeral 1 as a whole, and the sound absorber main body 1 has a large number of cylindrical spaces 3 formed by walls 2. This cylindrical space 3 has one end closed and the other end (upper end in the drawing)
are open, and are arranged so that the open ends are on the same plane. The surface where these open ends are lined up becomes the sound absorbing surface 4.

The cylindrical spaces 3 have the same cross-sectional area but different lengths, and the cylindrical spaces 3 have different lengths arranged randomly (the arrangement will be described later). Furthermore, as shown in Figure 3, a part of the longer cylindrical space is bent and placed behind the shorter cylindrical space, thereby reducing the thickness l of the sound absorber. . Wall 2 forming a cylindrical space 3
As the material, metal materials such as steel plate 8 aluminum, plastic materials, etc. can be used.

The length of the cylindrical space 3 is based on the unit length h and is an integral multiple of this unit length. In this embodiment, the arrangement is determined according to the squared remainder series.

Next, the squared remainder series will be briefly explained. p is an odd prime number.

Let a and p be relatively prime integers. When a quadratic congruence equation (%) has a solution, a is said to be the square remainder modulo p.

As an example, the square remainder sequence for the odd prime number p-7 is as follows.

x” = a (Ilod 7) x=O-0” Mi 0 X = 1 − 1” Mi I
4 → 4” = 2 (16=2x7+2
) x = 5 - 5” Mi 4 (25 = 3 x 7 + soil) x =
6 → 6” :=l (36=5X7+earth) From the above, the square remainder series when the odd prime number p=7 is.

− dimension 0, ], 4. 2. 2. 4. 1. 0.
1. 4. 2. 24.1.・-・becomes. In two dimensions, a 7×7 matrix is repeated, which is not shown in Table 1. Here, the first horizontal row and first vertical column (leftmost column) are the numerical values of the above-mentioned -dimensional array, and the other parts are the sum of the numerical values in the corresponding first row and first column (from 7 (if it is smaller) or the sum (if it is larger than 7) minus a multiple of 7.

Table 1 What is the depth of the cylindrical space 3 in the sound absorber 1 shown in FIG.

It is determined by the two-dimensional array of the square remainder series mentioned above, and the numerical values written at the opening end of the cylindrical space 3 in FIGS. 2 and 3 are the numerical values in Table 1. This number indicates the ratio of the depths of the cylindrical space.1For example, in Figure 3, the depth indicated by the number 5 "2'" is 2h, and the depth indicated by the number "3" is 3h.
, the depth indicated by the numerical value "6" is 6h.

Here, the specific dimensions of the cylindrical space are 5 chroad
Determine the desired sound absorption frequency by referring to the design conditions of the ER diffuser reflector.

It may be determined by considering the desired sound absorption coefficient, installation space, cost, etc. In other words, when designing a 5-chroader diffuse reflector, the maximum length of the cylindrical space is set to about 2 wavelengths per layer at the lower limit of the design frequency (diffuse reflection occurs above this frequency), and the opening side length of the cylindrical space is set to , is designed to be 1/2 or less of the wavelength of the upper design frequency limit (diffuse reflection occurs below this frequency). 9 In the sound absorber of the present invention, the dimensions of the cylindrical space are set to the design frequency range of the diffuse reflector where the frequency to which sound absorption is desired is 5 chroader. It may be determined according to the purpose of use, application, etc. within a range that does not fall within the (diffuse reflection range).

The sound absorbing body l shown in FIGS. 1 to 3 may be manufactured as an integral structure as a whole. However, since it is difficult and expensive to manufacture the whole in one piece, it is preferable to manufacture it by dividing it into multiple parts.In that case, create a block with one or more cylindrical spaces, The blocks may be combined to take over the sound absorbing body 1 shown in FIG. 1, or as shown in FIG.
is made into a 4N structure consisting of la, lb, lc, and ld, and each layer may be fabricated separately and 34 layers may be joined together. When the sound absorber main body l is made into a 4N structure, each layer 1a to ld is the 5th layer. The structure is shown in Figures [a), fbl, tc), and (al).In addition, in Figure 5 (al), the portion indicated by hunting 5 has the length of the cylindrical space 0, so there is no space on the upper surface of the space. In addition, in FIG. 5 fat to fdl, the portion indicated by hatching 6 is the bottom wall.

The sound absorber main body 1 shown in FIGS. 1 and 4 can be used as a sound absorber as it is. That is, a sound absorbing wall can be formed by arranging a large number of sound absorbing body bodies 1 so that their sound absorbing surfaces 4 are the front surfaces.

FIG. 6 shows another embodiment of the invention. In this embodiment, a thin film 7 is disposed on the sound absorbing surface 4 of the sound absorbing body 1 shown in FIG. 1 to cover the open end of the cylindrical space that the sound absorbing body 1 has. As the thin film 7 used here, a thin film made of metal such as stainless steel or aluminum, a plastic sheet, or the like can be used. By arranging the thin film 7 on the sound absorbing surface of the sound absorbing body as in this embodiment, cleaning becomes easy.

FIG. 7 shows still another embodiment of the present invention.

In this embodiment, the sound absorbing surface 4 of the sound absorbing body 1 shown in FIG.
A porous plate 8 is disposed at the top to cover the open end of the cylindrical space formed by the sound absorber l. As the porous plate 8 used here, a glass wool plate, a rock wool plate 5, a sintered metal plate, a metal fiber plate, etc. can be used as is or covered with a plastic film.

Further, instead of the porous board, a perforated board material such as hardboard, gypsum board, plywood, etc. may be used.

A large number of sound absorbers shown in FIGS. 6 and 7 can also be arranged to form a sound absorbing wall.

Next, the results of a sound absorption test conducted using the nine sound absorbers of the present invention will be shown.

Example I Only the sound absorbing body 1 with a four-layer structure shown in FIGS. 4 and 5.

External dimensions: 50 CIIX 5 Q cm : 0.7 opening steel plate example opening The opening end surface of the sound absorber body of Example I was covered with a stainless thin film
(see Figure 6).

Example 2 The open end surface of the sound absorbing body of Example 1 was covered with a glass wool plate (density 32 kg/m', thickness Lolm) (see Figure 7).

Comparative example Single glass wool board of Example M.

The reverberation sound absorption coefficients of the above four types of test specimens were determined according to JIS-A1409. The results are shown in Table 2 and FIG.

As can be seen from Table 2 and FIG.
It shows a high sound absorption coefficient over the years.

Example (2) has a slightly lower sound absorption coefficient than Example (2) in the mid-range, but shows a similarly high sound absorption coefficient in the low-range, so it is sufficiently practical from a sanitary standpoint.

Example (3) shows a high sound absorption coefficient over the entire frequency range. As can be clearly seen when compared with the comparative example, the glass wool board alone exhibits only a low sound absorption coefficient in the low to middle range, but the sound absorber of the present invention significantly improves the sound absorption coefficient in the low range. Therefore, for example, by covering a glass wool board with a plastic thin film such as PVF (polyvinyl fluoride film) and combining it with a sound absorber, it can be used as an excellent sound absorbing device with good weather resistance.

In the above embodiments, the cylindrical space formed in the sound absorbing body l has a square cross section, but the cross section is not limited to a square, but may be any other shape such as a rectangle, a triangle and a circle. Moreover, in the above embodiment, there are many cylindrical spaces.

They were arranged so that their open ends were located on the same plane.

The opening ends do not necessarily need to be located on the same plane, but may be arranged to be shifted in the length direction between the seven cylindrical chambers.

〔Effect of the invention〕

As explained above, the sound absorber of the present invention can be made without increasing the thickness (for example, about 30CJI).

It exhibits a high sound absorption coefficient (for example, approximately 0.9) from the low frequency range to the intermediate frequency range, and is easy to manufacture because metal materials such as steel plates and aluminum plates can be used, and it is also weather resistant. Are better. Furthermore, by using plastic material, it is also possible to reduce the weight. Therefore, the sound absorbing body of the present invention has the effect that it can be used extremely effectively in low frequency sound absorbing structures indoors and outdoors.

Furthermore, a sound absorber in which the opening end surface of the cylindrical space is covered with a thin metal film such as stainless steel foil or aluminum foil, or a thin film such as a plastic sheet is easy to clean and hygienic.
It is particularly suitable for noise prevention in hospital operating rooms, food factories, etc.

In addition, a sound absorber in which a porous material is placed on the open end face of a cylindrical space exhibits a high sound absorption coefficient over all frequencies from low to high frequencies, so it can be used as an extremely excellent sound absorber.

[Brief explanation of drawings]

FIG. 1 is a schematic perspective view 2 showing a sound absorber according to an embodiment of the present invention.
FIG. 2 is a plan view thereof, FIG. 3 is a perspective view taken along the line mm in FIG. (bl, (cl, (d)
is a plan view of each layer constituting the sound absorbing body in FIG. 4, FIGS. 6 and 7 are schematic perspective views of other embodiments of the present invention, and FIG.
The figure is a graph showing the results of measuring the sound absorption effect. 1-Sound absorbing body main body, 2--wall, 3-cylindrical space, 4-sound absorbing surface, 5--wall, 6-bottom wall, 7-thin film, 8--porous plate.

Claims (1)

[Claims] The sound absorbing body has a sound absorbing body formed by arranging a large number of cylindrical spaces that are closed at one end and open at the other end, and the cylindrical spaces have a plurality of lengths and are randomly arranged. A sound absorbing body characterized in that a part of a long cylindrical space is bent and placed behind a short cylindrical space.