Porous sound absorbing structure

Abstract

A porous sound absorbing structure 10 includes an exterior plate 1 and a closing plate 2 in order to suppress a decrease in sound absorbing performance in a wide frequency band. An interior plate 3 is arranged between the exterior plate 1 and the closing plate 2, and air layers 4 and 5 are located between the exterior plate 1 and the interior plate 3 and between the interior plate 3 and the closing plate 2 respectively. The exterior plate 1, the interior plate 3, and the closing plate 2 are arranged while opposed to each other. Many through holes 1a and 3a are made in the exterior plate 1 and the closing plate 2 respectively. In the interior plate 3, a plate thickness t2 and a diameter φ2 and an aperture ratio β2 are set so as to generate an viscous effect in air passing through the through hole 3a. The aperture ratio β1 of the through hole 1a in the exterior plate 1 is set more than 3% and not more than 50%.

Description

CROSS-REFERENCES TO RELATED APPLICATIONS[0001]This application is a Divisional application of U.S. application Ser. No. 11 / 578,666 filed Oct. 17, 2006, which is a national stage application of PCT / JP05 / 7322 filed Apr. 15, 2005. Priority is claimed based on U.S. application Ser. No. 11 / 578,666 filed Oct. 17, 2006, which claims priority to PCT / JP05 / 7322 filed Apr. 15, 2005, which claims priority to Japanese Patent Application No. 2004-135145 filed on Apr. 30, 2004, all of which is incorporated herein by reference.TECHNICAL FIELD[0002]The present invention relates to a porous sound absorbing structure which reduces sound from a noise emitting source.BACKGROUND ART[0003]Recently, a porous soundproof structure is becoming operational in various fields. In the porous soundproof structure, a plate member in which a hole is not made and a plate member in which many through holes are made over a surface are arranged on an outside and an inside with respect to a sound source while opposed to ...

AI Technical Summary

Benefits of technology

The present invention is related to a porous sound absorbing structure that can effectively absorb sound in a wide frequency range. The structure consists of two outside members with many through holes, and the inside member has many more through holes. The size and shape of the through holes in the inside member are designed to create a viscous effect in the air passing through, while the through holes in the outside members are larger and have a specific aperture ratio to ensure sufficient sound absorbing performance. The second outside member is located on the opposite side of the first outside member with respect to the inside member, and its aperture ratio is set between 3% and 50% to ensure both sufficient sound absorbing performance and rigidity. The technical effect of this structure is that it can effectively absorb a wide range of frequencies, while also providing sufficient rigidity to the outside members.

Problems solved by technology

However, when the Helmholtz resonance principle is used, there is a problem that a soundproof effect is exerted only to the sound having the particular resonance frequency while the soundproof effect is extremely lowered to the sounds having frequencies except for the resonance frequency.

However, in the porous soundproof structure, the interior plate is exposed on a sound source side, and the diameter of the through hole is extremely small, so that sometimes clogging is generated in the through hole.

Furthermore, sometimes the diameter of the through hole cannot be decreased due to constraints from other functions (drainage, painting, and the like).

Thus, because the size of the through hole diameter is subject to the restraint, there is a problem that the frequency band in which the sound absorbing performance can be exerted becomes narrowed.

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