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

TECHNICAL FIELD [0001] The present invention relates to a porous sound absorbing structure which reduces sound from a noise emitting source. BACKGROUND ART [0002] 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 each other through an air layer, and thereby a Helmholtz resonance principle is utilized to perform noise control. When the Helmholtz resonance principle is utilized, for example, a relationship of a general formula f=(c / 2π)×∫{β / (t+1.6φ)d} holds, where f is a resonance frequency, c is sound velocity, β is an aperture ratio, t is a plate thickness of the inside plate, φ is a diameter of the through hole, and d is an air layer thickness. Air in the portion of the through hole is drastically vibrated to the so...

AI Technical Summary

Benefits of technology

[0007] According to the porous sound absorbing structure according to the present invention, the aperture ratio of the second outside member exceeds 3%, which promotes the conversion of the air vibration into the heat energy by the viscous effect of the through hole in the inside member, and the sufficient sound absorbing performance can be exerted in the wide frequency band. Additionally, because the aperture ratio of the second outside member becomes not more than 50%, the rigidity of the second outside member can be secured to some extent.

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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