Abstract
This paper describes the investigation and analysis on two materials in which one material is a relatively good sound absorber at low frequency range and another is a relatively good sound absorber at high frequency range, combined together in layers to form a better sound absorber for a wider range of frequencies. The layer combinations of the materials are varied and the values of Sound Absorption Coefficient, α are measured experimentally by using impedance tubes with two microphones transfer function method according to ISO 10534-2 standard. The results obtained are compared in terms of the order of material and the number of layer combinations of materials for each sample. The orders of combinations and number of layers of combinations have significant influence on the sound absorption characteristics. The order of materials has reversed effect on Sound Absorption Coefficient, α as the number of layer combination is increased. Increase in the combination number will make the specimen performed relatively better at a wider frequency range.
Highlights
A sound level in a closed room could be reduced or controlled by the use of sound absorber
Porous absorbers which are the subject of this study are materials with an open pore structure and commonly made of light and porous materials such as sponge, foam, cotton, wool, and asphalt
The acoustic performance of a porous absorber is influenced by its physical properties such as fiber size, airflow resistance, porosity, tortuosity, thickness, density and its position [3]
Summary
A sound level in a closed room could be reduced or controlled by the use of sound absorber. Cavity and membrane type absorbers are found useful for high, middle and low frequency range respectively [1]. The acoustic performance of a porous absorber is influenced by its physical properties such as fiber size, airflow resistance, porosity, tortuosity, thickness, density and its position [3]. The sound absorption coefficient will increase in all frequency range as the thickness of the sample increases [9]. Zainulabidin et al, [11] studied the effect of combining two porous materials in fractions in which one material is a relatively good sound absorber at low frequency range and another is a relatively good sound absorber at high frequency range. Combined materials with balance fractions of materials have relatively result in better sound absorption coefficient values over wider range of frequency. One material is a relatively good sound absorber at low frequency range and another is a relatively good sound absorber at high frequency range, combined together in layers to form a better sound absorber for a wider range of frequencies
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