Sound absorbing materials, such as glass wool or foam, have been generally used in noise control applications. However their performances in a low frequency range is poor due to inherently poor absorption characteristics.
In this paper, a system which is composed of a membrane and an air cavity is used, in order to control the low frequency noise. It absorbs noise by transforming the acoustic energy into the kinetic energy. To analyze the low frequency characteristics of a single membrane-cavity system, a plane wave model is derived and the relations between system variables are investigated. As a result, the frequency characteristics of a membrane-cavity system were found. Absorption coefficient has a maximum value at a peak frequency. This frequency is mainly determined by the density of membrane and the depth of cavity. In addition, a membrane-cavity system absorbs the low frequency noise with band around peak frequency. This band is primarily determined by damping effect in the system. Furthermore, a multiple membrane-cavity system is investigated by using the transfer matrix method. To show the usefulness of the proposed model, extensive experiments were done. Results show that a multiple membrane-cavity system can lead to more broad noise reduction in the low frequency range than single one.
