Experimental and analytical investigation on sound transmission loss of cylindrical shells with absorbing material

Abstract

In this study, sound transmission through a thin-walled cylindrical shell is investigated both analytically and experimentally. A theoretical model based on statistical energy analysis (SEA) is developed in order to calculate the noise reduction and sound transmission loss of the cylindrical shell. The procedure to obtain the parameters involved in the SEA model, such as radiation efficiency and loss factors, is explained in detail. An experimental setup was constructed in a reverberation chamber to evaluate the transmission loss of the cylinder using two experimental methods. First the transmission suite method which includes measurements of the sound pressure levels inside and outside of the cylinder using microphones was used. Then the sound intensity method was used in which the transmitted sound intensity is measured with a sound intensity probe. The experimental results are compared with the analytical results obtained from the SEA theory, which shows good agreement. By comparing both experimental techniques, the transmission suite method is found to have advantages over the other method at low frequencies. However, the sound intensity method is more applicable in the medium and high frequency regions between the ring and critical frequencies in order to predict the noise transmission characteristics of the cylindrical shell. Another experiment was conducted with absorbing materials placed inside the cylinder. The use of sound absorbing material produced a significant reduction in the noise level in the cylinder specifically in the high frequency range. The effects of the absorption coefficient on the acoustical behavior of the cylindrical shell were also investigated theoretically.