STUDY OF ACOUSTIC TRANSMISSION THROUGH APERTURES IN A WALL

The prediction on sound transmission through an aperture in a wall by using a linear plane wave theory, its corresponding laboratory measurement and the comparison between them are discussed in this paper. In order to identify a frequency range in which the acoustically perfect transmission through an aperture never occurs, the laboratory measurements of transmission loss through three types of aperture of different width ave carried out firstly. A theory of sound field in the aperture by superposing two oppositely propagating plane waves and the transmission loss of the aperture calculated by the theory in the frequency range defined above are described secondly. Finally the comparison of the measured transmission losses with the calculated ones of the apertures is discussed. This paper shows that the acoustically perfect transmission through apertures adopted here happens above 1250 Hz and the locally minimum transmission through an aperture occurs nearly at 200 Hz. The difference between the calculated transmission losses and the measurements is always within 4 decibels. Therefore, the above plane wave theory can be applied to predict the transmission loss of an aperture at frequencies so low that only the plane mode waves propagate in the aperture.