A. C. C. Warnock
J. D. Quirt
R. E. Halliwell
J. A. Birta
Acoust. Group, Inst. for Res. in Construction, Natl. Res. Council Canada, M27, Montreal Rd., Ottawa, ON K1A 0R6, Canada
Sound absorbing material placed in the cavity of a hollow wall reduces the transmission of sound through the wall. The influence of density of commonly used materials, such as glass fiber, has been the subject of some argument. Also, it is sometimes thought that the position of the sound absorbing material in the cavity is important. The work to be presented is part of a large series of measurements studying sound transmission through double panel walls. Several types of glass fiber and mineral wool were placed in the cavity formed between two sheets of 3-mm-thick Lexan. Densities ranged from 10 to 145 kg/m[sup 3] and airflow resistivity ranged from 5 to 50 krayl/m. For the materials studied, the influence of material type on sound transmission class (STC) was small: only one or two points. The influence on transmission loss varied with frequency. Largest effects on transmission loss (changes of about 8 dB) were seen at the frequencies around 1000 Hz. The thickness and position of the materials were varied. Highest transmission loss was obtained when the sound absorbing material covered the entire inner surface area of the specimen. The same volume of material filling the cavity width but only partially covering the inner surface area, filling the lower half for example, gave lower transmission loss values.