COMPACT SOUND ABSORBERS FOR LOW-FREQUENCIES

Absorption of the low frequency components of unwanted noise is difficult and expensive by traditional methods using porous materials because of the thicknesses required. A compact and efficient sound absorbing structure constructed without porous material is designed as a simple resonator comprising a panel perforated with small holes backed by an air space. Its performance is predicted by a theoretical model and is verified experimentally using a new facility designed to measure acoustic properties of materials at low frequencies. The test results show that panel vibration has a strong effect on the acoustic properties of the structure. Edge effects are not serious for a large sample of small thickness. Under controlled conditions, test results show good agreement between the theory and experiment and confirm that the extension of the proposed theory to the low frequency range is possible. The absorbing structure investigated here can be constructed in rugged and durable form to withstand blast forces and weather.