Suppression of Sound by Polyurethane Mats in Ventilation Ducts—A Study with a Laboratory Model Setup

Suppression of noise by sound-deadening linings inside ventilation ducts is a complex theoretical problem. Apart from the material constants, such as the coefficients of attenuation and reflection, the geometry of both the duct and the lining must be considered. For these reasons, an easy-to-implement method of measurements can be a desirable practical solution for engineers interested in a comparison of potentially appropriate materials. Vendors of the latter rarely, if ever, provide a customer with full acoustical characteristics of the sound-deadening material. We built a simple model ventilation duct for determining such characteristics rather than just material constants. Apart from the duct itself, only commercial apparatus were used. The duct, however, is simple enough to be built in a mechanical workshop. We tested this setup and determined the sound-deadening characteristics of primary and rebond polyurethane mats. The mats mounted on the inner walls of the duct showed distinct suppression of sound waves of frequencies from 0.7 to 7 kHz. For the third-octave band of 1.6 kHz, the attenuation reached 40 dB. The frequency characteristics of the suppression of sound indeed differed from the respective function of the attenuation coefficient. The original and rebond polyurethane mats similarly suppressed noise.