Sound Absorbing Systems Made of Wood cross Sections Paired with Void Cavities - A First Investigation

This study investigates the possibility of exploiting the porous structure of wood for absorbing sound. With this aim, the following system is proposed: 1) the cross section of wood should be exposed to sound waves so that these can activate the vibration of air inside the wood pores; 2) the cross section should be cut to have small thickness to realize a thorough open cell absorber; 3) a void cavity should be left on the back to activate the absorption effect. This setup has been conceived to absorb sound by Helmoltz resonance. To preliminary assess the effectiveness of the system, cross sections of poplar wood were cut 1 mm thick and paired with rear void cavities 15, 30 and 50 mm thick. The normal sound absorption coefficient α was determined through the impedance tube method. Multiple absorption peaks and several α values higher than 0.6-0.7 (αmax=0.99) were measured in the medium-low frequency range. Building on these results, further studies are envisaged to model the acoustic behavior of the system and to set the technical aspects relevant to its feasibility in practice.