SOUND ABSORPTION COEFFICIENT OF PERFORATED PLYWOOD: AN EXPERIMENTAL CASE STUDY Francesco Negro 1 , Corrado Cremonini 1 , Milena Properzi 2 , Roberto Zanuttini 1 ABSTRACT: For sound control in closed spaces, perforated wood-based panels are widely used as walls and ceilings covering for their sound absorption properties in the low frequency range. Despite the high interest in this products, accurate estimation models of their properties are still unavailable. This paper reports the sound absorption properties determined for drilled okoumé plywood intended for interiors covering. The drilling percentage was fixed at 1.5, while different cavity sizes were arranged behind the specimens to evaluate their influence on the sound absorption. Tests were performed by means of the impedance tube method. The experimental data obtained can be used for the development of new estimation models with increased accuracy. KEYWORDS: sound absorption, perforated panels, plywood 1 INTRODUCTION 1234 Sound absorption in enclosures constitutes a relevant topic for many building applications, in particular with respect to large scale structures like public buildings, offices, shopping centres or dining spaces. Such environments, in fact, are often characterized by high noise levels, especially when crowded. Depending on the building typology, many sources contribute to increase the overall noise: people’s voice (Fig. 1), movements, air-conditioning systems etc. Poor acoustics of enclosed spaces can deeply rebound on their usability, particularly with respect to the speech intelligibility. To mention some example, high levels of noise in classrooms make students prematurely tired getting worse the efficiency of learning [2]; speech communication between diners in college halls is recognized to be generally poor [3], while the quality of communication in food courts of shopping centres is strongly affected by ambient noise [4]; finally, poor acoustics in offices can affect the working quality and cause increased stress to workers [1]. Focusing on offices, a recent study performed by Jensen and Arens [5] indicated that acoustic discomfort is perceived by workers as a critical issue in these environments. 1 Francesco Negro, AGROSELVITER Dept., University of Torino, Via Leonardo da Vinci 44, 10095 Grugliasco, Italy. Email: francesco.negro@unito.it 1 Corrado Cremonini, Email: corrado.cremonini@unito.it 2 Milena Properzi, BFH-AHB, Bernerfachhochschule, Solothurnstrasse 102, Postfach, CH-2500 Biel 6, Switzerland. Email: milena.properzi@bfh.ch 1 Roberto Zanuttini, Email: roberto.zanuttini@unito.it Figure 1: Average spectra of normal male (thick line) and female (thin line) speech (from [1]) That study consisted in a survey performed on over 23.000 occupant of office workstations, which rated nine factors of their environment (acoustic comfort, thermal comfort, air quality, lightning, cleanliness etc.). The collected answers pointed out that acoustic comfort reaches the lowest satisfaction score among the different categories. In particular, satisfaction with noise level and speech privacy turned out to be both problematic. On the whole, the above mentioned situations evidence how acoustic control plays a fundamental role. Solutions for acoustic improvement are particularly important for noise emitted in the low frequency range, i.e. below 1600 Hz (Fig. 2).