Acoustic Properties of Wood-Based and Non-Wood-Based Materials for Piano-Case Making/Akusticna svojstva drvnih i nedrvnih materijala za izradu kucista klavira

This article presents the possibilities of substituting expensive and scarce wood materials in the construction of piano cases, especially the front panels of upright pianos. Three-layer blockboard, multi-layer plywood, medium-density fibreboard (MDF), and Purenit were selected for the study. These materials were long-time climatised at 20 [degrees]C and 50% relative air humidity. Their frequencies, damping coefficient and relative amplitude were measured. The density [rho], sound velocity v, dynamic modulus of elasticity E', sound impedance [Z.sub.n] and Acoustic Conversion Efficiency (ACE) were calculated. With the materials used to make the front panels of an upright piano, a subjective assessment of the instrument's acoustic response was made. The presence of front panels of any type was found to have a negative effect on the sound except at low frequencies. With panels fitted, the best acoustic properties were achieved by blockboard, followed by plywood, MDF and Purenit panels in that order; this was affirmed by the subjective assessment. The best acoustic performance was achieved by blockboard and plywood. Taking both price and performance into consideration, MDF presented the best compromise. Purenit was ruled out due to its high damping properties. KEYWORDS: composites; acoustic; non-destructive-test; piano case U ovom su clanku prikazane mogucnosti zamjene skupih i rijetkih drvenih materijala za izradu kucista klavira, posebice prednjih ploca uspravnih klavira. Za istrazivanje su odabrane stolarska ploca, furnirska ploca, srednje gusta ploca vlaknatica (MDF) i purenit ploca. Ti su materijali dugotrajno klimatizirani pri temperaturi 20 [degrees]C i 50%-tnoj relativnoj vlaznosti zraka. Mjerene su njihove frekvencije, koeficijent prigusenja i relativna amplituda. Izracunane su gustoca [rho], brzina zvuka v, dinamicki modul elasticnosti E', zvucna impedancija [Z.sub.n] i ucinkovitost akusticne pretvorbe (ACE). Napravljena je subjektivna procjena akustickog odziva instrumenta za materijale upotrijebljene za izradu prednjih ploca uspravnog klavira. Utvrdeno je da prednje ploce uspravnih klavira izradene od bilo koje vrste odabranih ploca imaju negativan utjecaj na zvuk, osim na niskim frekvencijama. Prema subjektivnoj procjeni, najbolja akusticna svojstva pokazala je stolarska ploca, zatim furnirska ploca te MDF i purenit ploca. Najbolja akusticna svojstva imaju stolarska i furnirska ploca. Uzimajuci u obzir cijenu i performanse, MDF je najbolji komprom