Effects of microstructure on acoustical insulation of gypsum boards

This paper focusses on the understanding of microstructural effects related to sound transmission loss and critical frequency of gypsum boards. The determination of the critical frequency, through measurements of the mass per unit area, thickness and Young's modulus, indicates that a microstructure exhibiting large gypsum crystals with prismatic shapes obtained by addition of citric acid, yields a value (for example: ≅ 3700 ± 360 Hz for 1.5 mass% of citric acid additive, board thickness: 14 mm) well beyond the sensitive frequency range of human hearing (350–1500 Hz). Concerning the sound transmission loss, acoustic insulation can be significantly improved by both increasing (i) the mass per unit area of the gypsum board, (ii) the thickness and (iii) the loss factor. A sandwich panel consisting of an assembly of two individual gypsum boards prepared with citric acid combined with a glass wool core of 50 mm in thickness shows very promising insulating performances. This result has been predicted theoretically with a transfer matrix method.