An additional configuration to standard ASTM E2611-09 for measuring the normal incidence sound transmission loss in a modified impedance tube

Olivier Doutres (1) , Raymond Panneton (1) , Yacoubou Salissou (2)

1 GAUS - Groupe d'Acoustique de l'Université de Sherbrooke
2 LCMA-GAUS - Laboratoire de Caractérisation des matériaux acoustiques-Groupe d'acoustique

This paper presents a three-microphone two-load (3M2L) method for measuring the normal incidence sound transmission loss of a noise control system or material in a modified impedance tube. In the standard ASTM E2611-09, the downstream section of the impedance tube includes two microphones flush with the interior surface of the tube and the proposed four-microphone two-load (4M2L) method to assess the normal incidence sound transmission loss requires the use of two arbitrary acoustic terminations. The method presented here is conceptually identical but (i) the downstream section is reduced to a simple movable rigid backing with one microphone flush mounted on it and (ii) the two arbitrary acoustic terminations are replaced by two air cavities. It thus requires one microphone less and fewer transfer functions. The standard switching technique used to correct the variations between microphones is validated on a symmetrical air layer. The proposed 3M2L method is then applied to a non-symmetrical non-homogenous specimen and validated compared to the standard 4M2L method.

Mots clés: Impedance tube; transmission loss; noise control; sound absorbing material

Domaines: Acoustique [physics.class-ph]

Olivier Doutres, Raymond Panneton, Yacoubou Salissou. An additional configuration to standard ASTM E2611-09 for measuring the normal incidence sound transmission loss in a modified impedance tube. Acoustics 2012, Apr 2012, Nantes, France. ⟨hal-00810671⟩