Three-Microphone Two-Cavity method for measuring sound transmission loss in a modified impedance tubeCanadian Acoustics, Vol. 39 No.3 (2011)
AbstractThe normal incidence sound transmission loss (nSTL) is an important indicator to assess the sound insulation property of acoustic materials. A literature review of the main methods used to measure the nSTL using a plane wave tubes is given elsewhere by the authors [Salissou and Panneton 2009]. Today, the two most recognized methods are the 4-microphone 2-load (4M2L) and 1-load (4M1L) methods. While the 4M2L method is a general method, the 4M1L method is limited to materials being geometrically symmetric and invokes the reciprocity principle [Allard et al. 1993]. In an attempt to reduce the number of microphones, a method based on two upstream microphones only was proposed [Panneton 2009]. However, when tested experimentally, the method has singularities that are not yet resolved. For symmetrical materials, this difficulty was circumvented by adding a third microphone on the hard termination cap backing the sample [Salissou and Panneton 2010, Doutres et al. 2010]. The resulting three-microphone method was proved to be efficient for characterizing the dynamic properties. In parallel to the present work, Rodriguez et al. [Rodriguez et al. JASA 2011] presented a generalization of the latter three-microphone method (the 3M-TMTC method). However, their appraoch is restricted to samples with flat and symmetrical surfaces as the third microphone is in direct contact with the sample. The present paper describes a general 3-microphone 2-load (3M2L) method which generalizes the three-microphone methods. It may be seen as a particular case of the 4M2L method when the surface impedances of the 2 loads are known.
Publication DateFall October 12, 2011
Citation InformationYacoubou Salissou, Raymond Panneton and Olivier Doutres. "Three-Microphone Two-Cavity method for measuring sound transmission loss in a modified impedance tube" Canadian Acoustics, Vol. 39 No.3 (2011)
Available at: http://works.bepress.com/olivier_doutres/29/