Three-microphone two-cavity method for measuring sound transmission loss in a modified impedance tube

Yacoubou Salissou, Raymond Panneton, Olivier Doutres


The normal incidence sound transmission loss (nSTL) is an important indicator to assess the sound insulation property of acoustic materials. The apparatus consists of a finite length rigid walled impedance tube with circularly shaped and uniform inner cross-section. The tube features a loudspeaker at one end and a movable piston at the other end. The loudspeaker is used to generate a plane wave field in the impedance tube. There are two microphones flush mounted upstream the test sample and one microphone flush mounted on the rigid end. Next, a 20-mm thick step discontinuity seeing as a non-symmetrical sample is tested and compared to the standard 4M2L method and 3M-TMTC method. One can note that similar results are obtained between the 3M2L and 4M2L methods, however 4M2L is noisier compared to 3M2L.


Acoustic impedance; Loudspeakers; Microphones; A-plane; Acoustic materials; Finite length; Impedance tubes; Normal incidence; Sound insulation property; Sound transmission loss; Step discontinuity; Test samples; Two microphones; Two-cavity

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