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

Authors
Publisher
Canadian Acoustical Association / Association canadienne d'acoustique
Publication Date
Keywords
  • Tubes (Components)
  • 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
Disciplines
  • Musicology
  • Physics

Abstract

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.

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