Transmission Matrices: Introduction and Application

date October 30, 2015
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Friday, October 30, 2015 4:00 p.m. in ETC 4.150

David A. Nelson, INCE Bd. Cert., PE
Nelson Acoustics
Elgin, Texas

Layered systems present both challenge and opportunity in noise control.   The equations for a handful of basic situations are worked out in engineering texts, but the number of situations encountered in practice drives a need for a straightforward method of assessing them.  Transmission matrices simplify the evaluation of structures as diverse as foil-covered absorbers, multi-leaf partitions, lined ducts, side-branch resonators, and chambered mufflers.  We’ll demonstrate the theoretical basis, introduce a handful of basic matrices, and use them to address a real-life noise control problem.  A “spin class” uses bass-saturated dance music to encourage people exercising on stationary bicycles.  The throbbing easily penetrates generic walls between commercial spaces because of the low-frequency partition resonance.  When the developer’s architect helpfully specifies an added wall that doesn’t get the job done, the acoustical consultant dusts off his knowledge of transmission matrices to both explain the failure and to propose a solution.