An inexpensive apparatus for testing sound transmission loss in undergraduate labs

A lab for undergraduate students on the transmission of sound through solids offers convenient avenues to teach students about dynamic signals, signal processing, and the complex physics of sound and sound transmission loss (STL). But sound transmission testing is prohibitively expensive, and normally requires either large dedicated spaces or expensive instrumentation. This paper describes an inexpensive lab process for efficiently measuring STL through common construction materials using a lab-built apparatus. Standard STL assessments are heavily dependent on testing details such as microphone and speaker placement, the size and attachment methods of sample materials, and methods of data processing to mitigate data noise caused by resonance, sample boundary conditions, and near-field sound. The process described here deliberately addresses these potential sources of error when measuring sound in a small space, and uses a set of innovative testing and processing approaches to replicate the results of a more rigorous testing procedure. The obtained results match published data and analytical results for STL through simple construction materials sufficiently to be useful for an undergraduate lab, with average deviations from published results and analytical predictions ranging from 1.4–6.5 dB for 5 validation tests.