An Investigation into the Variability of Sound Transmission Loss Tests

In many cases, the results from a sound transmission loss (STL) test can differ from facility to facility. Despite the presence of standardized test specifications such as SAE J1400 [1], many issues can create variations in the data unique to that particular setup. These situations have presented themselves in recent tasks in which a reverberation room was relocated into a smaller area than was previously available. Current test projects in the relocated test facility have shown a need to better understand the details influencing the quality of the test data. Issues such as the sample orientation, the volume of the reverberation room, the quality of the sealing between the reverberation and anechoic rooms and even the material itself or the operator's style of positioning the sample all had to be reconsidered. It was determined that an investigation into causes of these differences needed to be launched to improve the setup of the STL test and provide more reliable data. A gage repeatability and reproducibility approach in SAE J1400 testing will be undertaken to show how these factors, including, but not restricted to microphone position and sample setup, can affect test results within the context of the J1400 standard. This paper is intended to be a record of findings that will ideally serve as a reference which better quantifies the influences that these various factors have on the quality of the test.