Controlled Angle Sound Transmission Loss Experiment 2003-01-1630
This paper reviews how sound transmission loss (STL) of insulators is affected by gravitational and thermal effects. A special STL test fixture was designed and fabricated to quickly and accurately obtain the STL measurement of a sample oriented at various controlled angles. The STL apparatus was designed to roll into a large reverberation chamber and act as the anechoic termination for a two-microphone approach to measuring STL. The fixture was also built with the intention of studying the temperature effects on a material's STL performance.
A variety of samples, including lightweight and traditional barrier decoupled insulators, were tested in the horizontal, vertical, and inverted positions to evaluate gravitational/inertial effects. Thermal effects were investigated by bringing the STL apparatus and sample to a low temperature by moving outdoors, and then rolling the system into the reverberation chamber, at normal room temperature. By making STL measurements at various temperatures as the STL test fixture and test sample system acclimated to an equilibrium temperature of the room, an STL was measured at various temperatures over a wide frequency range.
Test results revealed that the STL test fixture was capable of measuring STL up to 80 dB. There was also good agreement with theoretical predictions, as measured STL values were within 3 dB of analytically modeled predictions between 250 and 6300 Hz. The results of varying sample orientation proved that gravitational effects on STL were insignificant. However, insulation material inertial effects played a significant role in STL performance. Thermal effects on STL were slight.