Modeling a representative room to evaluate sound measurement methods with improved reproducibility for ASTM ISR testing

Abstract

The low-frequency one-third octave bands for the standard ASTM ISR (Impact Sound Rating) are generally non-diffuse for small rooms we usually come across for field testing. This is because of low modal density in low frequencies in small rooms. Because of the non-diffusivity, the Sound Pressure Level (SPL) measured by microphones is controlled by the room modes. This increases the non-reproducibility of the test method. In the current standards, the modal density and the room non-diffusivity are ignored. Recent research shows that it is important to measure in lower frequencies, at least down to 50 Hz one-third octave band to characterize the impact performance of lightweight structures. With these lower frequencies, the non-diffusivity problem will be more pronounced. In our work, we are simulating a representative room and trying out different sound measurement ideas that will not depend on the non-diffusivity of the room, therefore, improving the reproducibility of the test method. This work will be followed up with some testing on real structures in real rooms. An initial study from this work was presented at the ASA 2021 Seattle meeting.