Shroyer Sound Testing
During the summer of 2020, the MSU administration decided to assign several large lecture classes to Shroyer Gym so that a large group could meet while still maintaining 2 meter spacing for COVID mitigation.
Shroyer Gym is an active athletic facility not designed as a classroom. It is a large room with approximately 2,100 m2 floor area, and approximately 13,200 m3 of enclosed volume. Wall surfaces are painted concrete masonry unit (CMU), floor is wooden gymnasium floor, and the ceiling is painted metal decking, so the reverberation time was measured to be several seconds. The reverberation caused very low quality and intelligibility of lecture speech when using the existing public address (PA) system.
A decision was made to reduce the reverberation time by applying a commercial sound absorbing material that is sprayed onto existing surfaces. The material, K-13, is a product of International Cellulose Corporation, and consists of a non-combustible cellulose fiber combined with a glue binder. The entire ceiling was sprayed with the K-13 material to a depth of 1 inch. According to the manufacturer, this results in absorptivity of 0.39 at 125Hz, 0.63 at 250 Hz, 0.96 at 500Hz, and 0.99 at 1kHz. The original ceiling absorptivity was probably about 0.1.
Here is a close-up photo of the K-13 material applied to the ceiling structure.
From a distance, the K-13 material blends into the ordinary appearance of the ceiling, and has good light reflectance.
Audio examples recorded in Shroyer Gym using existing PA system
- Rhyme words BEFORE and AFTER treatment (June 29 vs. Aug. 12)
- Sentences BEFORE and AFTER treatment (June 29 vs. Aug. 12)
Reverberation time measurements:
Before treatment, 125 Hz: 4.1 sec RT; After treatment: 3.3 sec
Before treatment, 250 Hz: 4.1 sec RT; After treatment: 2.2 sec
Before treatment, 500 Hz: 3.3 sec RT; After treatment: 2.2 sec
Before treatment, 1 kHz: 2.9 sec RT; After treatment: 1.9 sec
Students seated in Shroyer Gym for a sociology lecture on first day of class (August 17, 2020).