ASA 125th Meeting Ottawa 1993 May

2pNS8. A new number-theoretic acoustical concrete masonry unit.

Peter D

RPG Diffusor Systems, Inc., 651-C Commerce Dr., Upper Marlboro, MD 20772

A new number-theoretic structural acoustic concrete masonry unit will be described. These new acoustical building blocks uniformly disperse reflections created by the flat surfaces of conventional absorbing block over a broad range of frequencies, while simultaneously providing extended broadband low-frequency absorption, load-bearing reinforced construction, fire-safety, high transmission loss, economy, and an aesthetic appearance. Random-incidence acoustical testing yielded an NRC of 0.85 for the unpainted block and 0.40 for the painted block, with 100% efficiency at 100 Hz. The STC for painted block was 55. Structural testing for both compressive strength and flexural mid-span deflection were in compliance with ASTM C90-90. A novel cavity design, which provided extended low-frequency absorption will be described. The system consists of three blocks. The A and B blocks facing the noise source each contains a partial quadratic residue sequence and the rear mounting C block forms a structural cavity. The acoustical properties of the system address the needs of all musical facilities, movie theaters, auditoriums, school rehearsal rooms, and noise control applications including highway barriers, airports, power plant transformer substations, etc.