Barometric pressure and acoustic absorption coefficient : Interactions and effect for common absorptive systems

In the area of material testing, a topic of recent study has been the role of barometric pressure on the measured acoustic impedance (and absorption coefficient) of select simple absorbers such as fiberglass. To date all of the research has been conducted using small scale samples in an impedance tube under ASTM test method E1050. Theoretical calculations based on the previous work of Mechel suggest a change in the absorption coefficient (a) from +0.06 to -0.08 in specific frequency bands for fiberglass samples of typical thickness and density. Experimental results have supported these predictions. However, unmodified fiberglass boards or batts constitute only a small fraction of absorptive materials and systems used in architecture and noise control today. This paper will extend the experimental work to include a variety of absorptive approaches including samples that simulate wall panels, office partitions, locally reacting absorbers, and membrane absorbers. In some cases, the impact of barometric pressure is similar to that of fiberglass. In most cases, the effect is small relative to test precision. The relative impact of other important experimental factors such as sample mounting and errors associated with the apparatus will also be discussed.