Reverberation room method

Test Methods. Two basic types of test methods are commonly used to measure sound-absorption in test laboratories the reverberation room method and the impedance tube method. 

Test Methodfor Sound Absorption and Sound Absorption Coefficients by the Reverberation Room Method, ASTM C423-90a, ASTM, Philadelphia, Pa., 1990. Standard Practices for Mounting Test Specimens During Sound Absorption Tests, ASTM E795-92, ASTM, Philadelphia, Pa., 1992. 

The transmission coefficient is the fraction of incident energy transmitted through a partition or a textile layer when a sound wave is incident upon it, and the transmission loss is the logarithm of the reciprocal of the transmission coefficient. Two types of transmission loss are commonly measured with a layer of textile material. The random incidence transmission loss is measured in a reverberation room using the reverberant room method, while the normal incidence sound transmission loss is measured in an impedance tube using the transfer matrix method. 

Sometimes, it is necessary to characterize the sound insulation characteristics of materials using a less expensive and less time consuming approach than the reverberant room method, or to have small samples tested when larger samples are impossible to construct or to transport to a laboratory. In these cases, the transfer matrix method can be used to measure the normal incidence sound transmission of the materials or samples. The transfer matrix can be used to determine additional acoustic properties of the material and to allow calculation of acoustic properties of built-up or composite materials by the combination of their individual transfer matrices (ASTM E2611-09,2009). 

ASTM C423-09, 2009. Standard test method for sound absorption and sound absorption coefficients by the reverberation room method. American Society for Testing and Materials. ASTM C522-03, 2009. Standard test method for airflow resistance of acoustical materials. 

McGrory, M., Cirac, D.C., Gaussen, O., Cahrera, D., 2012. Sound absorption coefficient measurement Re-examining the relationship between impedance tube and reverberant room method. In Proceedings of Acoustics 2012—Fremantle, Australia. 

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