Measuring acoustic impedance: The results of a worldwide round robin

Abstract

ASTM Committee E-33 on Environmental Acoustics has published two different test methods for determining the normal incidence acoustic impedance and sound absorption coefficients of materials using an impedance tube. Method C-384 involves the use of the traditional standing-wave apparatus using pure tones. Method E-1050 involves the use of a two-microphone technique that provides improved measurement speed and increased detail in the performance versus frequency spectrum. Committee E-33 organized a round robin test program in order to generate ASTM required precision and bias statements for both test methods. Although not required by ASTM, the program also provided an excellent opportunity to compare the results obtained by the two measurement methods. Twenty-two laboratories expressed initial interest and fourteen laboratories from five countries throughout the world eventually participated in the program utilizing either one or both of the test methods. This paper discusses the organization of the program, the test results that were reported, and the conclusions that were drawn from a statistical analysis of the reported test results.