On the accuracy of the subtraction method for in-situ reflection and diffusion coefficient measurements.

Graduate Program in Architectural Acoust., Rensselaer Polytechnic Inst., 110 8th St., Troy, NY 12180.
The Journal of the Acoustical Society of America (Impact Factor: 1.5). 03/2010; 127(3):1752. DOI: 10.1121/1.3383680
Source: PubMed


The subtraction method is a technique critical to measuring in-situ reflectionabsorption coefficients as well as diffusion coefficients. In order to isolate a reflection, a reference measurement including only direct sound is subtracted from one with direct sound and the reflection of interest. However, taking two measurements with exactly the same direct sound component is complicated by environmental conditions, such as changes in temperature, air movement, and exact microphone positioning. These variations can cause small time differences between the reference and the measurement which prevent complete subtraction of the direct sound; the residual direct sound then pollutes analysis of the isolated reflection. This work evaluates several methods to compensate for the differences to achieve minimal interference from the residual direct sound. A metric for gauging the success of the subtraction is proposed and the influence of the subtraction effectiveness on variations in the measured diffusion coefficient will also be discussed.

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