The application of EN 12354-1 to lightweight construction materials requires that theresonant component of the sound reduction index be separated from the reduction indexmeasured according to ISO 140-3 or ISO 15186-1 which also includes contributions fromthe non-resonant component. One method of separating the resonant component is tocalculate the non-resonant sound reduction index and then subtract it from the total,measured value. In this investigation, the non-resonant component was calculated usingdifferent theories and subtracted from the total sound reduction index measured for a steelpanel. However, almost all of the resulting resonant sound reduction indices were negativeover much of the frequency range. The errors in the separation of the components mayhave been due in part to measurement uncertainty which may be larger than the differencebetween the non-resonant and total sound reduction index below the critical frequency. Abetter method of separation may be a correction factor which is applied to the measureddata. However, the correction factor itself must not be prone to errors or it mayunderestimate the resonant component of the sound reduction index.
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