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Sound Power Level
Sound power level assessment can be performed using laboratory measurements, or even in situ measurements for engineering class measurements (taking into account the fact that some pieces of equipment are way too big to enter a laboratory!). Those measurements are performed using sound pressure level measurements either in a reverberant room or on an enveloping surface around the sound source of interest using the ISO 3740 series , or using sound intensity measurements according to the ISO 9614 series [76, 77].
Measurement and Computation
Why bother to measure when one can compute? To start with, there will probably be a bit of a difference between the predicted result using simple formulas whose validity domain usually calls for homogeneous materials, and the actual specimen, due to (nonexhaustive list) nonhomogeneities of the materials, imperfect mounting conditions, and even noncompliance of the product with its commercial description. While a computation probably will help to restrict the choices that had been left opened (e.g., regarding mounting conditions and choice of materials) by comparing specimens, ultimately a measurement will be needed to ascertain the actual absolute value (even taking into account some limitations induced by the laboratory conditions). More to the point, one will be able to show the test to the client, bearing in mind that as the saying goes, “Nobody believes a calculation except the person who did it, and everybody believes an experiment or measurement except the person who did it.” Incidentally, this is as good a time as ever to make sure that the contractor will be able to perform the required task and the manufacturer will be able to provide the required technical assistance. For difficult projects, there probably will be a laboratory test to physically validate the solution, and later a proof room construction to enable the architect and the end user to see the result. (Note: When properly built, it will also enable the acoustician to perform measurements on some elements that may have been subjected to limited laboratory tests, e.g., the fagade, due to larger dimensions than those acceptable in the laboratory.) Ultimately, a head of series will be constructed in the actual building under construction; measurements will help validate its implementation by the contractor under real conditions (better discover at this stage that the operating procedure is wrong than after a hundred such constructions have been completed!).
Note: It is extremely tempting for the end user and the contractor to save time and money on such niceties as airproofing. Should that be the case, a valuable test opportunity will be lost.
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