VRIJE UNIVERSITEIT BRUSSEL Acoustics - the Dept. of ...

Chapter 3Measuring sound3.1 Introduction: why measure soundIn order to select a useful measuring technique we need to determine whatthe purpose of the sound measurement is. A first important objective can beto determine a sound pollution problem. To do this extend, measurements ofthe sound pressure level are usually sufficient. In such a case the availabilityof a simple, portable measuring system is desirable. It the hindrance ismomentary, one wishes a swift registration of the peak levels. For a longobservation, an automatic averaging and statistical processing is advised andmost of the times required by the legislator. A second objective can be thereduction of noise after the confirmation of nuisance. One speaks of soundsanitation. Mostly, there is a need to examine the frequency spectrum ofthe sound to accomplish this task. To this extend specific measuring devicesare developed. Measurements in frequency bands gives the general pictureof the composition whereas the linear spectrum can be an important aid inlocalizing the source of the sound. The latter can also be done by usingvector intensity measurements, which will not be discussed in this course.A third objective of sound measurements is to investigate if the norms andregulations concerning noise pollution are not violated. In this case, as weshall see in later modules, the measuring parameters as well as the measuringconditions are often prescribed.3.2 The measurement microphoneA measurement system to measure sound pressure consists of a microphone,signal amplifier, conditionings unit and a measuring device. The microphoneconverts vibrations of the air into mechanical vibrations, these are in turn33