chapter  13
32 Pages

Measurement uncertainty

ByJens Holger Rindel

The fundamental principles of measurement uncertainty in building acoustics are found in the ISO Guide to the expression of Uncertainty in Measurement (GUM) and in ISO 12999-1 (2014). The sound pressure level in a room varies from one point to another, even in an ideal diffuse sound field. These variations are particularly large when the excitation is a pure tone or narrow band noise like a one-third octave band and, thus, some kind of spatial averaging is necessary in order to get a reasonably accurate measurement result. This chapter presents an overview of the theoretical background and methods for estimation of uncertainty in sound pressure level measurements and reverberation time measurements in a room. Below Schroeder's limiting frequency, the modal overlap index is small (less than 3) and the room modes may be too spread to fill the frequency band that is measured.