A Monte-Carlo investigation of the uncertainty of acoustic decay measurements

Measurement of acoustic decays can be problematic at low frequencies: short decays cannot be evaluated accurately. Several effects influencing the evaluation will be reviewed in this paper. As new contribution, the measurement uncertainty due to one-third octave band pass filters will be analysed, taking into account the influence of the magnitude response and the phase distortion.

It will be shown how the error not only depends on the filter but also on the modal density and the position of the resonances of the system under test within the frequency band. A Monte-Carlo computer simulation has been be set up: the model function is a model of the acoustic decays, where the modal density, the resonances of the system, and the amplitude and phase of the normal modes may be considered as random variables.

Once the random input variables and the model function are defined, the uncertainty of acoustic decay measurements can be estimated. Different filters will be analysed: linear phase FIR and IIR filters both in their direct and time-reversed versions. © European Acoustics Association.