Bandpass filters for the evaluation of short reverberation times

Abstract

In building acoustics, evaluating the sound insulation of building elements suffers from rather bad reproducibility. The reason is the energy flow between the building element and the surrounding structure of the test laboratory. To get more reproducible measurements, it is desirable to measure the loss factor of the element, e.g., by evaluation of the reverberation time of the structure. Unfortunately, the evaluation of decreasing reverberation times T60 of building elements, for instance in one third octave bands is distorted by a growing influence of the applied bandpass filter. In literature a minimum permissible product of the bandwidth and the reverberation time of the filter B⋅T=16 can be found but no error in the estimation of T60 beyond this limit is given. A maximum admittable error depending on the B⋅T product is derived for several filters used in real time analyzers. An optimized filter according to the IEC 1260 standard is developed and results of simulated and measured short reverberation time evaluations are presented. Other possibilities of the investigation of the loss factors and their practical use are discussed.