On the use of the integrated impulse response method for laboratory reverberation measurements

  • Bodlund K
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Abstract

Reverberation measurements can be made both by means of the integrated impulse response method and the traditional interrupted noise method utilizing a short time mean square pressure averaging. The former method, originated by M. R. Schroeder, yields highly reproducible decay curves which are free of the random fluctuations that characterize the traditional method as a result of the noise excitation. From a literature survey of the integrated impulse response method it appears that to data analog techniques have been mostly used in the implementation of this method. However, the application of digital techniques appears to offer several advantages in comparison with analog techniques. To fill this gap the potential means of applying digital techniques is analyzed. Suitable recommendations are made as to the time sampling interval, the quantization and the qualification of data samples, and the determination of the decay curve. In connection with the time sampling interval it is shown that undersampling can be successfully applied to limit the number of samples involved, especially at high frequencies. A digital measurement procedure designed according to these principles, utilizing a wave form recorder and a mini computer, is outlined and is shown to work efficiently in various situations. Comparisons have been made with results obtained by using more traditional methods, showing good agreement. When a reverberant chamber was finally chosen as an example for application, the important observation was made that although the individual spatial sample curves were often rather irregular and bent, especially at low frequencies, the spatial ensemble average decay curves were relatively straight lines, except for the initial portion of the decay. This fact merits further attention and should significantly facilitate the interpretation of reverberation measurements made to identify the typical decay rate of the decaying sound energy in a room. © 1978.

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Authors

  • K. Bodlund

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