Volume 130, Issue 4, October 2011
Index of content:
- ARCHITECTURAL ACOUSTICS 
Limitations of the equivalence between spatial and ensemble estimators in the case of a single-tone excitation130(2011); http://dx.doi.org/10.1121/1.3626163View Description Hide Description
The ensemble-average value of the mean-square pressure is often assessed by using the spatial-average technique, underlying an equivalence principle between spatial and ensemble estimators. Using the ideal-diffuse-field model, the accuracy of the spatial-average method has been studied theoretically forty years ago in the case of a single-tone excitation. This study is revisited in the present work on the basis of a more realistic description of the sound field accounting for a finite number of plane waves. The analysis of the spatial-average estimator is based on the study of its convergence rate. Using experimental data from practical examples, it is shown that the classical expression underestimates the estimator uncertainty even for frequencies greater than Schroeder’s frequency, and that the number of plane waves may act as lower bound on the spatial-average estimator accuracy. The comparison of the convergence rate with an ensemble-estimator shows that the two statistics cannot be regarded as equivalent in a general case.
A comparison of methods to compute the “effective duration” of the autocorrelation function and an alternative proposal130(2011); http://dx.doi.org/10.1121/1.3624818View Description Hide Description
The “effective duration” of the autocorrelation function (ACF), τ e , is an important factor in architectural and musical acoustics. For a general application, an accurate evaluation of τ e is relevant. This paper is focused to the methods for the extraction of τ e values from the ACF. Various methods have been proposed in literature for the extraction of the τ e from a given signal, but these methods are not unambiguously defined or may not work properly in case of particular signals. Therefore, the general use of these methods may sometimes give rise to questionable results. In the present work, the methods existing in literature for extracting τ e are analyzed, their advantages and drawbacks are summarized, and finally an alternative method is proposed. The proposed algorithm is compared to those found in previous literature, applying them on the same sound signals (classic literature references and other ones publicly available on the Internet). It is shown that the results obtained with the proposed method are consistent with the results of the previous literature; moreover the proposed method may overcome some of the limitations of the existing methods.