Evaluation of the crossover frequency based on the analysis of room transfer functions through statistical estimators

• Published in: Applied acoustics 2020-07, Vol.164, p.107247, Article 107247
• Main Authors: Avelar, Marcio, Bonifacio, Paulo, Sant’Ana, Luis, Brandao, Eric, Bertoti, Elvis, Catai, Rodrigo
• Format: Article
• Language: English
• Subjects: Crossover frequency; Modal overlap; Schroeder frequency
• ISSN: 0003-682X; 1872-910X
• DOI: 10.1016/j.apacoust.2020.107247

This paper presents two ways of processing a room’s transfer function with the goal to determine the crossover frequency above which statistical approaches are valid for predicting or evaluating the sound field. One of them uses Kurtosis for analyzing the real and imaginary components of a transfer function. The other one is based on a proper measure developed for the analysis of the phase signal. Both measures are related to the statistical distribution of values within a frequency window. Transfer functions measured in a large reverberation room and in a scale model were analyzed, and provide results for the crossover frequency which are in the expected range. Analytical responses from three shoebox rooms with the same volume and reverberation time on the one hand, and different geometric aspect ratios on the other hand, were also analyzed. Both measures have shown similar and consistent results in these cases, and are sensitive to the aspect ratio from the hypothetical rooms. The effect of increasing sound absorption on experimental and analytical cases were observed, and are also in accordance to the expectation of increasing the modal overlap.