Federica Morandi

Extraction of the envelope from impulse responses using pre-processed energy detection for early decay estimation

The Schroeders backward integration method and its applications have been widely studied in the literature; some papers analyze the performance of the method, some others suggest various enhancement techniques. In spite of these findings, there exist several cases where the energy decay curve extracted using the classical backward integration method and the parameters computed from it seem not always representative of the phenomenon under study. Among them, the cases where the early decay is dependent on strong, distinct reflections occurring just after the direct wave, as in most Italian opera houses. Other cases are measured impulse responses with a very low signal-to-noise ratio or missing the direct wave. In the literature, alternatives to the Schroeders method have been proposed, ranging from Hilbert transform to non-linear processing techniques. In this work a method for the extraction of the envelope based on pre-processed energy detection for early decay estimation is proposed. It is shown that it returns an envelope well matching the first part of the decay even in non-linear cases, returning detailed information on the first part of the decay. The performance of the proposed method is presented and discussed for some exemplary impulse responses measured in historical opera houses. A preliminary study on the perceptive relevance of the method is finally presented.

Experimental measurements of flanking transmission in CLT structures

This paper discusses the results of an experimental campaign that led to the characterization of flanking transmission in CLT structures with different connection systems. The vibration reduction indices Kij were measured in accordance with the ISO 10848-1 standard in order to provide data suitable to calculate the apparent reduction index according to the EN 12354-1 standard. The research explored several vertical and horizontal junctions on which different number and the type of screws and plates, different CLT panels, and resilient materials at the wall-floor junction were tested. The results show that the Kij along different transmission paths have a specific trends in frequency that depend on the fastening system and the mutual connection of the panels. Moreover, the analysis shows great discrepancies among measurements performed on CLT panels provided by different manufacturers. The results call for a deeper investigation concerning the mechanical/acoustical characterization of the panels.

Sound energy distribution in Italian opera houses

A typical Italian opera house is a complex system of coupled volumes: fly tower, orchestra pit, cavea (the volume where the stalls are), boxes, loggione (gallery). The way of propagation of the sound energy between one volume and the others is still a subject of research. The present work gives a contribution to the discussion by applying the Barron’s revised theory to the analysis of recent measurements done in several Italian theatres. The averaged values of sound strength versus the distance from the sound source is plotted inserting in the Barron’s equation either the classical reverberation time or the early decay time and different volume values. The significance of the different choices and their agreement with the experimental values are discussed. It is concluded that the spatial distribution of sound strength depends on the sound source position.