Acoustical parameters used for the subjective assessment of musical performance spaces

Abstract

The problem of evaluating the subjective acoustical quality of a performance space through studying the value of measurable acoustical parameters is yet to be fully solved. As a contribution to its solution this paper aims to determine whether any relationships exist between the various acoustic parameters most often considered. The acoustical parameters that are topical for this study are in the number of three. The first of these parameters is the Inter-Aural Cross-Correlation Coefficient (IACC), which is a measure of the diffuseness of the sound field in the room. Then the Early Lateral Energy Fraction (ELEF), or a related measure, the Spaciousness (S), is used for estimating the relative amount of early sound energy reaching the listener from lateral incidence. And lastly the Initial Time Delay Gap (ITDG), which is a temporal factor and an indicator of the rapidity of early echoes for contributing to the early signal build-up at following the direct signal. For the evaluation of these parameters, the impulse response, IR, of the investigated enclosure is necessary. In room acoustical contexts the IR of a room is defined as the response that would be recorded by a microphone in response to a sharp and intense sound signal emitted within the enclosure. For the sake of calculation convenience a medium sized rectangular room is considered in this study and which represents a coarse approximation to a small performance hall. The theoretical model used for evaluating the IR makes a combination of the image sources method for wave reflections at the hard surfaces, and an exact model accounting for the diffraction of waves at the corners of the balconies. Furthermore, and in view of a more realistic determination of, especially the IACC, the phenomenon of sound scattering by the head of the listener is also taken into account. The variation of the value of the acoustic parameters with the position within the room at a constant height position for a presumed listener's ears is then presented in threedimensional plots. Furthermore, psychoacoustical experiments have shown that the early part of the IR is decisive for the subjective assessment of performance spaces, and further, that the low frequency components of a signal have an important contribution to the feeling of spaciousness. Therefore, a low frequency filtering of the early part of the IR was accomplished for the needs of this study. As a completion to this study, an attempt has also been made toward enhancing the existence of some possible correlation between the various parameters investigated herein. As a result, simple relations may in fact be established between these parameters, and the usefulness of these relationships may find applications in subjective room acoustical assessments for instance for estimating one of these parameters, when inaccessible, from knowing the value of any of the two other ones.

Evaluation of Acoustic Features after Refurbishment Works Inside Two Historical Opera Theatres Located in Italy

“…A complete explanation of the spatial distribution, related to the sound energy across space, is herein introduced by the inter-aural cross-correlation (IACC). The IACC is defined in the literature [32] as the measure of the diffuseness of the sound field in a room, contributing to assess the envelopment of sound at the listener position. The lower the value of IACC, the better the sense of envelopment.…”

“…lar, the image-source method (ISM) has been applied in combination with the analysis of EDT and ITDG parameters [31][32][33][34], methods employed for understanding the lateral and vertical reflections at the stalls and balconies areas [35][36][37][38][39][40][41][42][43].…”