The results of a preliminary investigation into the theoretical evaluation and study of the relationship between some room acoustical descriptors used for the subjective assessment of performance halls are considered. The concern is about three parameters, namely, the interaural cross-correlation coefficient (IACC), the early lateral energy fraction (ELEF) or a related measure, the spaciousness S, and the initial time-delay gap (ITDG). To this end, the impulse response (IR) for a hard rectangular room with a side balcony on each lateral wall is calculated. This room configuration is considered a coarse approximation of a small performance hall. The theoretical model used for this calculation represents a combination of the image sources method for the wave reflections at the hard surfaces and an exact model accounting for the diffraction of waves at the wedges of the balconies, the latter being even extended to the second order of multiple diffractions. Furthermore, and in view of a more realistic determination of the IACC, the thus obtained impulse response is convolved with the head-related transfer function (HRTF) for both ears as measured using a dummy head (KEMAR) in an anechoic environment. In this respect the directional characteristics of the different components of the impulse response are accounted for in the IACC, but to a lesser degree than in the ELEF, whereas the ITDG is independent of direction. It is found that simple relations may be established between these parameters, which may be useful for room acoustical assessments or for estimating one of these parameters, when inaccessible, by knowing the value of any of the other ones.
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