Expochirp used to check ReS (Resonant String Shell) - Measurements results B-Format
Once I have evaluated the acoustic parameters for SPL and C80 in each point, I decided to check the spatial coefficients to check if the structure was performing any good in increasing the Apparent Source Width (LFE4) and the spaciousness (BQI, Binaural Quality Index).
To evaluate the latter from a B-Format Impulse Response, I needed to convert this in binaural by using an ambisonic in-phase decoder and HRTF data from the CIPIC library (http://interface.cipic.ucdavis.edu/sound/hrtf.html).
This is not the optimal conversion technique (as demonstrated in this paper http://infoscience.epfl.ch/record/138612/files/2011_Menzer_IEEE%20Trans%20on%20Audio_05456170.pdf?version=2) but it was the one currently easily available to me; it shows errors in the interaural coherence compared to measurements, hence in the evaluation of the coming direction of sound.
From the results we can see that:
- There is not a linear reduction of the lateral efficiency when we go further away from the structure but there is an increase in the last point, most probably due to the side building.
- All LFE4 values stays in the optimal range
- BQI is above the optimal range and is all in the order of 0.9 or more, this is due to the increase of early reflections to the receivers and the absence of reverberant tail that provides more cross correlation between the ears.
- The side building plays an important role in the diversity between left and right ear response.
As an overall analysis, I am quite happy so far for the results achieved.
I have to take into account that this is not a concert hall, where there is a room that provides early an late reflections, and that the optimal ranges mostly do not apply to this project.
It is very difficult to find results for these kind of structures in the literature due to the lack of similar projects.
I am studying more about further improvements and will be posted soon more results, hopefully!!!