CATT-Acoustic v9.1

Modeling Module

The hall geometry is described using a structured hierarchic text format created manually, via AutoCAD or other CAD plugins:
Interactive RT estimate calculation:


Included is a very powerful and easy to use spreadsheet-like function where Sabine and Eyring RT estimates can be done while changing absorption. In addition a global ray-tracing can be performed that contiously updates the RT-curve. For some halls (due to a "mixing" shape or suitable diffusion and absorption distribution) the Sabine and Eyring RT estimates come very close to actual T-30 values estimated from line regression on the decay curves. For such halls, what if? RT calculation games can quite safely be based on classical RT estimates. In addition to Undo and Revert options, the surface list can be sorted according to various criteria to aid in understanding which surfaces control the RT most: 1995 prediction round-robin results:
Now more than 25 years later this has to be discussed in a deeper way. At the time I was happy about this type of actually
quite limited verification (one room, but there had previosuly been several internal measurement comparisons) when users
were very uncertain about what GA software could do, and since so many had bad results at the time that worry was real.
The actual text in the paper was:

”Although the accuracy rating is somewhat arbitrary and should not be over-interpreted, it seems to be reasonable ”…
“there are only three programs that are unquestionably reliable in the prediction of room acoustical parameters; F, 8 and 1”.


Unfortunatelly this has many times been totally over-interpreted and assumed to also hold for all other rooms even very non-diffuse,
coupled and even open rooms such as Roman and Greek arena. The  round-robin 1 room was only slightly non-diffuse (T30 slightly
longer than Sabine) and it seems totally forgotten (or for new software users 25 years later not knowing/checking it) that the test
was also only for 1 kHz at a time when one of the three software only had one scattering coefficient (applicable around 500-1k Hz).
Worse, the quote above has even in software PR been "expanded" and claimed to hold for all three round-robin.

In my view the only really meaningful test is for software users to compare their own predictions to measurements and not just once
but continously as new persons come in and start to model. In 2008 there was an official user round-robin (8 users of the same
sofftware) and the results varied enormously.


 
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