AFMG Network Forum

firatozgenel · Member

I work on a really simple model to understand how it works. The room is rectangular with dimensions 10*10*5 with source position (-2,3-1.5) and receiver position(2,7.5,1.5)(room is symmetric at x-axis). Speaker is a point source with 98dB SPL at 1m and finally absorption coefficient of the material used in the room is set to 0,1 0,5 and 0,9 for three cases. When I run the room with mirror imaging and open the impact file in Probe, clarity values are -2,7 for 0.1 abs coef
12,7 for 0.5 abs coef and
46,7 for 0.9 abs coef.
However, when I compare these results with the ones that I derive with the calculations or with other software there is a big difference. Am I missing something? What are the possible reasons for other acoustical analysis software and EASE giving completely different result?
Best Regards
Fırat

Jim Mobley · Member

Mirror Image is specifically for the study of early reflections, first, second or third order typically. The Clarity Ratios are ratios of energy before and after a specific time, 7, 50 and 80 milliseconds. For Clarity Ratio calculations, you should use Ray Tracing, Find Impacts, set the time to equal the Sabine or Eyring RT, don't limit the order and set the number of rays to get an Impact Chance of at least 50%. More is better of course, but this will likely be millions of rays, so calculation time becomes an issue.

This calculation is better and much faster done in AURA if you have the AURA module.

firatozgenel · Member

Hi Jim,
Thanks for your reply. I've tried what you said but after calculating for 17mins I got the message no local impacts. For 2.18 s Reverberation time (Sabine's) I used nearly 18000000 rays to get 50% impact chance. I accept the calculation time but why did I got the message? (By the way, I do not have Aura module) Thanks for yout concern.
Best regards

Jim Mobley · Member

Without seeing your model, I really can't guess. If you can, please pack and send it to me and I'll look at it.