AFMG Network Forum

intercessor · Member

Hi again,
I was using Ray Tracing w/ Impacts to get RT times on a couple different projects. What I keep coming up with is the Schroeder calculations keep coming up with extremely low times compared with Eyring and Sabine. I am talking about 3 to 4 seconds less. I have a couple questions, first what may I have configured wrong to come up with such a disparity and second, are probe calculations more accurate than using Local Decay Time in the mapping module? I have to add that on one of the projects I did a 20 order, 500k+ rays per speaker calculation.

Good day

Stefan · Member

Hi,

first please note, that neither Raytracing Impacts nor Local Decay Time can take into account scattering factors. This is only possible when using the AURA module for EASE. Additionally, because the number of particles/rays is limited all raytracing methods suffer a decrease of detection density towards greater times (because the detection probability decreases the longer the particle is on its way).

In AURA this is compensated for, but in Raytracing Impacts you would have to use one of the tail generation functions to estimate the reverberant tail and add missing pulses. Unfortunately this procedure is not always straight-forward and should be used with care. Without the tail the energy density at the end of the simulated response is often too low and may lead to low RTs accordingly.

So if you are really interested in performing room-acoustic analysis you will have to look at AURA or other room-acoustic tools.

Regarding particle numbers, also here the "resolution rule" applies. You need to increase the number/resolution until nothing changes anymore. It is always recommendable for random-process based calculations to check a second run with identical parameters to get an idea of the errors involved.

Stefan