# Problems with RT 60



## Guest (Jul 9, 2008)

Hi,

first of all thanks for this great software.
I've noticed some strange effect taking place after adding (additional) bass trapping to a room. The Topt RT-60 sometimes showed longer decay times for the lowest band. This happened under various circumstances in various occasions. RT-20 and RT-30 always looked plausible. I also rans comparisons with different measurement software which did not show this effect.
Is there an explanation for this? 
If you need more information, I'd be happy to provide it.

Greets from Germany


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## brucek (Apr 11, 2006)

You'll have to tell us what you mean by "the lowest band"? 

RT60 is somewhat meaningless in the modal region (up to ~ 200Hz). The smaller the room, the higher the frequency that you would ignore. Use waterfall plots at frequencies in the modal range.

brucek


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## JohnM (Apr 11, 2006)

Easiest way to see what is happening would be to use the Impulse Response view, select the octave band filter which is giving the odd results, click "calculate RT60" and select the Schroeder integral and regression line for display, then see what happens to the regression line for the different RT60 measures (Topt, T20, T30). However at the lowest frequencies RT60 measurements are not valid except in very large spaces as the underlying assumptions on which the RT60 calculation is based do not apply.


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