# Too dead?



## pepar (May 30, 2006)

Can someone give me some advice on what target decay time (or target decay time range) should be for a 21x13x8 room? My sense is that my room is a bit dead. Thanks!


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## bpape (Sep 14, 2006)

It's maybe a bit deader than necessary but not ridiculously so. In a room that size, for multi-channel, I'd likely shoot for around 250ms in the middle for an RT60 - though that's not really an accurate way to do it in a small space. You're down approx 40 after 150ms except below 100Hz.

Bryan


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## glaufman (Nov 25, 2007)

bpape said:


> It's maybe a bit deader than necessary but not ridiculously so. In a room that size, for multi-channel, I'd likely shoot for around 250ms in the middle for an RT60 - though that's not really an accurate way to do it in a small space. You're down approx 40 after 150ms except below 100Hz.
> 
> Bryan


What would be the accurate way?


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## pepar (May 30, 2006)

glaufman said:


> What would be the accurate way?


And is there a way to generate a RT30 with REW?


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## bpape (Sep 14, 2006)

Just estimate based on 30db down from your peak and see where it lines up on the time scale.

Bryan


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## glaufman (Nov 25, 2007)

In the lower right corner of the RT60 window there's a dropdown called "decay measure where you can select T30, but I can't advise you of theimplications. Over my head.


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## pepar (May 30, 2006)

glaufman said:


> In the lower right corner of the RT60 window there's a dropdown called "decay measure where you can select T30, but I can't advise you of theimplications. Over my head.


Well, I'll be. Now what does it mean?


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## glaufman (Nov 25, 2007)

:huh:I dunnno...


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## pepar (May 30, 2006)

Maybe you can tell me why me typing I'll be ***** turns into "I'll be moo?" :dontknow:


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## glaufman (Nov 25, 2007)

You can review our Zero Tolerance Rules here:
http://www.hometheatershack.com/forums/misc.php?do=cfrules


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## pepar (May 30, 2006)

glaufman said:


> You can review our Zero Tolerance Rules here:
> http://www.hometheatershack.com/forums/misc.php?do=cfrules


Got it! Surprised about the "euphemism" status of the word, but I will comply. MOOO! :T


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## glaufman (Nov 25, 2007)

Sounds good!:T


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## laser188139 (Sep 19, 2009)

glaufman said:


> In the lower right corner of the RT60 window there's a dropdown called "decay measure where you can select T30, but I can't advise you of theimplications. Over my head.


I'll take a shot at it. The choices here match the choices available on the Impulse diagram. T20 and T30 calculate the best fit line where the levels drop from -5dB to -25dB and -35dB from the initial value. These are done using linear regression fits. Topt appears to look at several different floors, -25dB, -35dB, ..., and determines of these which gives the best fitting curve and chooses that one. I think the greatest value in having a choice is to try different values and see if the results are stable, a sensitivity test to verify that the choice of algorithm is not biasing the results. 

The help under the Graph Panel for the Impulse Graph has a section titled Impulse Response Decay/Reverberation Time that gives more detail on this. (Don't ask me for details about the Schroeder Integral. That would require some real research.)

Bill


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