# RT60 - is my room really this bad?



## Zeitgeist (Apr 4, 2009)

So, after reading threads recommending .35 - .5 RT60 times, and coming up with .2s based on calculations (1400 cuft), I had a few minutes to play with ETF5 last night.

I know that I need to adjust the levels, and do a sweep rather than white noise to get a more accurate measurement... but is the graph below sane?

Can a 10 wide, 20 long, 7' tall room that's drywall and untreated really have RT60 times this high?


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## bpape (Sep 14, 2006)

Seems a bit high on the top end. Bottom end, depending on how the room is built and what's in it, could easily be 2000ms - 3000 seems like a bit much for a room that size.

Yes - you really probably need a good amount of broadband bass control. 

Personally, I like the display options on REW over ETF5 and like to run the sweep. 

Bryan


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## Zeitgeist (Apr 4, 2009)

Thanks Bryan.

I'll have to play with it some more. I figure it shouldn't be too hard to get a better graph, but I've read that one issue that people tend to have with ETF is trying to figure out if the graphs are sane or not, since it's easy to pick settings that yield inaccurate graphs.

I actually forgot that REW could do RT60, so I should check that out again.


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## Zeitgeist (Apr 4, 2009)

I don't know why, but I always forget just how food REW is!

Now I just need to read up on the graphs a little bit, since I always struggle to interpret them.


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## bpape (Sep 14, 2006)

The waterfall is a nice visual way to see what's happening in REW. You see frequency, time, and intensity all in one nice 3D graph


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## tubamark (Jun 25, 2009)

Zeitgeist said:


> Can a 10 wide, 20 long, 7' tall room that's drywall and untreated really have RT60 times this high?


VERY unlikely.
Perhaps you have some bad flutter echo messing up your measurements? Echo is a completely seperate thing from reverberation. 

Please give more info on your room - flooring, furnishings, etc. To get 3 seconds RT (especially down to 20 Hz as shown) in a small drywall room is nearly impossible; your room would have to be built like the old "echo chambers" that recording studios used to have before electronic reverb existed - all surfaces covered with portland cement and sealed-up airtight.

-- Mark


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## Zeitgeist (Apr 4, 2009)

Lets see....... Walls are all drywall, no treatments right now. A couple framed things w/glass/plexiglass... A hollow core door to the unfinished part of basement... I attached my sketchup artistry to give some idea of dimensions.

There is a large bookshelf on the left long wall...... A couch is the only soft furniture in the room.

I was assuming that it was probably a bad measurement, but actually seeing a measurement of RT60 at all is really eye opening for me.

Floor is berber carpet, ceiling is acoustic ceiling tile..


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## Zeitgeist (Apr 4, 2009)

,.


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## Zeitgeist (Apr 4, 2009)

So, it looks like REW has a very different window by default from ETF.

I changed the window in ETF to be similar to REW and it looks mostly agreeable.
The default settings in ETF 50ms-200ms (I think) yield a very very different result.

It looks like REW yields less than .5s, which I'm not sure if that seems too low now..

Edit: I should probably just look at the waterfall... and stop overanalyziing the results.


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## Zeitgeist (Apr 4, 2009)

This is a pretty cool link:
http://www.sae.edu/reference_material/pages/Reverberation Time Calculator.htm#verbcalc

I came up with calculated values of .2 - .3 seconds, which agrees pretty well with REW.


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## tubamark (Jun 25, 2009)

That's more like it. :yes: With tile ceiling and carpet, RT should be extremely low. All you have to worry about now is early reflections, and bass issues - depending on how rigid those walls are. Having all your subs at the same end almost guarantees a modal resonance related to the length of the room. 

-- Mark


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## bpape (Sep 14, 2006)

Actually, that's still a bit on the funky side. RT60 should be higher at low frequencies and lower as you go higher in frequency.

Bryan


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