# WATERFALL graph , another doubt



## irombeach (Sep 7, 2010)

Hi folks, 
i have another question regarding waterfall graphs.
As written in tons of other posts, waterfall represents "sound decay over time".

So, reading a plot, what are we looking for? 

a) fast decay (vertical downhill from t1...t2...tx)
b) general flatness of the graph?
c) bot of them?


**till yesterday i was voting answer b, but now comparing these two pictures i think it's much better the 'a' answer.
i think the flatness it's more important reading a single spl graph. am i correct?
please take a look to these pictures

red graph represent my room with some kind of treatments and the other one is concerning empty room


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## irombeach (Sep 7, 2010)

let us look to this comparative picture of my waterfalls from 30 to 80hz.

please note that the red graph is the room WITH some panels.
i don't want to examine where panels are or which kind of panels.

i'd like to READ and understand WHAT PLOT can tell me.

i've found three 'curves' A (approx 30 hz), B (approx 45) and C (approx 50, 52 hz)

my eyes see :

1) A curve has remained the same (no faster decay)
2) B curve is quite the same
3) C curve is DISAPPEARED

so i think we obtained a little improvement around 50hz, am i correct ?


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## irombeach (Sep 7, 2010)

here enclosed a picture from 80 to over 130/140 hz.
till 90, it's seems we're getting worse.
after 90 hertz things are going better.


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## irombeach (Sep 7, 2010)

and finally the last picture till 250 hz.
its seems to be a 'chaos' 
generally pressure level is lower in the red graph (room with panels) but we have not any kind of linearity.
ok i've finished.

can someone tell me something ?
thanks
ale


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## Wayne A. Pflughaupt (Apr 13, 2006)

> So, reading a plot, what are we looking for?
> 
> a) fast decay (vertical downhill from t1...t2...tx)
> b) general flatness of the graph?
> c) bot of them?


Both but primarily “A.”



















Courtesy of Real Traps​



> let us look to this comparative picture of my waterfalls from 30 to 80hz.


No reason to, bass treatments rarely have an effect down that low.




> here enclosed a picture from 80 to over 130/140 hz.
> till 90, it's seems we're getting worse.


Whatever that anomaly at 90 Hz was, it wasn’t caused by any room treatments.




> and finally the last picture till 250 hz.
> its seems to be a 'chaos'
> generally pressure level is lower in the red graph (room with panels) but we have not any kind of linearity.
> ok i've finished.
> ...


Someone at our Acoustics Forum probably can – which is where I’m moving this thread.  But from what I see with the Real Traps graphs, treatments do tend to reduce peaks.

Regards,
Wayne


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## grn1969c10 (Sep 18, 2008)

I haven't had REW set up for a few months, so my memory may be a little wonky. Right off the top I would suggest using a longer "time" to get a better feel for the decay rate. The posted graphs show 300ms which is the default (I think). Try 500ms or something longer. I don't think you need to redo the measurements - just reopen them and modify the time range. Note the sample waterfalls that Wayne posted.


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## DanTheMan (Oct 12, 2009)

I'd agree with Matt, but like go for 1000msec. Bass can take forever to decay. I'd also generate some spectrograms of the same time frame. I believe they are a bit more pertinent psychoacoustically and will help you get a better grasp of the situation in conjunction with the CSD. Toss an RT60(simple to read though paints with a broad brush) in there and all will be clearly understood. I actually like log sweeps from 20-20kHz for the most part. If it's so subtle you don't see it there, it's subtle. 

Dan


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## jlird808 (Nov 2, 2010)

Sorry to reopen a year+ old thread but did u resolve this irombeach? did u add more bass trapping and retest? I'm trying to tune my low end too.



grn1969c10 said:


> Right off the top I would suggest using a longer "time" to get a better feel for the decay rate. The posted graphs show 300ms which is the default (I think). Try 500ms or something longer. I don't think you need to redo the measurements - just reopen them and modify the time range.


Where do u adjust the ms time setting? Its not in the same place as the db and hz adjustments 

Thanks!


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## Wayne A. Pflughaupt (Apr 13, 2006)

In the Waterfall window, look for the box labeled “Time range (ms).” 

Regards,
Wayne


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