# Waterfall graph - are my acoustics OK?



## halfgaar (Dec 12, 2012)

Hi,

I'm somewhat new to these forums, so I hope I'm not asking the FAQ's, but I was wondering if we have a reference database / forum section where people posted their responses, plus explanation/pictures.

I would like to compare my room decay response to that of others. 

I know how to judge a room by ear and can compare rooms and can somewhat guess the effects on imaging and model resonance when I stand in a room, but I'm new to making measurements (so I have none to compare), so I have no frame of reference.

This is the waterfall graph of my room with two Acoustic Energy's 120 and DIY sub:










The room sounds pretty good when it comes to acoustics. It's about 20 m² (215 ft²) big. There are long heavy curtains, a soft couch with blankets, etc. Imaging and definition are very good in this room.

I was just wondering, how does it compare to other rooms? To people who do have a frame of reference: are the decay characteristics of this room OK?


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## morca (Aug 26, 2011)

It look,s great!!
Is it your HT room or the living room?


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## JohnM (Apr 11, 2006)

Try adjusting the scale per the graph posting tips for easier comparison with other plots, at the moment you have a very large SPL range in the graph which compresses things quite a bit. As far as frequency range goes, waterfalls are most relevant up to 200 or 300 Hz or so.


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## halfgaar (Dec 12, 2012)

It's my HT room, which luckily is more easily damped. 

Here is another graph:










I did read those graph posting tips, but the scales mentioned don't really work well for the waterfall. If I set min to 45, you just see a bunch of peaks.

I'm quite surprised that waterfall graphs are only useful till 300 Hz BTW. That's where my midrange starts, and when I try to make echo's in a room, it's definitely midrange frequency.


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

IMO the best lower limit for a waterfall graph is roughly the room’s ambient noise level, which will be ~35-40 dB in most rooms. Also, a graph with a 300 ms window would be helpful for comparison. That said, it appears you have fairly consistent decay times across the frequency spectrum, except for at ~20 Hz.

Regards, 
Wayne


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## halfgaar (Dec 12, 2012)

Here's the graph again with a min of 35dB:










About the 20 Hz and 40 Hz peaks; I guess I have to build bass traps for those. More for the 40 Hz, because that frequency is much more present in music.


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## morca (Aug 26, 2011)

like i sad ,exellent !!!
40 hz could be the roomgain,i also had that problem.


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## halfgaar (Dec 12, 2012)

Great then


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## Phillips (Aug 12, 2011)

Looks good.

Instead of 3000hz try scaling to 300hz. Scale 10 hz > 300hz.

Waterfall graphs have no use above 300hz.


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## morca (Aug 26, 2011)

above 300hz problem,s can be solved to.........


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## halfgaar (Dec 12, 2012)

Why do waterfall graphs have no use above 300 Hz? As I said before, in rooms with echo, I can clearly hear very mid-range sounds reverberating around the room.


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## JohnM (Apr 11, 2006)

Just the wrong tool for the job, look at the ETC (here is an article on reflections and the ETC.


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## halfgaar (Dec 12, 2012)

One thing the article states, is: 



> Another type of acoustic measurement that could be used is one that combines time, energy and frequency in one chart. These – in their waterfall or spectrogram forms – are often used to analyze low frequency modal decay in small rooms. The benefit to using this type of measurement is that it contains spectral information – which is notably missing from an ETC. The problem with using this type of measurement in reflection analysis (i.e. above 250Hz) is that there are no acoustic measurement packages out there that I know of that provide these data views in a manner where trends and information can be visually interpreted. For such a measurement to be effective it must be presented with frequency axis smoothing (e.g. 1/3rd octave) otherwise the data is almost impossible to interpret.


Would it be possible for REW to smooth the frequency axis of a waterfall plot? I think it would make it a lot easier to read.


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## JohnM (Apr 11, 2006)

halfgaar said:


> Would it be possible for REW to smooth the frequency axis of a waterfall plot? I think it would make it a lot easier to read.


There is a smoothing setting in the waterfall controls.


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