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Discussion Starter · #1 ·
Hello...
here i am with my first waterfall.
i hope image is ok.

what can you tell me about this first graph of my room?
it's taken without any kind of absorber.


thanks a lot
Alessandro
 

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Wow, did you really take your measurement at 120+ dB? Please re-run the Calibrate SPL routine and take another measurement.

Waterfalls are mainly useful determining low frequency decay times, so the only room treatments they will help you analyze are bass traps. The “absorbers” you mentioned work on the upper frequencies. The correct graphs for upper-frequency decay times are RT60 or Energy Time.


Regards,
Wayne
 

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Discussion Starter · #3 ·
hy wayne and thanks for your prompt reply.
first problem is my english.
when i say "absorbers" i mean bass traps. (if bass traps are : tube traps ).
which is the correct name for rectangular wall panels made of (or filled with) rock wool?

second problem : i did SPL calibration.......and so for me these are correct values BUT....
obviously, i'll re calibrate spl and i'll re-send a new graph.


but....if this measurement is correct, can you tell me what can you see inside it?
thanks
alessandro
 

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No problem with the English, allesandro, your English is much better than my Italian. The only thing I can say in Italian is “fettuccini.” Hee hee...

but....if this measurement is correct, can you tell me what can you see inside it?
There’s not much to tell really. The only thing the waterfall will tell you is if the bass traps have been effective. That will require two measurements in the room: one before the bass traps are in the room, and a second one after they are in place. This “before and after” method could also help you determine the best place to locate the traps, but I think the corners of the room are usually what is recommended.

Regards,
Wayne
 

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Discussion Starter · #5 ·
...ok Wayne....this evening i'll take a new measurement.

the correct word is "FETTUCCINE"....

see you tomorrow....

thanks
ale
 

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It appears to me that your front speakers are set to a much higher level than your sub. So you may have calibrated REW's SPL level using the sub test tone to ~75dB, but when you measure the sub with the mains, they are much higher and taking up much of the display. Does it sound as if the mains are much louder? The effect of the bass traps might be easier to see if you take your measurements with the sub alone, without the mains connected.

The perspective is a little different than what I am used to seeing in waterfalls. It is as if you are higher up, looking down more on the contour. Did you adjust the y dimension? I think the default is 100.

Bill
 

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Discussion Starter · #8 ·
ok...i'm here with new measurements.
first of all, thanks in advance to Wayne and Bill.

:devil:
i've three pictures : left channel without tube, left channel with tube (one and only)
and a comparison file with overlays.


calibration was done for fullrange speakers.
i've no subwoofer cause i have a stereo system.

please let me know......
 

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Discussion Starter · #11 ·
hi Wayne, i don't understand.
Isn't yellow graph lower than the violet one?
at the same time, i see that yellow graph is under the violet.
Do you mean that differences are too little?
what i see in the picture is that, for example, at 35 hz, the yellow one is decreased of 5db.
am i wrong?

regarding...what i hear, with two tubes on the corners behind the speakers, i think that scene is much wider.

thanks ale
 

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Discussion Starter · #12 ·
Hi Wayne,
i don't understand....


isn't the yellow graph 'lower' than the violet one?
i say that at 35 hz (for example) the yellow line is 5d lower than the violet.

do you mean that differences are too little to be heard?


i think that....
i can hear a wider scene with two tubes on the corners behind the speakers.


i know that we need an higher number of bass traps but first of all i'd like to see
'real improvements' and not ideas of improvement.

ale
 

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It’s a common mis-reading of a waterfall graph. The yellow graph looks better because it is “lower. However, it’s not “lower” because the bass traps made a difference. It’s “lower” because the second reading was taken at a lower SPL level. It would be easier to tell an improvement in decay times if the two readings were level-matched. This post should explain things better.

Regards,
Wayne
 

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What you can do, Ale, is to look at a peak well above where the trap should have an effect, say the peak at 220Hz in the non-trap graph. See what the level is, then compare to the level of the same peak in the with-trap graph. In the SPL & Phase Controls, enter the difference in the Offset field. Add Offset to Data to apply the change to the underlying data, and regenerate the waterfall. With a little tweaking, you should be able to align them at the high end, and then see if there is any effect at the low end.

If the change in the decay is very slight, you may have to extend the time range to see where the peaks are decaying into the noise floor.

Bill
 

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Discussion Starter · #15 ·
ok, thanks a lot Bill and Wayne.

for Wayne : when you say : "It’s “lower” because the second reading was taken at a lower SPL level."
do you mean i take the measurement at a lower "volume" ?
if yes , i will re- take the measurement and i should see that two graphs will be quite identical?????
 

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for Wayne : when you say : "It’s “lower” because the second reading was taken at a lower SPL level."
do you mean i take the measurement at a lower "volume" ?
No, I mean if you want to compare before and after graphs, it’s helpful if they are both taken at the same SPL level. If not, the one taken at a lower SPL level “looks” better than it really is. If not, you can always offset the data to make the two readings match, as Bill suggested.

Regards,
Wayne
 
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