Cloud Effects

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Postby bert stoltenborg » Fri Apr 28, 2006 12:30 am

Bob wrote:David French

I did a little study on the effects of 4" 703 clouds on the modal resonances of my 159" x 118" x 96" room; hopefully it's useful to someone.

I looked at your animation gif -- it looks to me that the modes were not affected at all, but rather it simply made the room quieter and kept the modes. Is that your read too?


Not to be a nagger, but some autohrataazzz like Thomas Salava or Earl Geddes tell you you often have to EQ the modes.
It seems to be difficult to affect modes with absorbtion, I guess.


 :D
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Postby David French » Fri Apr 28, 2006 12:59 am

?!? What?  Difficult to affect modes with absorption?  I have some data to show you later then.   :twisted:

Bob, I was not thinking that at all.  for under 100 Hz, yes, but the modes above that show significant broadening and faster decay rates, which are definitely signs of imnprovement.  No, this is not the most efficent use of the material, but I was just wondering what the clouds by themselves do.  Kinda reminds me of  hangers, which I still dont; understand (if anybody else does, please clue me in).
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Postby Bob » Fri Apr 28, 2006 3:15 am

hangers, which I still dont; understand (if anybody else does, please clue me in).

I have a theory about them.
It has to do with wave guides, and edge decaying pressure fronts, and panel inertia and flex, and ..
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Postby David French » Fri Apr 28, 2006 4:16 am

Bob, are you joking?
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Postby Bob » Fri Apr 28, 2006 4:23 am

David French:

I don't think so. Why, did I say something stupid enough to be funny ? :)
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Postby David French » Fri Apr 28, 2006 4:27 am

This set off my joke alarms:

It has to do with wave guides, and edge decaying pressure fronts, and panel inertia and flex, and ..


Have you ever seen a study involving hangers?  If you have a theory, would you like to post it in a thread and maybe we could make a discussion of it?
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Postby David French » Fri Apr 28, 2006 4:54 am

Bert wrote:It seems to be difficult to affect modes with absorbtion, I guess.


David wrote:I have some data to show you later then.


And here it is:

These are from my 404 x 300 x 244 cm room treated with about 1.7 cubic meters of 703, half in 4" thick panels and the other half in 2" thick panels.

Note how absorption shifts the center frequencies of the resonances.  BTW, if anyone has resources where I could further study this phenomenon, please let me know.
Attachments
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after.gif (25.12 KiB) Viewed 5970 times
before.gif
before.gif (32.48 KiB) Viewed 5970 times
Last edited by David French on Fri Apr 28, 2006 8:39 pm, edited 1 time in total.
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Postby bert stoltenborg » Fri Apr 28, 2006 10:08 am

Hmmm,

5 dB more output around 45 Hz...

A PA guy would kill for such a free lunch

:D
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Postby avare » Fri Apr 28, 2006 2:25 pm

I feel so inadequate.  Ni humour, no subtle analysis.  Just a "Great Stuff!"  Thanks

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Postby David French » Fri Apr 28, 2006 4:10 pm

This is nothing.  Man, I'd love to look at Paul's or Mark's before and after data with this software (if they have it).

So it looks like the traditional '703 across the corners technique' starts to break down at about 50-60 Hz.  Yet, the ringing of the 45 Hz behemoth has been reduced by about half.  It seems that in my room a good solution would be porous with one pressure device tuned at about 50 hz or so.
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Postby avare » Fri Apr 28, 2006 5:12 pm

So it looks like the traditional '703 across the corners technique' starts to break down at about 50-60 Hz.  Yet, the ringing of the 45 Hz behemoth has been reduced by about half.  It seems that in my room a good solution would be porous with one pressure device tuned at about 50 hz or so.


Am I missing something?  I know I am good at that.  The clouds are in the height plane, 8', where the lowest mode is ~70Hz.  Lower modes are from untreated planes in this example.

Clear as mud:
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Postby David French » Fri Apr 28, 2006 5:37 pm

I think you missed this:

I wrote:These are from my 404 x 300 x 244 cm room treated with about 1.7 cubic meters of 703, half in 4" thick panels and the other half in 2" thick panels.


from this post.

I'm guessing you thought that the latest graphs were from teh clouds alone?  What I don't get is how you thought this graph looked anything like this graph.  Maybe I'm the confused one?
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Postby avare » Fri Apr 28, 2006 6:07 pm

I'm guessing you thought that the latest graphs were from teh clouds alone?  What I don't get is how you thought this graph looked anything like this graph.
Maybe I'm the confused one?


Thanks.  

Maybe I'm the confused one?


No, I am.  Don't even try to be as confused as I am.  It isn't worth it.

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Postby David French » Fri Apr 28, 2006 6:22 pm

So everything's all clear now?
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Postby Zaphod » Fri Apr 28, 2006 7:02 pm

Woah!

That's for the guys in the HT forums saying that
with absorption you can't handle low frequencies  :mrgreen:

Bert,
what does PA mean?

Bob,
Just some random and possibly meaningless thoughts

I think that you should consider that, if i understand well, the first
measurement was done with the mic in one corner and a sub (or
a speaker?) in the other, so that what we see is mostly modes.

See also that there are red isles that "emerge" from the blue modal
peaks, expecially in the twin clouds pic.

Also, the energy losing of the modes is good per se.
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Postby David French » Fri Apr 28, 2006 7:23 pm

Zaphod, PA means Public Address, in other words, sound reinforcement for concerts, etc.

To make things clear, the cloud tests were with the speaker in the corner, while the general room treatment tests were with the speakers in a much more traditional placement.  The second test was not meand to be scientific; rather it was just meant to be a basic illustration of what a fair ammount of fiberglass panels can do.  Note that this is nowhere near the % volume that paul and Mark used.  Mine only uses about 5% of the room's volume as porous absorption.
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Postby bert stoltenborg » Fri Apr 28, 2006 7:28 pm

HOW COME THIS 40 HZ IS IN THE TREATED ROOM 5 Db LOUDER?


:bang
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Postby J.F.Oros » Fri Apr 28, 2006 7:48 pm

bert stoltenborg wrote:HOW COME THIS 40 HZ IS IN THE TREATED ROOM 5 Db LOUDER?

Not only that 40 Hz mode but a lot of the initial energy (the red curves) appears to be higher in the after-treatment diagram, so maybe it's just a display thing (like a normalization or something) ?  :|

David, I prefer to display only the coloured lines (not full slices), that way you can see the initial curves if they are masqued by the latters  :)
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Postby Zaphod » Fri Apr 28, 2006 7:51 pm

Flaviu,

i think that most of the rising energy are just nulls being
wiped out of the room.

The 40 hz peak instead, well it gets well above the average
response.  :bang
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Postby David French » Fri Apr 28, 2006 8:41 pm

I have updated the before and after graphs to reflect the true levels.  I have no idea why the levels weren't accurate, but they sure weren't.  The new graphs are with volumes, gains, and software offsets untouched.

Flav, you're probably right about the filled vs. line graphs, but I just can't resist the prettiness!
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