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Old 23rd August 2010, 01:18 AM   #41
gedlee is online now gedlee  United States
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Green Glue is just Melamine glue, identical to the stuff from Franklin. Liquid Nails for Subfloors claims to "never harden". When left out for years, I know that it does, but thats in open air and I'm told in a sealed situation like between dry-wall will not harden. Standard Liquid Nails is intended to harden - you have to get the Sub-Floor stuff.
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Old 23rd August 2010, 01:42 AM   #42
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Melamine huh, I thought I read Urethane. I relooked it up, Latex Polymer is the only ingredient listed, other than water. Wonder what I was looking at. Maybe I made up the urethane bit, or maybe its changed. Melamine glue is listed as Polyvinyl acetate, is that the same thing, or were you just saying they were similar products? Curious, because if what you say is true, that sounds like useful information. I'm sure a 5 gallon container of Franklin Melamine glue is cheaper than 5 gallons of green glue.

I don't recall where you said you get your urethane from, but I know any source I've found is expensive. Is it just the urethane for mold pouring and such? Is it a urethane foam (doesn't feel it)?
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Old 23rd August 2010, 02:25 AM   #43
gedlee is online now gedlee  United States
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The polyurethane is extremely expensive - yes. Its over $100 a gallon. I use Innovative Polymers (Innovative Polymers, Inc.)

The Melamine glue just looks and acts like the Green glue, but I was not sure of what the ingredients were, just that Green Glue was far too expensive and Melamine glue was quite reasonable and works well. Thats what I would use if I do any wall structures again.

I use polyurethane foam to seal cracks and holes, but not as the CLD layer.
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Old 23rd August 2010, 03:46 AM   #44
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How much will a good CLD wall treatment attenuate bass ringing? For example, would it improve my situation? Here is my LF room response as a waterfall plot... The signal decays by about half (in terms of db) in something like 200-300 ms, but some of the modes keep ringing ring for another 300 ms or so.

Click the image to open in full size.
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Old 23rd August 2010, 06:57 AM   #45
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While I hate to speak for Dr. Geddes ... pjpoes, it was not specificaly aimed to Dr. Geddes. Thanks for the comments.

Quote:
Originally Posted by gedlee View Post
... Sounds like they made the CLD wall too stiff. It really has to be quite flimsy to work right - think or a hanging sheet of cloth - very limp. Most often that I have seen people try this technique they make it far too stiff and it kills the effect.
Yes. The stiffness seems too strong. That is why I have questioned if damping 0.4 is even better than nothing.
I asked workers to do CLD wall with half of studs (every 4' not 2'). I told them that I don't mind the cracks in joints between boards. Didn't help.
For design I have used empiric formula (found in A.Everest book) Fo= (1/2*pi)*SQRT(ro*c*c/m/d) and for center frequency about 50Hz and double 1/2'' gypsum board gives me 3'' gap. Gap was filled with 40mm glass insulation. Maybe it was not a good idea according to Toole's book. Because it softens resonance of the wall therefore the efficiency. Unfortunately I read it later.


Quote:
Originally Posted by gedlee View Post
I use 1/2" drywall and historically used Liquid nails. My polyurethene mixture would work better, but I have not used that on a wall structure. the Liquid Nails (for Subfloors) is spread about 1/4" with a flooring trowl. I attach the first layer to RC1 resilient channel, which is attached to the studs, then the second layer is just glued on the first. You have to hold the layers together with screws until set, then just remove the screws.
Resilient channel was not in stock here - very special here. Workers used 1/5" foam pads for supports.
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Old 23rd August 2010, 07:17 AM   #46
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Quote:
Originally Posted by DougSmith View Post
How much will a good CLD wall treatment attenuate bass ringing? For example, would it improve my situation? Here is my LF room response as a waterfall plot... The signal decays by about half (in terms of db) in something like 200-300 ms, but some of the modes keep ringing ring for another 300 ms or so.

Click the image to open in full size.
That is why it is made - attenuate the bass ringing. Consequently it softens resonances, making them broader and more overlapped. There is a difference if you try to flatten out narrow 10dB peaks and 15 dB gaps spaced well appart or 5dB "wiggles" which rings 1/3 of time.
Btw. Your measurement is not spatialy averaged - there are separate reflections showing up which will be averaged out if done properly and only resonances (modes) will stay. Point of interest of CLD wall treatment is only up to 200Hz.
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Last edited by MethMan; 23rd August 2010 at 07:20 AM.
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Old 23rd August 2010, 07:59 AM   #47
gedlee is online now gedlee  United States
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Quote:
Originally Posted by MethMan View Post
Resilient channel was not in stock here - very special here. Workers used 1/5" foam pads for supports.
Well that would completely defeat the whole technique. Resilient channel is not an option, it is a requirement. Its what makes the whole thing work. In Thailand they did not have resilient channel either, but we fabicated some from metal studs which seem to be available all over the world. I can see no way that the standard contractor would ever do this kind of wall right. they just don't "get it" and end up messing it all up. I have never seen a contractor do it even marginally acceptable.
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Old 24th August 2010, 01:40 AM   #48
pjpoes is offline pjpoes  United States
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Ok let me rant for a quick moment. Also let me add, this is directed at nobody on this forum. When Doug posted his waterfall plot, it reminded me of a pet peeve of mine. I see on so many forums talking about room dampening and modal ringing that suggest that special DSP eq's can some how reduce it. I don't see how. Also, they show waterfall plots that they suggest prove reduce modal ringing. Ok so this is my rant. My understanding of the concept of dampening is that its not an overall amplitude reduction, its that the amplitude is steadily reduced over time.

Ok so here is the problem I find with the posted graphs that they suggest is offering dampening, they show overall amplitude reduction, which of course will show up over time too, and then taught "See it dampened the modes". I'm sorry, but thats just eq, and thats all an EQ can do. Many of the LF absorbers out there do offer dampening, just not nearly as much as claimed, and in my opinion, not enough to be useful.

Dr. Geddes a room acoustics white paper that addresses this aspect of eq vs dampening would be a good one (assuming at least some of my argument is correct).
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Old 24th August 2010, 02:05 AM   #49
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In Floyd Toole's book on loudspeakers and rooms he talks about the functonal equivalence of notch filters at modal peaks and bass absorption in a room. Is there any real difference in the time signature of the decay that can be achieved by these two different approaches?

I think it might be possible to achieve a faster decay at bass frequencies by having one sub out of phase with another. The WF plot I generated with my subs operating that way looked cleaner than the one I showed here where both subs are in phase with the mains. It wasn't a controlled experiment, however.
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Old 24th August 2010, 02:45 AM   #50
gedlee is online now gedlee  United States
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Matt

When one is looking at a waterfall, then this is a transient picture most times derived from some steady state measurement. The logic behind what you say is "sound" (Pun intended) in that is that no damping can affect the sound in the room before this sound reaches the damping. This much is obvious. This means that the direct field cannot be affected by room damping and hence any lowering of the sound of the direct field due to room damping must be incorrect. But at low enough frequencies it becomes impossible to detect or seperate the direct field from the reverberant field and only the steady state can be measured with any certainty. Hence it is reasonable in the modal region to see a lowering of the initial response due to the sbsorption. But if someone shows a lowering of the intial CSD above the Schroeder frequency then something is wrong, and its usually a failure of the assumption of determinism - that the sound field is stable and stationary at those frequencies. Its not. Take the same measurement several times on different days - temp and humidity - and you will get different results in the details and especially at supposed "modal peaks" (which do not exist in the statistical region). Take enough measurements at these frequencies and eventually you will get the data you want - just throw away all the other examples!

But Doug is also correct in what he says for "modal" frequencies, but alas its not true at statistcal frequencies. Thats the whole problem - the direct field and the reverberant field are different in the HF region and correct one does not necessarily or actually cannot, correct the other.
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