Another Green Glue Question

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Re: Another Green Glue Question

Postby Eric.Desart » Sun Aug 15, 2010 10:50 am

Just short,

I don't feel quiet well. I see I've some PB's still to answer. Sorry guys, bit patience.
All out of my head without checking any data now.

Flanking in labs: Once the lab isolates (frequency related in 1/3 octave bands) about 8 dB better than the sample wall the impact on the measurement will be very small (<1 dB on these bands). More difference is better, but you're speaking in fractions of a dB.

As far as I know this limitation will occur mainly in the highs, which is rather recognizable.
Since the highs are not that defining in most TL single number ratings, the phenomenon is mainly interesting to check these highs but will rarely be of significance in practical use in forums like this.

In the lows, normally one can expect lab flanking being of little influence certainly with drywall systems with their typical double leaf behavior. Walls are designed also to test single leaf solid walls which normally give higher TL in the lows.

Limitations in labs can often be caused by much more difficult to pinpoint effects, like niche effects, how exactly are these walls build in, the shape and volume of the rooms, the way the sound field is exited and the accuracy of the absorption measurement at the receiving site. All these phenomena are limited in effect, but really can cause some differences.

As far as GG goes in function of stiffness. Not only the bending radius plays a rol (displacement), but also the acceleration. As an example. One loves to compare GG walls with walls directly mounted on the wooden stuts. This causes this structural resonance limiting a whole lot in the total curve. This direct mounting limits the amplitude (displacement) yet it's exactly there that GG shows its qualities. GG is very effective in the coincidence area where the displacement are small and the wavelengths relative short.
Hence, without knowing the exact answer without seeing tests, I believe that Ted's approach here is too limited and over-simplified.

In this topic some weight is given to uncertainties in function of lab flanking. In practice I believe with the situations described here none are limited or influenced by lab flanking.
What I do think which can influence measurements, and is often unclear described, is, if you build a double leaf system, do you build walls in the separated brick/concrete walls of the decoupled measurement rooms, or do you mount the panel sides both within the thickness of the same single brick/concrete wall. Such walls can easily have thicknesses of 1 foot (or somewhat less). Hence you can mount a double stud wall on that solid brick/concrete wall or over the cavity separating this lab double leaf system of solid walls.

I don't know exactly how every lab is build of course. I have measured in different labs already, both accredited, where the principle build-up caused a noticeable difference in the lows.

And of course the weakest paths define the end-result, wherever they originate from (flanking and others). In practice one will rarely find a field TL equaling a lab TL.
Also Brian checked differences in his standard lab he chooses for the GG measurements depending on the measurement direction. Theoretically Isolation is reversible (not taking flanking effect into account), hence these differences DO NOT RELATE simply to flanking caused by the TL of the lab itself.
Brian (or the lab itself) choose the measurement direction for which he has the feeling that they most resemble the Canadian IRC/NRC results (in function of compatibility). In as far this is correct (without any judgment whatsoever) we only have Brian's word for it.

The discussion about Lab flanking effect feels more theoretical than of any practical significance to me in this topic.

Without being directly comparable: My first experience with GG was meant to suppress or diminish an annoying ca 40 to 45 Hz resonance of a ceiling with some extremely old, but very hard and difficult identifiable boards (some old type of material, at least many decays old - nobody knew - in a >100 year old huge house).
With an additional 9 mm (or was it 12, no I think 9) gypsum board glued with GG I couldn't excite this resonance anymore, however .....
The fun part was the settling time of GG, where the first days I found it just lost money, energy and work, after a good week it was better but not really convincing, and after a month (didn't do exact tests to know how it reacted on a day by day basis) I was amazed by the result. No way I could still excite this explicit resonance.

AND THIS CAN BE IMPORTANT IF OTHER LABS DO TESTS. BASICALLY YOU CAN'T JUDGE OR MEASURE A GG WALL SHORTLY AFTER MOUNTING. That's why Brian has to prepare this stuff long beforehand (settling time which is very important for GG and which is a very time-consuming process. This is not a matter of days).
I once laught with him about this, asking him if he was waiting for a month after mounting, on a chair, laying backwards and staring at his wall before executing the measurement. That way these measurements should become extremely costly by blocking such a lab for LONG periods.
Hence judging GG measurements of other labs calls for checking which procedure they used which for GG isn't a standard approach at all. It's not even simple to imagine what the best method should be.

It's not because you see a lab measurement that it is a representative measurement, certainly when side-effects can play a rol. A lab will measure what a customer asks as per standard, and will describe the build-up of such a wall in as much detail they have, but are dependent here of the supplier or customer (at least for the part they can't check themselves).
Therefore it's important to check COMPLETE reports, which still not means that they contain all influencing parameters.
Therefore, not seldom a lab will store samples (not always, only when this can have sense for future reference) of things they measured.
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Re: Another Green Glue Question

Postby seb » Sun Aug 15, 2010 11:55 am

Rod Gervais wrote:
However, I will be mindful of your suggestion.


Thanks, coming from you that means a lot.......



Rod, I have lurked in these forums a bit and I have bought and read your book but I don't really know you that well to be able to tell if you are taking the piss... (is that an Aussie expression or is that understood across the Pacific Ocean?)

Anyway, subject to the Client's confidentiality I expect to post any useful results back here.

Eric, I am aware of the 30 days or so of curing time. The local Australian distributor claims that after 10-14 days the results are "at about 80%" but I am not sure if this is a gut feel or based on measurement.

I have thought some more about the issue of damping at low frequency and whether or not a different kind of test would be useful to help show Green Glue working. As you know, the test with RFC was not particularly successful from this point of view. If I have some time then I would probably like to try a swept sine test of TL. It may be a lengthy test as I am thinking to use 4 source-room speaker positions and several microphone positions in the receive room. The purpose is to show up any benefits of GG that a broadband pink noise test doesn't. What prompted this is the RFC test but of course if the broadband test on the double-stud wall shows the GreenGlue working as expected then I will probably skip the sines.
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Re: Another Green Glue Question

Postby Eric.Desart » Sun Aug 15, 2010 12:08 pm

Just a comment.

If you mount walls with RC (resilient coupling) you introduce an additional factor which can dominate the results.
Hence the conclusion: I speak about decoupled wall since the panels are one- or two sided mounted on RC is an oversimplified conclusion.
Such an RC has its own resonance frequency.
If you have large cavities and a low MSM from a double leaf system itself RC can even become the LIMITING factor making the wall worse in the lows.

I don't give rules of thumbs here, only pointing out that RC is NO NEUTRAL DECOUPLING, which influences or can influence the comparison between these measurements. Hence as long as you can't isolate this phenomenon you can't express conclusions about the isolated effect of GG.

You want measurements which are complex and complicated, therefor costly.
I do agree that it are interesting questions, and I also should like a series of measurements about GG to answer questions of mine. I'm as well critical about some cost/gain questions. About GG in itself I agree it's a very good product which I like to use.
I should need to restudy all the available measurements to check if my old questions still remain (which I superficially expect to do).
While Brian (the designer of the stuff) is a VERY objective and analytic engineer there are still commercial motives involved in what you see and don't see. I'm rather convinced he knows more than he (the company) tells related to cost/effect issues.

Fantasizing about some theory is maybe fun but still stays gambling, no matter how much pages we fill with them.
A hypothesis is something to be checked on its validity, nothing more. And therefor you need the means or budgets to check it.
I gave my low frequency GG experience for something as well.

++++++++++++++++++++++++++++++++++++++++++++++++++++++

If i just listen to my belly, without any check or clear explanation, hence with a low scientific value, I should say that GG works best were the problems are the most dominant and explicit, and that for a better wall with larger OC, in as far there is a difference, the additional GG gain will be lower than for a worse smaller OC studs distance.
But don't take this as science ...... unless tests could deny or confirm that.

Maybe a stupid analogy which flashes trough my mind now. See GG as an equalizer trying to restore TL to its logical Mass-law behavior. The more you approach this logical behavior the less there is for GG to improve.
In how far this is just a poetic license or has some deeper backing is not clear yet. For now it's a flash.
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Re: Another Green Glue Question

Postby Rod Gervais » Sun Aug 15, 2010 3:21 pm

seb wrote:
Rod Gervais wrote:
However, I will be mindful of your suggestion.

Thanks, coming from you that means a lot.......

Rod, I have lurked in these forums a bit and I have bought and read your book but I don't really know you that well to be able to tell if you are taking the piss... (is that an Aussie expression or is that understood across the Pacific Ocean?)

Seb,

I think it translates - although it is not a typical American term - but if it means what I believe it means (which would be: "Am I being sarcastic?") then the answer is no - I am very sincere - I have a lot of respect for you - as I do for most of the people here.
Rod

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Re: Another Green Glue Question

Postby seb » Sun Aug 15, 2010 10:04 pm

seb
 
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Re: Another Green Glue Question

Postby Eric.Desart » Sun Aug 15, 2010 11:01 pm

Seb,

If you still have comments or remarks about the topic ITSELF?
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Re: Another Green Glue Question

Postby Rod Gervais » Mon Aug 16, 2010 1:58 am



Seb,

nope - as I said - I respect you - nothing behind the remarks I made other thasn what they are at face value.

I do not treat people that way.......... if I have something to say to anyone I come out and say it - one thing I am not is bashful.....

You can count on my meaning each and every thing I say....... and if I find myself to be wrong - I am not worried about admitting it in public.....
Rod

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Re: Another Green Glue Question

Postby seb » Mon Aug 16, 2010 8:53 pm

No worries. I will post here when test data becomes available. I will also hit up the Australian distributor. Some lab testing has been done - including comparative testing - but it is not publicly available.

Regards,

Sebastian
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Re: Another Green Glue Question

Postby Eric.Desart » Tue Aug 17, 2010 6:08 pm

seb wrote: I will post here when test data becomes available.

That indeed should be very strong and useful.

The risk is always that you see these measurements confirming quality, but not these which put question marks in certain applications.
Both are important to understand a material.
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Re: Another Green Glue Question

Postby Ido » Wed Aug 25, 2010 11:18 am

What I would ask from Green Glue is test data of 3 layers of drywall with 2 intermediate GG layers.
This is for those scenarios where the standard 2 layered drywall GG is not enough, and higher TL is needed.
cheers all,
Ido
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Re: Another Green Glue Question

Postby Eric.Desart » Sat Aug 28, 2010 8:26 am

Ido,

I haven't checked now if official measurements exist (can't remember). But Brian had done some kind of tests with it.
If I remember correctly (hence conditional) he said that the same amount of GG divided over the 2 inner surfaces give better isolation than 100% in 1 layer between 2 boards.

But I'm not sure anymore in function of his exact wording about this. It should be searched what Brian exactly told about it. Maybe Ted can check with Brian.
Or Bob, our acoustic net database, can find or knows something more about this.
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Re: Another Green Glue Question

Postby Ted White » Sat Aug 28, 2010 10:55 am

Eric your mind is as sharp as ever. Splitting a fixed quantity of damping compound into two layers between three layers of mass results in more efficient damping even if the total mass of the two scenarios is the same.
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Re: Another Green Glue Question

Postby Ido » Sat Aug 28, 2010 5:17 pm

Eric, Ted, thanks.
My question though is not about getting relatively more damping per given GG,
But about getting overall higher TL using drywall & GG, in whatever way, more than the "standard" 2 layered drywall with intermediate GG, and with no limit on the GG quantity.
Obviously, the next logical step is 3 drywall layers with 2 intermediate layers of GG (in whatever quantity deemed necessary).
the question is, what would be the magnitude of the TL dB gain.. more like 3 dB? More like 6 dB?
This is a real life scenario question, where sometimes the standard GG wall is not enough, especially for LF.
For a small area of wall, I would just go ahead and do the 3+2 drywall/GG,
But for big areas of walls/big projects, it's a real issue that needs the info.
Cheers,
Ido
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Re: Another Green Glue Question

Postby Ted White » Mon Aug 30, 2010 2:38 pm

I would say that if the framing is competently decoupled, as with a double stud wall, damping would take a back seat to mass and cavity depth. Certainly damping will not affect the placement of the LF resonance point. Mass, cavity depth, and the presence of proper absorption (low/medium density insulation) will determine the MSM resonance frequency.

The presence of a damping compound would still reduce the effects of panel resonance at the MSM point through coincidence. So I might suggest looking at Eric's excellent MAM frequency calculator (linked on this site somewhere) and base your calculations based on the primary drivers of mass, cavity depth absorption. This defines the LF resonance, which determines low frequency attenuation. Then damp.
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Re: Another Green Glue Question

Postby Ido » Tue Aug 31, 2010 9:16 am

-edit-
Last edited by Ido on Tue Aug 31, 2010 9:19 am, edited 1 time in total.
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Re: Another Green Glue Question

Postby Ido » Tue Aug 31, 2010 9:17 am

hi Ted,

Ted White wrote:I would say that if the framing is competently decoupled, as with a double stud wall, damping would take a back seat to mass and cavity depth. Certainly damping will not affect the placement of the LF resonance point. Mass, cavity depth, and the presence of proper absorption (low/medium density insulation) will determine the MSM resonance frequency. ..


I'm not that concerened with MSM resonance frequency specifically, rather,
I want to incorperate GG in lightweight walls in various, sometimes multi-layered non-standard applications.
as you know, nothing beats raw field test data, especially in special applications.
my feeling is that going from 2 layered drywall with GG to multi layered with intermediate GG would give better trend than just going with mass, cavity etc, though you would know better.
if we had data for even one test-application of multilayered multi GG, that could give a trend, but I could'nt base all on the exisiting data.
what I mean is to know how to use GG as a "building block" , not just as one pre-set application.
example: project where a large area dividing wall between 2 music functions, must be non-massive, only drywall, lots of LF, so needs exra high TL, yet not worried about specific MSM cause I could always EQ narrow freqs out later.

thanks,
Ido
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Re: Another Green Glue Question

Postby seb » Thu Sep 09, 2010 2:13 pm

Well, I have some sort of positive progress. I have piggybacked a test onto someone else's test series in a full size acoustic lab. For reasons I won't go into here, these are the tests that I have been able to fit in:

* 2x6mm plasterboard on one side of steel studs;
* 2x6mm plasterboard on one side of steel studs, with Green Glue.

The Green Glue panels have already been made and have been laid flat and weighted down. Each panel is 3.6x1.2m and includes 3 tubes of Green Glue. To help the sheets bond there are 20 or so 20kg bags of plaster on top of each panel while the GG cures.

The above walls are not quite studio walls, but they have the merit of being half of a studio wall, or shall we say, half of a double-stud wall. Yes, they are 6mm plasterboard, not 16mm. That is the best I could do (I would have preferred at least 13mm) but still it should tell me what I want to know about GG. The test series is scheduled for 4 weeks or so after the panels were made, so the end of the month should do it.

The lab is full size, with 200m^3 rooms and 10m^2 test opening. Flanking is somewhere well over Rw/STC 84. The test opening is 3.45m tall x 2.90m wide. It is taller than it is wide. The stud frame will be 92mm light-gauge steel studs at 600mm centres.
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Re: Another Green Glue Question

Postby seb » Fri Oct 01, 2010 10:28 pm

At last I have a test result to report. Please see the graph. One of these walls is not like the other wall...

Clipboard01.png
Clipboard01.png (6.67 KiB) Viewed 5172 times


Remember that this is a single row of studs clad one side only with two layers of plasterboard. It is exactly half of a double stud wall. It shows no benefit from Green Glue at low frequency. This is unlike the single stud tests published on the Green Glue web site, with the wall frames clad both sides, which show significant improvement from Green Glue at low frequency.

The website test results show that Green Glue works very well for certain types of walls, the implication being those where stud-borne transmission of acoustic energy affects the TL of the wall. For walls where stud-borne transmission is not an issue, this recent test result would suggest that Green Glue only helps in the coincidence region of the plasterboard. I suppose there could also be benefits from Green Glue in cases where there is an issue of transmission from the wall leaf into the surrounding structure. However, that is a different test scenario and a bit harder to quantify as it would require a full scale mock-up of a room. In cases of floating construction - which I suppose would be many professional and even some home studios - then this recent test result suggests there would be no benefit from Green Glue except in the coincidence region.
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Re: Another Green Glue Question

Postby Scott R. Foster » Sat Oct 02, 2010 2:13 am

Very interesting - and contrary to what I would have guessed - thanks for sharing.
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Re: Another Green Glue Question

Postby bert stoltenborg » Sat Oct 02, 2010 10:02 am

I never trusted that Brian....
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