My experience with Green Glue

[jazzman_in_pa]

Hi guys. We finally put up our control room ceiling, which consists of 2 sheets of 5/8" sheetrock and a layer of Green Glue between them as prescribed (troweled on with a notched trowel). The sheetrock is hanging from hat track which is hanging from C-channel which is hanging from Kinetics ICW-100 isolation hangers. A gap of around 3/16" at the ceiling perimeter is filled with OSI SC-175 acoustical sealant.

So what do I think of the results?

I am totally impressed with the damping characteristic of the Green Glue.

It's an excellent product and at 80 cents a square foot is worth the money, specifically for its ability to drastically reduce the "ringing" of the sheetrock ceiling to inaudible. This ceiling will not be storing and sending LF energy back into the room to muddy up the sound. By comparison, I've got one half of a double wall up, with 2x4 studs spaced 16" o.c., 3/4" MDF + 1/8" MLV + 5/8" sheetrock. I built this wall partition before hearing of GG.

Bang on the wall between the stud screws with the meat of your hand, and you hear some low frequency ringing. Bang on a section of ceiling and you hear--no ringing at all. It's just like all those graphs on Audio Alloy's website. The difference is dramatic. So dramatic that I've already decided to add another layer of 1/2" gyp to these walls with GG this time.

Disclaimer: I have no personal interest in Audio Alloy (other than to enjoy Brian's constructive repartee on this forum).

2nd disclaimer:

• put plastic sheeting on the floor first,
  a baseball cap on your head,
  vinyl gloves on your hands, and
  keep a warm bucket of soapy water and plenty of paper towels nearby.

This stuff is stick-eeeee. Put blue masking tape on any tools you'll be handling a lot. You'll be glad you did.

Lee

[eric_desart]

Lee,

First:

I do believe your description for 10000 %.
I do believe, and have seen the measurements in function of thodse extreme CLD damping values.
I know and recognize the intelligence, knowledge and honesty of Brian, the guy behind the Green Glue.
I certainly do believe that it has real valid applications.

Second:

What I also see is the typical audio/studio group approach.

You compare this ringing of the ceiling with this wall combination. And again I do believe you're experience to be true.

My question is VERY dry.
What does this so-called ringing means in practical circumstances in a studio.
In other words what is the real practical added value?

Basically I know the physical phenomenon is true.
But that's as if someone is proving that he can get rid of the coincidence phenomenon for 100 %, knowing the excistance hardly matters in a practical applications.

What I really want to see quantified is the real practical gain versus cost.

Your experience I'm very grateful for and is very important.
But towards laymen it also includes question marks and can cause confusion for me.

You describe something which is true, no doubt about it.
It sounds as it's the only future way to go.
But nowhere I can see what the real practical gain should have been versus traditional solutions which comparable or even lower cost.

I NEVER, repeat NEVER heard anyone telling that the ringing of your wall combination caused ANY practical limitation or problem whatsoever.

• So you improve what?
  A problem?
  A physical phenomenon?

Now I'm certain that the green glue will beat the hell out of the MVL. And versus MVL certainly it's very cost effective.

But I still wonder if the MVL was needed at all?

I still want real measurement data were it is possible for people to judge cost versus real practical gain.

That Green Glue is perfect, I don't doubt for one single moment, and I even hope to use it myself some time.

But show me the messages here or at JS where a standard GOOD build typical studio wall caused trouble due to ringing.
You describe it as you found the solution for a problem.
But nothing shows that problem is a problem at all.
That problem is only a problem with very low insulation values, and very low damping causing the reverb time of this ringing you pin point to be longer than the reverb time of the room itself.
Otherwise you're just describing a theoretical phenomenon.
And don't take AVS as example. I've read more things there causing me to wonder.

And I know increased damping improves TL.
That's what I want to see. To check real advantages versus cost.
I can imagine the drumskin effect of a floating floor being very well served by Green glue.

Your experience however, for me is plain physical without telling anything about the practical gain.
And that it should sound dead as hell, seeing Brian's measurements, which I know Brian as a physical honest technical maniac should never falsify, I knew without your ceiling too.

Don't read me wrong: I believe in Green Glue and even more in Brian.
And you have the right to be proud, and your ceiling is certainly the maximum you could get out of it. And I'm grateful for sharing this experience.
The simple question remains: how much more was this translated in more practical terms?


I edited this somewhat

[z60611]

I thought the big advantage of Green Glue was that it reduced resonance by damping vibrations, and thus improved TL especially at the dips.

The observation by jazzman_in_pa implies that field use of green glue does do damping, therefore it's likely that it'll improve TL.

As for in-the-room-acoustics there have always been four posibilities
1) the resonance of the walls could absorb sound at that resonance creating a dead frequency
2) the resonance of the walls could ring sound at that resonance creating a tone at that frequency (in the HT world that would be hearing a tone instead of a cannon)
3) some combination of a + b
4) none of the above.

Have there been any studies on membrane traps about 1/2/3/4 ?
It seems to me that it would be easier to do a/b testing on portable membrane traps vs an empty room, than removing a layer of unglued drywall and then adding a green glued layer.

Of course I'm assuming that a wall is a massive (heavy) and large-surface-area unpredictable peak-frequency(s) and unpredictable-Q membrane trap, and that a study of portable membrane traps might be applicable to walls, vis-a-vis in-the-room acoustics.

[eric_desart]

Z,

I should find it certainly interesting to have more in-depth research.
By definition or at least mostly damping is good.

I think that a complete green glue room feels very solid by this phenomenon, and therewith psychologically feels very sound.
So I certainly can imagine Lee's enthousiasm.

If I compare this with the industry were numerous acoustic enclosures are build from steel.
When not damped and knocking on it it feels cheap and unprofessional.
When damped such an enclosure feels much more solid, acoustical (whatever that means in this context) and more expensive (those layers don't cost that much at all).

When we measure the increased TL with and without, the practical difference, certainly when subtracting the added mass is in fact minor.
Still one standard applies it as a quality measure and the increased mass where needed without being forced to make the whole enclosure of thicker steel.

Now this is no real CLD as Brian describes.
I just want to know, what is the psychological part and what's the real part.
And finally the cost and energy effectiveness versus more standard solutions of comparable, even lower cost.

But towards Brian:
With what I know now, or think to know, if I should choose for damping Green Glue should be my first choice.

I just want better data to decide when and where and if.

[Rod Gervais]

OK,

I like Brian - and I too believe he's a straight shooter.

But Lee,

Part of what you describe can be attributed to the difference between a floating ceiling assembly and a stiff wall assembly.

The 2 have totally different panel characteristics.

So even if you didn't have the green glue - the ceiling would have a different sound effect than the wall.

That having been said -

I'm with Eric - I think the product is a good product - the real question though is this -

EXACTLY what is my gain for the added cost - and how would that compare with say an additional sheet of 5/8" drywall from a benefit/cost point of view.

The ringing you refer to when slapping your palm on the wall is not an issue unless the people recording in your studio are making their music by slapping the wall...........

I've built some nice studios - some absolutely world class studios - and have never used this product (or any like it) for construction purposes - and have also never had a problem with walls ringing.

SO what exactly is it that is going to entice me to tell my clients that this green glue is something they should spend their money on?

Because before I tell them to do it - I have to believe in my heart of hearts that this not only works (that's the easy part) but that it works less expensively than I can acheive with other means.

If I can get exactly the same results and save my client 50 grand on their budget - why wouldn't I take that path?

BTW - this is the same reason I tell people to avoid using the specialty drywall boards on the market - it isn't because they don't work - THEY DO........... it's because I can take them to the same place for a whole heck of a lot of less money by using traditional methods and materials.

So again - what is the true bang for the buck here?

Sincerely,

Rod

[AndrewSteel]

Hi everyone,

Z's question is a great one for me - could someone please answer the 1/2/3/4 scenario he presents? Does wall resonance mean absorption or does it cause reflection etc

Andrew

[z60611]

Rod

EXACTLY what is my gain for the added cost - and how would that compare with say an additional sheet of 5/8" drywall from a benefit/cost point of view.
...
If I can get exactly the same results and save my client 50 grand on their budget - why wouldn't I take that path?

Admittidly we're all still awaiting good lab testing results from Brian/AudioAlloy.


Nevertheless you might want to glance through this poor thread
http://www.avsforum.com/avs-vb/showthread.php?t=542604
where BasementBob took at stab at some ahem comparisons of AudioAlloy's results vs ir761 (and a bit about MLV and a few other things)

Here's a tidbit from that thread:

Green Glue Coverage: (approx, results will vary) 60 sq. ft. per gallon
Packaged: 5 gallon pails
Cost per square foot: $0.75
Cost per 5 gallon pail: $225

An 4'x8' sheet of 1/2" drywall is about $15CDN, or about 0.45 cents per foot.

In this thread Brian Ravnaas writes,

there is 3rd party data from NVLAP labs for a 2x4 wall assembly (STC 56, 24/25 dB of TL at the low frequency resonance point, relatively superb performance compared to alternate options), and for a double stud wall (32/36/35 dB of TL at 40/50/63hz, as far as i know the best stud wall ever tested)

from IR761

2G16_SS65(610)_GFB65_AIR20_SS65(610)_GFB65_2G16
50hz 16.0 dB
63hz 22.8 dB

2G16_SS40(610)_MFB40_AIR65_SS40(610)_MFB40_2G16
50hz 18.1 dB
63hz 24.0 dB

2G16_SS40(610)_MFB40_AIR65_SS40(610)_MFB40_2G16
50hz 23.7 dB
63hz 27.9 dB

2G16_WS90(610)_GFB90_AIR25_WS90(610)_GFB90_2G16
50hz 26.7 dB
63hz 31.8 dB

2G16_WS90(610)_AIR25_WS90(610)_CFS60_2G16
50hz 30.0 dB
63hz 21.0 dB

Not one of those gets near the GG's advertised
50hz 36.0 dB
63hz 35.0 dB


So, just for the sake of a bit of math, let's say that that GG improves the 50hz to 63hz performance by 6db, using the bold lines I compared above. (Alternatively we could say that GG improved the performance by 10dB using a different pair, but then I'd claim that we should use the 10dB difference in doubling mass that I found below -- so let's continue comparing apples to oranges and just go with it)

To use GG you have to have two layers of gypsum on at least one side, but for this example lets say you have two layers of gypsum on both sides.

To get a 6dB increase in performance using drywall/gypsum alone, you have to double the mass. So we'd have to buy 4 more sheets of gypsum, spending $0.45 per foot * 4 = $1.80 per foot. Here I think the 6dB improvement is from 20hz to 20000hz, but a little less at the resonance point around 45hz.

The 6dB by doubling the mass is just a rule of thumb. Sometimes it's higher sometimes it's lower. Here I'll take one wall, and double it's mass, just as an example, and it looks like it's about a 10dB improvement from 50hz to 200hz:

G16_WS90(610)_GFB90_AIR25_WS90(610)_GFB90_G16
50hz 15.6 dB
63hz 19.9 dB
200hz 46.5 dB
1khz 76.9 dB
5khz 86.4 dB

2G16_WS90(610)_GFB90_AIR25_WS90(610)_GFB90_2G16
50hz 26.7 dB
63hz 31.8 dB
200hz 55.9 dB
1khz 81.5 dB
5khz 91.5 dB

There are other examples where it's much less than 6dB.

But since we're just playing around with numbers and math, I'll ignore the higher and lower examples, assume the 6dB for doubling the mass, and keep typing.


To get a 6db increase in performance with GG, we'd spend $1.50 per foot (2 * $0.75). Here I think the 6dB improvement is mostly around the resonance point around 45hz, but a bit of improvement at the other frequencies as well.

Generally speaking, we have plenty of isolation at the higher frequencies (500hz to 20000hz), so we don't really care what happens there.

My conclusion, for less money ($1.50 GG vs $1.80 for 4 more drywall layers), you get more improvement (6dB vs something less than 6dB) at the frequencies you are concerned with, by buying Green Glue over doubling up on the drywall.

[eric_desart]

Bob,

Do you have those TL values per freq. somewhere in an Excel Table that you could Email me?

I just want to do some easy calculations and post results here.

If not asked too much give those measurements numbers with descriptions rather than those Chinese NRC codes (I know they tell it all very correctly, but are unreadable if one isn't familiar with them)

TIA

Don't use the local options here, I'm not registered.
:twisted: Have a principle problem with paying to help.

[z60611]

eric_desart:
I'm unsure what you're looking for.
Nevertheless I've emailed you some data.

2G16 is two layers of 16mm gypsum
SS65(610) is steel studs 65mm deep on 610mm centers
GFB65 is 65mm of glass fiber batts.
AIR20 is 20mm of air.
MFB40 is mineral fiber batts 40mm deeo
WS90(610) is 2x4 wood studs 90mm deep on 610mm centers

[Brian R]

Hi Lee, i am terribly happy that you're pleased with your results. and hopefully the cartridges/tubes will be alot less messy.

Hi everyone,

Z's question is a great one for me - could someone please answer the 1/2/3/4 scenario he presents? Does wall resonance mean absorption or does it cause reflection etc

Andrew

hi andrew, i entered some recent data on the absorption of some walls relative to concrete, various explanations of data are present in that thread. here's a link:

http://forum.studiotips.com/viewtopi...=1559&start=20

Brian