Acoustic Board as Apposed to Gypsum (spec included)

Hey everyone, So I'm researching materials to fix my studio walls and I found this product available here in south africa. It looks good but thought Id get your opinions. http://www.genesisacoustics.co.za/downl ... _Apr12.pdf Currently the studio walls are just a straight forward steel frame drywall. 12.5mm gypsum - steel stud (with fiberglass insulation) - 12.5mm gypsum. What i plan to do, I cant alter the outside of the wall so I am going to remove the inside leaf of the walls of the studio. Leave a gap of 50mm and then construct a new framework for a second wall essentially creating a MSM where the inside leaf and ceiling is decoupled from the outside except for the concrete slab floor that the walls stand on. Will also fill the new inside wall leaf with fiberglass insulation (24kg) then i plan to finish the inside leaf like this. First layer -12.5mm gypsum, on top of that 9mm genesis acoustic board and then green glue and a second layer of 9mm genesis acoustic board. For the ceiling I will be using 2 layers of the genesis board with green glue in between. In between the live room and control room the leaf on both sides will be 1x gypsum - 1x genesis board - green glue - 1 x genesis board. I should get an STC of at least 70 and a tl of about 30 down as low as 80hz? What do you guys think? G

First layer -12.5mm gypsum, on top of that 9mm genesis acoustic board and then green glue and a second layer of 9mm genesis acoustic board.

I don't think I'd go with such thin materials. That "genesis board" is a bit more dense than drywall, but not by a lot. Around 20%, it seems. So look at prices: if that stuff is more than 20% more expensive than plain old fire-rated drywall, then forget it. Sound waves don't care how much you pay for your mass: they can't read price tags, and they aren't elitist anyway! :) They just react to the mass, so get the cheapest mass that will do the job. Also, the claims on that PDF document are a little suspect, since they aren't back up by any independent research lab test data. Maybe they do have real test data, but I didn't see it there, so that's something to think about. Also, they talk about STC rating, which is a pretty useless measurement for studios as it days nothing at all about low frequencies.

1x gypsum - 1x genesis board - green glue - 1 x genesis board. I should get an STC of at least 70

I doubt that you'd get anywhere near STC-70! What did you base that on? According to IR-761 there is no construction at all that will get you SC-70. The closest is STC-69, which was accomplished with two layers of 16mm type X drywall, separated by a 205 mm cavity filled with two layers of 90mm fiberglass insulation, using 2x4 studs 24" OC. Next closest was STC-67, which was the same as above but with the studs at 16" OC. Building an STC-70 wall is no easy task. In any event, even if you did manage to build an STC-70 wall, that would be overkill since the floor, doors, windows, ceiling, HVAC and electrical system would not get you the same level. The room is a system, and the total isolation is only as good as the weakest link.

and a tl of about 30 down as low as 80hz?

Perhaps, but that depends on other factors. - Stuart -

Hey Stuart, Thanks for the reply. I agree that there are really not any propper test results on the genesis boards. This is probly what prompted me to start posting about it on here in the first place. When you say they are about 20% denser than normal drywall board do you mean the 15mm fireboard? So a 9mm genesis board is 20% denser than a 15mm drywall board? But then what about the thickness difference? Cost wise a 9mm genesis board is about 20% more expensive than a 15mm gypsum. I based my assumption of 70stc on figures from green glue (double stud construction UL# U347) but your absolutely right, we won't get it so high right across the board. If we can get the system anywhere above 60 I'm pretty happy with that. My concerns are only building noise and outside street noise getting into the studio, as you know I'm not bothered with what gets out. I just want my recording and mixing environment to be as quiet as I can possibly get it. I'm allso still looking into cement fibre board options as well. G

Hey, After doing some research it appears that these magical genesis boards are nothing more than standard Magnesium Oxide Board. Two phone calls and I've allready found it cheaper elsewhere, more than likely cheaper due to the fact that it doesn't have acoustic in its name and isn't sold by an acoustic solutions company. Apparently a wall with a single layer of 9mm magnesium oxide boards on either side is equivalent to a wall with two layers of gypsum fire board on either side. A magnesium oxide board has an STC rating of 54. Still waiting for data from suppliers to see how they perform on the low end. But still sounds pretty good. I'm thinking of using these with green glue for my walls and ceilings then. Anyone have experience with them or any other thoughts? G

When you say they are about 20% denser than normal drywall board do you mean the 15mm fireboard? So a 9mm genesis board is 20% denser than a 15mm drywall board? But then what about the thickness difference? Cost wise a 9mm genesis board is about 20% more expensive than a 15mm gypsum.

Not really. I was referring to the true density, not the surface density. The true density of good fire-rated drywall is about 750 kg/m3 (depending on manufacturer), while the advertised density of this Genesis stuff is around 900 kg/m3. That is regardless of thickness. Sure, a thicker panel will be heavier, but the density will still be the same.

A magnesium oxide board has an STC rating of 54.

Once again, that depends entirely on how the wall is built! Paper can have an STC rating of 54 if you build the wall suitably, while even concrete won't get to STC-30 if you build it wrong. I always get concerned when I see manufacturers claiming that their product alone has an STC rating of such-and-such, or that it reduces sound by 80%, since those are both entirely meaningless and useless tidbits of information. Unless they state how the wall was built, and how it was tested, then the claims mean nothing at all. That's why it is so important to only use products that have been tested in independent acoustic laboratories, with the full results being published and easily available. The lab will tell you exactly how the wall was built, exactly how it was tested, and exactly what the results were, with no vested interest. If the manufacturer doesn't provide such data, then the product is suspect.

I'm thinking of using these with green glue for my walls and ceilings then. Anyone have experience with them or any other thoughts?

My concern would be with how thin they are. At just 9mm I would expect them to be very flexible and also to have a high resonant frequency, neither of which is good, regardless of density. At higher frequencies, mass law rules, but at lower frequencies it is rigidity that governs isolation, so thin flexible panels don't do well at low frequencies, even if they are very dense. Limp mass works well at low frequencies, but the panels you are talking about are not limp mass. - Stuart -

Hey Stuart, Ok I see what you mean. I just received the price lists for these boards and they aren't bad at all. Also after doing some googling it seems that they are quite the craze in the world of dry wall construction. Some might even say they are the future of dry wall construction and one day will be the norm over gypsum. This of course will always be a question of economics but in today's terms they are a superior product to gypsum by the looks of it and for almost the same price. After looking at the price list it shows that the magnesium boards come in thicknesses of up to 20mm. So I'm looking into the 15mm for the studio. Since the density is higher as it is I would imagine that using these in 15mm thickness (for rigidity as you say) should be a better wall than using 15mm gypsum. So the plan for now (still have to crunch the financial numbers) 12.5mm gypsum - 15mm magnesium board - green glue - 15mm magnesium board. I am waiting for the supplier to send me a copy of some lab tests that were done on the magnesium boards from their manufacturer. I did look into fiber cement boards but they just wont fit the budget as they are 3 or more x the cost of gypsum board. I understand that it is all dependent on how the wall is built. In my case you know pretty much how I will be building the walls from the sketchup model in my other post. As far as sealing up is concerned I will use a non hardening caulk on the under layers and use green glue sealant on the front layer on every join top to bottom. My biggest concern is the glass between the LR and CR but purely because it will limit how high I can push the monitors while tracking. Besides that relatively small issue the only thing I care about is keeping the worlds noise out of that live room. The brochure for the boards from my local supplier can be viewed here: http://www.magnastruct.com/7498_brochur ... ochure.pdf If your interested in giving it a read. I don't believe this is a suspect product at all, I think it is just a relatively new one. But my research continues. As soon as I come across some lab test data I will post it up right away. G

Fermacell panels (if available where you live) are ca. 1200 Kg/m³. A 15mm thickness weighs 18 kg/m² compared to normal drywall (data from Knauf) which has a weight of 12.2 kg/m² for an 18mm thickness (14.4 for 18mm special firewall).