The Drum Bubble - Material to use between wall and floor

Ekimtoor1

Member
I’ve had several suggestions to use a resilient material under the wall between the wall plate and the floor.

My floor is a concrete slab and in my reading, information about how a concrete slab transmits sound is all over the map. Or I’m not understanding what I’m reading.

I need to decide now before I go any further with my build whether to bother with putting something under the wall or not, and what improvement I could expect from doing so.

Can you help?

Thanks
Mike
 

rob aylestone

Well-known member
The reality is a fairly simple one. materials that remain non-rigid offer isolation. So the resilient strips, the neoprene those rubbery gizmos under floors the seals on doors and of course the dreaded green glue do offer something. The only question of course is how much? The formulation of the different types relates to the residual weight. A timber stud wall, with layers of sheet material, plus the weight of the ceiling is a substantial amount, so the normal neoprene used has to be able to not deform completely with this weight. This suggests it's rigidity is higher than the neoprene used around a door seal for instance. Any decoupling is better than no decoupling at all, but it's not going to make huge differences. All the decoupling on wall to floor, wall to sheet, sheet to sheet etc has a cost and a measure of how well it works. So many are unable to be quantified. Logic says that there will be a difference, just because of the science, but actual amounts? Nobody ever builds a room then measures it's performance then starts again with a different technique? I've got a pretty decent viewpoint after many builds and they're always compromises. For me - never, ever green glue again. Too much mess and expense and no apparent difference to similar rooms without it. Neoprene between floor and timber is an every time technique because it's cheap and simple. I cannot say if it makes a huge amount of difference, but the impression has always been it works and is also good at preventing gaps where the concrete and timber joint might be slightly less a good seal.
 

Ekimtoor1

Member
The reality is a fairly simple one. materials that remain non-rigid offer isolation. So the resilient strips, the neoprene those rubbery gizmos under floors the seals on doors and of course the dreaded green glue do offer something. The only question of course is how much? The formulation of the different types relates to the residual weight. A timber stud wall, with layers of sheet material, plus the weight of the ceiling is a substantial amount, so the normal neoprene used has to be able to not deform completely with this weight. This suggests it's rigidity is higher than the neoprene used around a door seal for instance. Any decoupling is better than no decoupling at all, but it's not going to make huge differences. All the decoupling on wall to floor, wall to sheet, sheet to sheet etc has a cost and a measure of how well it works. So many are unable to be quantified. Logic says that there will be a difference, just because of the science, but actual amounts? Nobody ever builds a room then measures it's performance then starts again with a different technique? I've got a pretty decent viewpoint after many builds and they're always compromises. For me - never, ever green glue again. Too much mess and expense and no apparent difference to similar rooms without it. Neoprene between floor and timber is an every time technique because it's cheap and simple. I cannot say if it makes a huge amount of difference, but the impression has always been it works and is also good at preventing gaps where the concrete and timber joint might be slightly less a good seal.
Thanks, Rob.

Below is the best data I’ve found so far suggesting that using a resilient layer between floor and sill plate could be worth 10 STC points. I think that’s significant? Green Glue claims 12.

I just don’t know if that is enough gain to justify what I have to do to get the seal in there. The only leak I’m chasing is low frequency bleed or resonance into the adjoining BR. If I could be sure I would get something, I’d do it. Seems like a blind effort.

I am in a rather unique position to measure before and after the seal install.

 
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Slouching Raymond

Well-known member
Take a look at the thick rubber sheets that are layed on children's outdoor play areas.
You could cut them into strips. They are about 1" thick, and would not squash.
 

rob aylestone

Well-known member
This is the snag with all things acoustic. They’re one shot builds.

when I built studio number 3. A big one in a college in the late 90s. I changed things because the design of 1 and 2 got spoiled by students. Gypsum based sheeting is the standard. We all use it, but it is fragile, easy to damage and very quick to look tatty. Students with office type chairs ran horizontal gouges where they fidgeted, and flight cases destroyed corners and falling mic stands and cymbal stands would make big dents. So in version 3, which would be a very busy one, I had two layers of plasterboard, with a layer of insulation board between them. Not sure if this is a UK term, but the stuff you use on notice boards, the. On the inner surface 18mm of MDF. This meant we could screw shelves, racks, treatment and guitar hangers directly to it, anywhere. Banging in with knuckles produced just a single ’duh’, no hollow sound. Sound leakage was impossible to detect through it, because it was clear the weakest link was the door. My mistake was using available data on sliding patio style doors. Good quality heavy duty ones with excellent heat data values but no data for audio. The actual glass was heavy duty float glass with decent gap, but the frames were the weak point. I chose mahogany but did not realise they were hollow, to break the heat path between hot and cold. They let sound through. Not badly, and perfectly usable just not as good as the walls. It did 20 years and still looked pretty good inside. The MDF I have repeated nearly every time since the, replacing one plasterboard layer with it on the inside. It makes a room within a room much stronger as it is rigid.
 

jamesperrett

Active member
...So in version 3, which would be a very busy one, I had two layers of plasterboard, with a layer of insulation board between them. Not sure if this is a UK term, but the stuff you use on notice boards, the. On the inner surface 18mm of MDF. This meant we could screw shelves, racks, treatment and guitar hangers directly to it, anywhere. Banging in with knuckles produced just a single ’duh’, no hollow sound.
This sounds slightly similar to the BBC's Camden Partition design although in their case they use the fibreboard next to the studs and have 2 layers of plasterboard together. I had this in my last but one studio with a further layer of rockwool covered by pegboard and then fabric.
 

rob aylestone

Well-known member
I just don't know if the insulation board actually does anything? I wonder if it's just like green glue? You can prove the science, but with theory and factual data but not in any real way that a listener could determine. I suppose you could seal off the end of a room with studwork, and the line it with sheet material, and do a wide ban analysis of what gets through, then remove the outer layer, apply green glue and put back together. That's a perfectly straightforward practical test - but I have never heard anyone actually do it? I wonder why?
 

Ekimtoor1

Member
I just don't know if the insulation board actually does anything? I wonder if it's just like green glue? You can prove the science, but with theory and factual data but not in any real way that a listener could determine. I suppose you could seal off the end of a room with studwork, and the line it with sheet material, and do a wide ban analysis of what gets through, then remove the outer layer, apply green glue and put back together. That's a perfectly straightforward practical test - but I have never heard anyone actually do it? I wonder why?
Green glue publishes such data on their website, for whatever it’s worth. To me, as an amateur, it seemed credible and I decided to use it. But as you have said, it’s really messy and although GG claims to block low frequencies better than other solutions, I have loads of low frequency transmission.

I’m about to install a sill plate isolation material. I have some measurements as is with the framing sitting directly on the slab. It will be very interesting to see the results of the same tests after I put the seal in. I’m hoping for a low frequency transmission reduction.
 

rob aylestone

Well-known member
This is why I'm just sceptical on the GG specs - on paper they look good but is your low frequency issue the glue not that effective or something else. You can't remove it to try. Just one YouTube video of a room without it, then with it would be so good, but all you get are specs with no context.
 

jamesperrett

Active member
I just don't know if the insulation board actually does anything? I wonder if it's just like green glue? You can prove the science, but with theory and factual data but not in any real way that a listener could determine. I suppose you could seal off the end of a room with studwork, and the line it with sheet material, and do a wide ban analysis of what gets through, then remove the outer layer, apply green glue and put back together. That's a perfectly straightforward practical test - but I have never heard anyone actually do it? I wonder why?

The BBC have done the testing - here are some examples.

This one explains the various Camden designs


while this one shows that there may be more modern alternatives that are better at mid frequencies although the Camden still seems better at low frequencies


It is well worth exploring the BBC R&D website if you are thinking of building a studio.
 

rob aylestone

Well-known member
Interesting stuff. I wish they’d tested green glue though. I did not know the fibreboard was so good. That’s one to remember. Thanks for that info.
 
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