John Sayers' Recording Studio Design Forum Archive

hi all -
I think I have been working too many hours getting this project done - stopped long enough to reread some posts here tonight and realized I may have a problem.

My walls are true double walls - 2X4 wood studs seperated by between 8 and 16 inches - filled with R19 fiberglass insulation. - Here's my concern - I have used RC on both of the walls (leafs) - if this is a problem can I just "short out" one of the walls (say the control room side) by screwing through the RC into the wood studs? - or do I have to remove the drywall and then remove the RC? - I am putting 5/8 then 1/2 then 5/8 drywall on each wall and ceiling. All seams are well caulked as well.

Thanks

Dan

Looks to me like you will lose about 5 dB or more at 50 hZ and over 13 dB STC by using RC. RC costs you low frequency performance when used in a wall (stiffer is better for LF) - in a true double framed, mass/air/mass wall, best performance is gotten WITHOUT using RC, period.

I don't have a way to calculate just how bad your existing way would be, but switching from RC to double studs in an 8" gap wall using the layers you mentioned, you gain around 13 dB - now, putting RC on the OTHER side ALSO, would "soften" the wall mounting there as well, resulting in even worse Low freq performance.

Whether you re-do one or both sides would depend on how much isolation you actually need, and how masochistic you are. The wall as is, would end up in the high 50's for STC, with around 32 dB TL at 50 hZ, increasing as frequency increases. Mass/air/mass resonance would be around 35 hZ, so the bottom 2-3 notes on a 5 or 6 string bass (and some kick drum fundamentals) would have less isolation than other instruments.

You haven't by any chance been shopping at a site called Supersoundproofing, have you? Those twits are the only place I've seen who are greedy/evil enough to recommend putting RC on both sides of a wall...

Bottom line - if you want/need max isolation, do it over. Leave out the RC, period - and make one of your two leaves different than the other one - use two 1/2" and one 5/8 on one side and the opposite amount of each on the other. IF you do it over on One side (no RC), you'll end up with at least STC 60-62, decreasing to around 33 dB loss at 50 hZ - if you redo BOTH sides, no RC on either, 3 layers each side, you'll be around 74 dB STC with 50 hZ coming in at around 38 dB. Leaving it as is will be worse than EITHER of the above scenarios, possibly by as much as 6-8 dB. BTW, these are all CALCULATED figures, NOT TESTED - field performance measurements would be a few dB worse in all cases, since nothing ever comes out perfect...

I don't think trying to "short out" your drywall and RC on one side would work - Trying to "suck down" all that drywall to collapse the RC would likely just make big holes in your drywall and worsen the problems.

God, I hate having to answer questions like this, I'd MUCH rather give you GOOD news - reminds me of the time several years ago when I built a custom 4 foot studio door from scratch, and then let in the hinges based on measurements I had taken with the door UPSIDE DOWN... Steve