Concrete or gyp board?

[Crispy]

I have a building with existing exterior walls constructed of 9" solid brickwork (no cavity). If I build the inner walls of both my control room (23'Lx16'Wx10'H) and live room (similar size to CR) with 4" dense concrete blocks (solid - not the types with the holes running through) I will only be able to afford a 2" air gap between the inner and outer wall. If instead I use wood or metal framing and 3 sheets of gyp for the inner walls, I could increase the air gap to 7". The reason for this is that there are brick pillars standing out from the existing walls which I could frame around using a stud wall but not a concrete block wall. So the question is: bigger air gap with gyp wall or better rigidity with concrete blocks? My primary requirement is sound insulation both from and to the outside world. Live room will be used for drums, loud amps etc. Ceilings will be several sheets of gyp, supported on inner walls, decoupled from the roof with plenty of fibreglass up there. I would be very grateful for some expert opinions.

Chris.

[Deluks]

I'd go with 4x2's and plasterboard, if you have 9 inch solid walls as an outer then that's a great start, assuming there are no airgaps or weakspots (windows? ventilation?) It will also work out cheaper I would imagine, framing is a diy job, brickwork can be DIY but the results may not be top notch.

The rest of your plan is sound, I'd maybe post more detailed info though, maybe with a few pics so as some of the experts on here can point out any potential flaws.

So whereabouts in London are you, out of interest?

Cheers
Del

[Crispy]

I think I'm leaning towards the plasterboard approach. Cheaper and DIY as you say. There are no airgaps or windows, just the access doors which will lead to other internal areas so the exterior shell is definitely a pretty good start. Once I've got some real plans together, I'll post 'em. Archway area of London for your info.

Cheers,
Chris

[knightfly]

Did some rough calcs on your scenario; with good seals and no hard contact between inner and outer walls, using 9" brick, 7" air gap and 3 layers 1/2" gyp you could end up with (maximum) STC 90, with a TL of about 52 dB @ 50 hZ and a mass-air-mass resonance of around 30 hZ - this would make it so drums at 105 dB would barely start to be audible outside, considering that the threshold of human hearing at 50 hZ is around 50-55 dB... Steve

[AVare]

Considering Steve's calculation results, three layers on the inside is overkill.

Andre

[knightfly]

Not necessarily, Andre; if good iso for live drums is needed, dropping one layer of gyp raises MSM by 7 hZ and lowers the low end TL by almost 3 dB. (These were 1/2" gyp I calculated)

This would raise "barely audible" to "noticeable", which might be a problem.

Also, the old Insul demo can be a bit optimistic, and is NOT FSTC AFAIK; so if I use it, I tend to choose MORE mass rather than less... Steve

[Crispy]

Thanks for the info. guys. Yes - 'noticeable' could well be a problem so I would probably play safe and put the 3 layers up. All being well, I'll own this building in a month or so. In the mean time I'll draw up some decent plans and see what the good people here think about them. Steve, is it easy for you to do the calculations on the masonry option described in the original post? If not then even an educated guess as to whether or not it would be more effective TL wise than the gyp method would be extremely useful to me.

Cheers,
Chris.

[AVare]

Thanks Steve. Chris has the data now to make, or to rewearch more in a definite direction the question.

[knightfly]

9" brick, 2" air gap, insulate, 4" concrete brick - assuming perfection again, STC 85, Tl is worst @ 90 hZ = 55 dB, mam resonance around 23 hZ... and hopefully you know a mason that won't drop even ONE glob of mortar between the two walls to ruin it.