John Sayers' Recording Studio Design Forum Archive

maybe not on the brick but you have windows which may need reduction in size to improve isolation (example - frame + drywall to reduce it then a newer interior "storm" window to improve that, etc). you need to do some testing with loud volume PA to assess existing isolation and weak points.
definitely peek behind the t&g and document the structure there. this would be a good time to consider blowing in insulation if there isn't any.

Hi Glenn, interesting, I hadn't heard about that technique anywhere yet- does adding a storm window in front of the existing window, plus the inner room not create the dreaded three-leaf system though? I'm also a bit worried about having to make the inner room smaller to allow for the required frame and drywall. Also, thanks for the point on ceiling insulation.

Meanwhile, I've received a report from the engineer, the key sentence being:

The current use of the unit is office usage, so without checking the steel beams or spans, the minimum floor loading can be assumed to be 2.5kN/m2 as per BS 6399: minimum imposed floor loads Part 1

Now, I have some problems with this- why didn't they check the beams then? Also, reading the abstract of BS 6399, it doesn't necessarily apply to old buildings like this one, so might be meaningless anyway. I've followed up with them.

For argument's sake, if this value did happen to be true, that would allow for loading the room evenly with 6,300kg. My initial calculations of additional weight however, after replacing the wooden floor with concrete, floating a new concrete slab resiliently on top of it, and using two layers of acoustic plasterboard for the inner walls and ceiling, are close to 9,200kg, if, say, 50mm concrete are needed to level the floor, and a 100mm floating slab were poured. As you said, this mass would not be evenly distributed either.

What is the minimum slab thickness of reinforced concrete I could float successfully? Does the weight of the slab alone matter, or the combined weight of slab and walls? Maybe a bit of both?

The other acoustician I mentioned recommended contructing a floor out of playwood, filled with sand. What do people here think about that? Sand appears to have about 2/3 the density of concrete.

At the risk of , I do also need to follow up and ask if anyone here might be able to answer my last post's questions.

a sand filled floor is heavily damped but not necessarily floated. a floated sand floor will have similar weight distribution as a concrete one. a minimum (imho) is 4" (100mm) steel reinforced concrete floor. perhaps this begs the question - long term investment and who else is in the building that would be impacting you, or you impacting them? if this was a short term investment, maybe you can consider other means of decoupling which will not be as costly but might be sufficient? if there is no one creating significant noise or who might be affected by sound from you, again, maybe some other options might be considered.

the glass inside would be better, esp if you ever move and want to take it with you, less wear and tear on it. plus, you'd be adding another one on the inner wall (we're mass matching so 3rd leaf would not be an issue, esp since the outer window is likely thin).

for "floating", Kinetics Noise makes a roll out pad + insulation product which could be layers with (say) 3x 25mm plywood, mdf, or osb + finish. use heavier product on edges for walls. partly suspend inner ceiling and partly rest on walls. not going to be the same as a full floated space but may be enough.