Sorry I hadn't spotted the rules thread...I've now had a read and will adhere!
So we're talking 60-70dB max I think.
That would be classified as very high isolation, far beyond what most home studios achieve, even when very carefully designed and built. An excellently designed studio that is very carefully built with great attention to detail might get 60-and-a-bit dB of isolation. I'm not aware of any home studio that has achieved over 70 dB of isolation: that would require a budget and construction techniques well beyond what that average home studio owner could afford. A typical home studio on a decent budget might get 50-something dB of isolation, if done with reasonable care. Most get in the region of 40 to 50.
So I very much doubt you'd get 70 dB, or even 60, with the techniques, methods and materials you are using. I would hazard a guess and say maybe 40 or so. That's assuming you use the correct isolation mounts for your ceiling. Without that, you are down into the 30's, along with most other fully-coupled walls and ceilings.
All we are really trying to achieve is minimizing the transmission of normal TV noise and say 'normal-to-loud conversation' between the floors.
so you don't have a problem with the sound of footsteps on the upstairs floor, doors opening and closing, vacuum cleaner running, telephone ringing, washing machine, water running in pipes, rain, hail ,wind, thunder, aircraft flying overhead, lawnmowers outside, dogs barking, street traffic, etc? With fully-coupled flooring, the usual biggest issue is impact noises (walking, running, things dropped, doors closing) and other structure-borne sound.
I follow what you are saying and any of your suggestions sound ideal, but unfortunately I really am in a predicament where we must proceed with the drywalling,
If you really cannot find the time and money to replace the faulty isolation system with one of the others that I mentioned, then yes, you really are in a predicament! The only choice you have is to live with the limited isolation provided by a fully-coupled floor/ceiling system. There are no alternatives.
forge ahead without any acoustic isolation at all (which I am seriously considering)
That probably is your only choice. Why is it that you cannot scrap the system that is incomplete and replace it with one of the many other systems that I mentioned? You do have several options there. You also do have the option of not putting up the ceiling yet: just complete all the other drywalling, on the walls and in the other rooms, then leave this one until the end, after the parts arrive. It's not that hard to put up some drywall on a ceiling yourself, then mud, tape, and paint it. A good weekend project for a couple of people. Would it really be that bad to have the rest of the house finished, but not the downstairs ceiling?
or improvise something with what is at hand.
Unless you have a really good grasp of the physics and mechanics of the solution you improvise, in terms of being able to do the math and calculate the outcome, then there is little point to even trying. Learning how to do that would take as long as the shipment of the missing parts, and more. There's an awful lot of detail that goes into a resilient isolation system.
If we forego acoustic isolation, this would mean relying only on bulk insulation in between the joists, and two layers of drywall attached to the ceiling either directly to the joists or via battens/straps
That is basically a typical fully-coupled 2-leaf ceiling. You could expect isolation in the mid 30's from that. Mounting it properly on good resilient mounts would make it about ten times better, in the mid 40's, all other factors being equal.
(although without any rubber isolation mounts I can't imagine that the battens/straps would have any benefit at all over simply fixing the drywall directly to the joists)
Their might be some minor effect from that, since it looks like rather thin metal, but it's certainly not going to make a huge difference.
Is this likely to be remotely satisfactory given our objective?
Depends on what your objective is:
If your objective really is to get 70 db Of isolation, then no, very definitely not! You'd need a major re-design and re-build to do that. If your original objective is to get into the mid 50's of isolation, which is typically what you find in a well designed/well built home studio, then no: you are still short, as you will only blocking about 1/100th of the energy that you'd need to block to get there. If your objective is to get about the same as any typical house situation, then yes, you would achieve that, and maybe even get slightly better than that, due to the extra layer of drywall (which in theory should buy you an extra couple of dB).
I wish I had better news for you, but that's the sad facts of reality. Using a layer of Green Glue CLD compound in between the two layers of drywall would help a bit, maybe adding another couple of dB, but to be honest, unless you can properly deco9uple the two sides of the barrier (floor from ceiling), then you won't get good results. The laws of physics are against you on that one, unfortunately.
- Stuart -
