2 ceiling questions

RC8 resilient channel can be used on ceilings I believe correct? But what I cannot find out is if I can hang ONE layer of 3/4" hardwood plywood from it? Is the plywood too rigid? I'm planning on attaching the RC8 on to 2x6 joists on the bottom of our house that is 12 ft in the air with a 2ft thick concrete slab underneath. The house is on 2 x12's with 3/4" plywood in the middle resting on 12x 16 filled concrete blocks every 10 ft . The house is 80ft by 20 ft. thanks Jesse

The specs for RC-8 say you can hang up to two layers of 5/8" drywall. The density of is about 600 to 800 kg/m3, so 5/8" drywall weighs about 12kg/m2. Plywood density is anywhere between 400 and 600 kg/m3, so 3/4" plywood would weigh about 11 kg/m3. So very likely you would be fine doing one layer of 3/4" plywood plus one layer of 5/8" drywall, and still be inside the total allowable load. But don't take my word for it: Call Auralex and ask them; they manufacturer it. - Stuart -

thanks for the response I'm only doing one layer of plywood not any drywall. I want the wood ceiling and the acoustics it provides. Also I will have the STC I need with one layer of plywood. Thanks Jesse Matty

I want the wood ceiling and the acoustics it provides.

There's practically no difference in the room acoustics from using drywall or plywood on the ceiling. They have similar mass, similar stiffness, etc., so there isn't much difference in the way the room will sound internally. In any event, for the majority of studios, the inner leaf ceiling should be "hidden" from the room itself, with thick absorption. If not, then the combination of hard ceiling plus hard floor leads to major potential issues with flutter echo and vertical axial modal problems. So there's no reason at all to prefer one material over another for the ceiling, acoustically, since it will not have any effect on the room at all, in the end. Plus, drywall is usually less expensive than plywood, and more dense. There's also the issue of how you would manage to seal between the sheets of plywood: drywall is designed with that in mid, while plywood is not. Airtight seals are critical for isolation.

Also I will have the STC I need with one layer of plywood.

You should never use STC for judging studio isolation! :shock: STC does not take into account the entire low frequency end of the spectrum (or the high end either, for that matter). It was never meant to be used for estimating full-range music isolation. It is meant for the human speech range, as well as typical house, office and school sounds, but not for music. It only covers the rather small band from 125 Hz to 4 kHz. So it completely ignores the bottom two and a half octaves of the human hearing spectrum, as well as the top two and one half octaves. You should never trust an STC rating, when it comes to studios. A wall might be rated at STC 50 but provide terrible isolation for a studio, while another wall rated at only STC-40 would do much better. There is also no relationship between STC and actual decibels of transmission loss: For example, STC-45 does not mean that it will be 45 dB quieter on the other side of the wall. STC numbers have no units: they are just single-number indicators. Also, I thought you lived close to an air-force base, with fighters rattling your roof regularly? A single sheet of plywood won't do much for that. - Stuart -

no I live near an air force base (60+ miles away). The planes do fly over head but not as frequently (military budget cuts) at most twice a week ( have not seen any in a month) and only for less than (5 min and then 5 min back) they are loud but it's easy enough not to record during those times. my walls should be fine at the low end as I gave them a 7" air gap to really help with the low end. one sheet of 1/2" durrock framed wall on 18" centers r-13 fiberglass 6-7" air gap r-13 fiberglass and then 5/8" drywall one sheet. The ceiling will made using the rc8 and plywood (also for looks). I can't float the ceiling due to the fact that one of the would be over 19ft long and according to my calculations I would need to use 2x8's as the joists and I'm not willing to give up 8+ inches of room even with my 9 8" height to play with. I was going to fill the cracks in between the plywood with wood putty or acoustical caulk.