John Sayers' Recording Studio Design Forum Archive

Well, after two tries at saving a draft, it seems the saving of a draft does not work. Fortunately the second time I tried to save a draft I made a copy.

The room:

Studio is three rooms in basement. Two walls underground (Block wall and spray foam), two walls on interior of basement (double stud wall, staggered) with Roxul Safe and Sound in each wall, putty pads, etc.). Ceiling: 10 inch joists (9 inch actual), with Roxul. All walls and ceilings will be covered with 1/2 and 5/8 drywall with green glue. the two interior rooms (control/mix and isolation) are bordering the underground portion of the basement, and within the envelope of the studio. The interior walls of the control and isolation room are single stud with Roxul and will also be covered with 1/2, 5/8 drywall and green glue, each side.

Also the Studio envelope is about 24 feet long by 13 feet wide. Within the envelope is a 5x5 isolation both and a small 8 x 5 control area. Ceiling is 8 feet high.

Now the questions:
After lots of research and discussion with other about this, there seems to be some contradiction is some areas (or maybe personal preference). For the ceiling, is it best to fill the cavities with the Roxul (9 inches) or leave a gap of air between the top and bottom pieces of Roxul (basically 3 inch Roxul, 3 inch air, 3 inch Roxul)?

Second question. I a looking into the ventilation solution, I do have space outside the room within a suspended ceiling/soffit that can hold the ductwork and mechanicals. Any suggestions of a reasonable solution. I am looking into a duct fan and muffler, but then there is the ducting. Are two fans recommended, on for intake and the other for supply. I will be using air from the rest of the basement to provide air for the studio.

Thank you in advance.

Frank

Hi Frank, and Welcome!

Now the questions:
After lots of research and discussion with other about this, there seems to be some contradiction is some areas (or maybe personal preference). For the ceiling, is it best to fill the cavities with the Roxul (9 inches) or leave a gap of air between the top and bottom pieces of Roxul (basically 3 inch Roxul, 3 inch air, 3 inch Roxul)?

There's no real contradictions here: just math and physics!

It would indeed be better to completely fill the cavity between your leaves. The reason is simple: the insulation acts as a damper on the various types of resonance going on inside your walls. If there is no insulation in there, then resonance rules and the wall does not isolate too well, since the resonances transmit energy between the leaves. To get a better picture of what that means, remove the shock absorbers from your car, but leave the spring in place, then go for a ride on a bumpy road.... then go to the hospital emergency room, to have your internal injuries treated!

Another illustration: Take your socks and shoes off, then jump up and down as hard as you can on solid concrete, and compare that to jumping up and down on a mattress that is resting on the same solid concrete....

So you have the picture: Insulation damps. It removes energy from the system, by converting it to low-grade heat.

It also changes the way the air behaves: It changes over from adiabatic behavior, to isothermal behavior, and it reduces the speed of sound, and lowers the resonant frequency of the system.

One way you can think of it, is that it makes the path seem longer for the sound waves. For every inch of insulation, the sound waves "see" that as being like 1.414 inches of air.

All of those effects combined, add up to A Lot Of Good things!

So does filling the cavity completely work out better than filling it just a bit?

Go back to your "jumping on concrete vs. jumping on a mattress" experiment: Instead of a mattress, start out with just a piece of cloth, such as a sheet. Would that make any difference, as compared to jumping on the concrete? Well, yest it would, but hardly noticeable! Just a very small change. So make it a bit thicker: use a towel, instead of a sheet. Better? Yes, but only slightly. Not much. So how about with a towel and a blanket? Yep, better still, but not great. How about a thin mattress? Getting better, but you still feel the concrete under it. What about with three mattresses and five blankets, and nine towels and seven sheets, all stacked up? Well SURE! Now you don't feel the concrete at all! You are fully isolated from it, by all that damping under you.

The same in your wall: more is better. By filling the cavity entirely, you get the best possible effect. You get the greatest possible extra "distance" (all of the inches times 1.414, not just some of them), the greatest reduction in the speed of sound, the greatest damping, etc.

The difference in isolation between an empty wall and a completely filled wall, can be as much as 16 dB. That's HUGE!

Second question. I a looking into the ventilation solution, I do have space outside the room within a suspended ceiling/soffit that can hold the ductwork and mechanicals

Is that outside your outer-leaf? Or in the cavity between the inner and outer leaf? If it is outside your outer-leaf, that's the best place for it. Don't put it between your leaves, because that means you'd never be able to get to it for cleaning, maintenance, repairs, replacement.... You'd need to tear down your walls or ceiling to do that, if it is in the cavity...

I am looking into a duct fan and muffler, but then there is the ducting. Are two fans recommended, on for intake and the other for supply.

You will need two duct paths: one to supply the fresh air for the studio, and the other to remove the stale air. Each path will need at least one silencer, and perhaps two silencers, depending on how much isolation you need. For high isolation, you need a silencer on the outer leaf, and another on the inner leaf, for each duct. For low isolation, it is possible to get by with just one silencer.

Considering that the room itself is completely sealed, totally air-tight, then blowing air in through one duct will automatically cause air to be pushed out of the other duct. Or sucking air out of one duct would automatically cause air to be sucked in by the other duct. So you only need one fan. It can either "push" air in through the supply duct, or "pull" air out of the exhaust duct. It works ether way.

I will be using air from the rest of the basement to provide air for the studio.

That's probably not legal. You are normally not allowed to use the air from one habitable space as the supply for another habitable space. Check your local building code, to find out it you are allowed to do that.

- Stuart -