John Sayers' Recording Studio Design Forum

Hello all you great studio builders. I have some questions about some hvac issues in my new studio.

A bit of background...

The studio consists of two rooms (live and control) and has been built on the first floor of a high rise office building. Walls are dry wall insulated with fiberglass and the frame work lined with a vibration reducing closed cell foam to kill as much flanking as possible and also to seal the walls airtight. Doors are custom made two sides solid wood with fiber glass in between, rebate right around the frame and weather seal (these work really great by the way). The ceiling is a suspended grid in the control room, in the live room the suspended grid cieling is there and a second flush plastered ceiling underneath it, both insulated.

I deliberately didnt use the buildings main hvac system because It would be too "uncontrollable". I installed a large (18 000 BTU) cassette split type aircon unit in the control room ceiling. I did this because it gives the option of easily being switched off whilst recording if it is indeed making too much noise and can be heard over in the live room. I haven't been able to test this yet as it still has to be connected to the compressor outside.

The problem...

The live room is airtight. So much so that you can feel the air pressure jump when you push the door open to enter it. It is also going to get very hot and uncomfortable in there whilst recording i would imagine.

My idea is to put two vents in the live room ceiling, one will have a duct to bring air in from the air conditioned control room and one for air to escape out. Both ducts will have baffle boxes built onto them and as an extra precaution i will build the vents themselves like baffle boxes.

My question is, is this going to create a serious sound bleed between the two rooms? Will the baffle boxes be enough to stop this? Is my idea completely wrong and there is a better solution?

I have included some pictures and a floor plan for you to better visualize. Any help and suggestions are very much appreciated!

Hi SoundBoy, and welcome!

What part of Jo'burg do you live in? I used to live in Hillbrow ( ), but that was waaay back when could still actually survive there for more than 10 minutes. (I mean, over 30 years ago.) It used to be a reasonable place to live back then, but I hear that's no so true today!

Anyway, about your studio:

I'm not quite sure what yo mean by that. Got any photos of how that was done? Closed-cell foam generally doesn't have good acoustic properties, but it all depends on what you did with it: it might be OK. Also, are you talking about the inner-leaf wall being built/sealed like that, or the outer-leaf wall?

How much isolation are you looking for with this construction? It's important to know what your TL goals are, and how much you are already getting, in order to figure out how to handle the HVAC isolation.

Assuming that the "suspended grid ceiling" is not the roof of the building, then that sounds suspiciously like a three-leaf system! Any reason why you didn't take out that ceiling before you put the "second" ceiling in?

You mention a lot about ceilings, but not about walls: How was that LR built? Does it have proper fully decoupled two-leaf MSM walls?

So it sounds like you don't have much isolation in the CR, and the priority is the LR? Any particular reason for that?

Also, when you did the calculations and came up with that 18,000 BTU figure, does that consider the volumes and occupancy of both rooms, or just of the CR? What flow rate and velocity are you using?

Also, if you suspect the the air handler might be audible in the LR, then it must be pretty noisy! What are the specs for it?

I'm thinking it might be better to put another split system in the LR.

Yup! No doubt about that.

Well, that MIGHT work, but it begs the question: Where is the control room getting it's fresh air from, and where is the control room stale air going to?

The way it should be set up right now is that the duct that brings in fresh air to the control room should be tied into the main return duct just before it enters the air handler unit, and the duct that exhausts stale air to the outside should also be tied in to the return duct, but somewhere upstream of the fresh air intake.

So, it might be better to just tap into those ducts (with silencers, of course), rather than pipe air from one room to the other and then outdoors.

In other words, take the duct that is currently bringing fresh, cooled air from the air handler into the CR, just after it exits the air handler, and split that in two with a "T" shaped silencer, one arm of which goes to the CR and the other to the LR. Then do the same with the return duct going back into the air handler: put a "T" shaped silencer in it just upstream of the place where the exhaust duct ties in, and take one arm to each room.

Of course, you'd have to do the math and make sure that your duct sizes and air flow rates/speeds/pressures would still be OK, and you'd have to take care to isolate the ducts at the point they pass through each leaf of your isolation wall, but overall it seems like a better way of doing things than looping through the control room.

At least, that's the way I'd do it. Maybe the HVAC experts here might have a better idea.


- Stuart -

_________________
I want this studio to amaze people. "That'll do" doesn't amaze people.

Hey SoundMan, thanks for the reply

Cool stuff. I live in glen vista and sandton before that. Although I don't think glen vista even existed 30 years ago The studio is actually not far from hillbrow, it's in Marshalltown over on the south west end of the cbd (the nice part of it), in case you know it. Hillbrow is bad these days, I would never live there but it's still not that hectic, I drive through it allot on my way through to Houghton (I have a site there)

Ok to answer your questions. The foam I'm talking about is called SPX33, it's made locally over here by a company called Sondor Performance Foams. Basically we lined the studs and tracks with the stuff on all sides (both board sides, floor and ceiling). The idea was to decouple the walls from ceiling and floor as well as decouple the framework from the boards. I know your probably thinking "pointless" since the screws still couple the boards to the framework but surprisingly enough there was a noticeable decrease in flanking in the walls after we did this. It also creates a completely airtight wall as a bonus.

The walls are all single leaf with the foam padding on the frame work, there are two walls between lr and cr both full of fibre glass and they don't touch each other except for in-between the two glass panes where the gap between the two window frames is closed with a strip of wood. The environment and both rooms are pretty quiet, especially at night and on wkends, which is primarily when I will work.

The suspended ceiling is not the roof. The roof is the next floor above me. A concrete slab about a meter above the suspended ceiling. I am very concerned that this is three leaf now that you said it?! I did this to the LR ceiling basically to create the room within a room.

Lastly, The 18000 btu is big enough to handle both rooms, I was told this by an hvac professional, the unit itself is a second hand one I had lying in storage that I pulled out of an old board room, I had it checked to see if it would run but I've never run the unit since it's not connected yet, although I think it's time I tried to find some info on its specs, thanks for bringing it up. Worst case scenario if it is too loud I will have to put two new split units in I guess. So your basically suggesting I use the buildings existing HVAC system? I really don't think it will work as the system is not very well understood by the building managers and I really don't trust it. Its also very noisy as the vents I have access to really blast out the air. I can look into it and see if we can tie into it somehow, maybe use bigger ducts to slow down the air and baffles but I would much rather put our own fresh air ducts in and out if it's possible and then condition. Sorry again for the very long post! Lots to explain

I have tried to attach pictures but every time i upload a picture to the post it just logs me out and says I must log in. I have tried deleting board cookies as well as tried on chrome and explorer. Not sure why the board is doing it? Will keep trying to post pics as replies.

Edit: After further testing, I am not happy with isolation of the Live room. Have made a post about it.

Here you can see The foam (black) on the frame work of the walls.

We built the walls right up through the suspended ceiling to the concrete slab above