Small Atmos Studio

it might be better (for more interior ceiling space, to put the battens on the top of the sheathing that you apply on the rafters. this creates a 50mm air space which can run under the sheathing for the roofing and out the top of the ridge vent. then you'll have the interior rafter space for insulation, lighting, etc. if the exterior sheathing needs to breath fully, then you'll need it perforated to in strips to accommodate (so large temperate differences) and the vapour barrier would be on the inside of the interior ply/drywall. if it doesn't need perforation, then the vapour barrier can be on the top of the rafters before the exterior sheathing. check with you builder on this.

also note: the insulation type - if using the sprayed on closed cell type (SPF) it forms a vapor barrier so you could just add the exterior sheath on the rafters, add mass augmentation if desired, and seal it with the spray on insulation.

Glenn: That's a nice idea as long as a decoupled double leaf assembly is not required. But, even if it is required then your idea can be adapted to accommodate that. Essentially, it's just building another roof on top of the existing roof so that the required air gap can be achieved. Spray foam on the underside of the roof deck and rafters would also do the trick and no longer require any venting, but it is quite an uncommon procedure in the UK. Also, in order for it to work (and not make things a lot worse) whoever sprays it in must ensure that there are no gaps in the insulation at all, the rafters and underside of the roof deck must be completely covered. Paul

Paul, Glenn, Thank you for your help on this and the time you've spent trying to solve my problem - I really appreciate it. Would love to just check my understanding of your proposal Glenn. So top layer would be outer sheathing and roofing - followed by 50mm battens running from eaves to crest. Then where it mentions a vapour barrier - is there, or can there be, a layer of OSB there too, followed by however many layers of plasterboard (picture below). Then I can continue with my MSM system and build a frame within this roof space. Also, my understanding is that out of the two vapour barriers notated, only one is needed dependent on whether the sheathing is perforated or not. What do you mean by perforated - perforated in makeup of the material or perforated as in affixed by punching nails/screws through? Thanks!

perforated in terms of open space for air access but this was based on some drawings i found - so ignore. i think the approach - add the exterior sheathing to the top of the rafters, add mass (or not)_ fill with closed cell spray in insulation, then add drywall layers inside. the insulation will do the necessary vapor barrier. on the outside - if lots of temperature swings - use the batten approach so you have air flow from edge to ridge vent.

Thanks for all your replies, it's given me lots to think about and digest. I'm hoping I've understood the proposals correctly for the ventilation/second roof. I've knocked up an image below: Please save my sanity and tell me that this is all ok haha. I am unsure of the closed cell spray on insulation, what it is exactly and where that should be going. My current plan is to have a vapour barrier (plastic sheeting style) on the outside of my inner leaf. I believe this is the correct place to put it, although please let me know if I've got this completely wrong. Hoping to be able to move on to HVAC and fresh air feeds next. Thanks, Fred

this looks to be ok.

Ola Fred, Great to hear about your project again.

My current plan is to have a vapour barrier (plastic sheeting style) on the outside of my inner leaf. I believe this is the correct place to put it , , .

Yes, in our temperate climate, that would be the place to put it. I think you might also need to install a soffit where the roof over-hangs the walls. Best wishes & keep on keeping on.

gullfo wrote:

this looks to be ok.

Great - thanks for the sanity check!

John Steel wrote:

Ola Fred, Great to hear about your project again.

My current plan is to have a vapour barrier (plastic sheeting style) on the outside of my inner leaf. I believe this is the correct place to put it , , .

Yes, in our temperate climate, that would be the place to put it. I think you might also need to install a soffit where the roof over-hangs the walls. Best wishes & keep on keeping on.

Hey John, thanks for this confirmation. If the outer shell is sealed (i.e. no gap between the top of the walls and the 20 degree roof rafters) can you expand on why soffits might be needed? My knowledge is lacking in this area and any theory/reasoning would really help my end! Cheers,

Hello again Fred, Don't mean to muddy the water here - I noticed that in the drawing, the air gap vents directly to the outside. Conventionally, I think it would be built something like this. The opening is downward facing and you can cover it with a continuous soffit vent to keep out leaves, birds etc - something like this. https://www.roofingsuperstore.co.uk/product/manthorpe-continuous-soffit-vent-10000mm2-244m-black.html Apols if I'm stating the obvious! Looking forward to hearing more. ATB John.

John Steel wrote:

Hello again Fred, Don't mean to muddy the water here - I noticed that in the drawing, the air gap vents directly to the outside. Conventionally, I think it would be built something like this.

Not preserved: Soffit Diag copy.jpg

The opening is downward facing and you can cover it with a continuous soffit vent to keep out leaves, birds etc - something like this. https://www.roofingsuperstore.co.uk/product/manthorpe-continuous-soffit-vent-10000mm2-244m-black.html Apols if I'm stating the obvious! Looking forward to hearing more. ATB John.

Absolutely not stating the obvious at all, thanks for clarifying. Got it, yes you're right, I will need some kind of soffit + vent here to keep out pests - adding it to the list!

I'm moving on to baffle boxes now - already read tonnes on this forum about them but still have some questions. I've worked out what I need size wise and duct wise for the Studio, the Booth and then the volume of both rooms combined. Can I separate it out like in the image below? Combined size for the outer leaf (working out from combined room volumes added together), and then use smaller ducting (7" and 5" for the studio and booth respectively) and appropriately sized baffle boxes for each room? I'm wondering if this will work by splitting up the volumes, or whether it's not as simple as that? Will there be a path of least resistance here that will take all the airflow and leave the other room with none? Is there a better/correct way of doing this? Thanks,

the silencer units need to sit on the mass boundaries to be effective. think in terms of matched pairs. for the big room you'll want 4 big room silencers - 2 for supply, 2 for return. similar for the small room. the silencers are designed to stop sound from entering/escaping via the large holes you're going to create for the ducts - so they need to match the mass of your walls. the contortions in the path ensure no direct sound path to get into/out of of the room. once the duct is in or out of the room, you can route them in that space however you like - e.g. run the duct in an absorptive soffit on the ceiling to position the vents where they work best - no downside since they're only in the room and the hole in the wall is covered. one consideration - the room plenum - using a plenum inside the room allows you to expand the area of the duct which in turns slows down the air velocity which can reduce the any air movement noise. e.g. if your duct is 12"x12" and you create a plenum (doesn't need mass, does need damping to avoid vibration) which is 12"x24" your air velocity will be roughly 1/2. so if your pushing 300fpm in the duct, your air vent velocity will be roughly 150fpm. the return side can benefit as well since your air flow over your vent cover (an air diffuser for example) will be reduced possibly reducing any noise there (although investing in low noise vents is a good idea) in control rooms - symmetry is pretty much everything - so make sure you're balancing the vent system so any noise is symmetrical to the listening position. in live rooms - try to position vents to reduce direct air flow over places where you have a lot of microphones and dynamics - so having a vent blowing on the piano mic or across 7-8 drum mics would be recording any air noise. you might not hear it in the room but the mics can.

Yep, my diagram is not to scale at all and maybe not as clear as I thought. The green squares are the rooms themselves with a baffle box as entry/exit on each end (mass boundary). The larger 'combined baffles' are the baffles on the outer skin allowing air in/out. Do I really need four baffle boxes for each room? I thought one per leaf penetration was enough so 1 outer leaf in, 1 inner leaf in, 1 inner leaf out and 1 outer leaf out. Can I mismatch the ducting between them as shown in the diagram?

Hello, Seeking some clarification on combining baffle boxes. Here are the three sizes I've calculated (will run the figures through the forum once I know this plan is ok to implement, otherwise things will change!): The middle box is the size that I've calculated I need for the Control Room, the right hand box is the size I've calculated I need for the Booth. The left hand box is a sum of the two boxes as I'm hoping to have one baffle box for in/out of the outer leaf that then splits into both the Control Room and Booth boxes. Diagram below to explain: Is this ok to do? Does it take any more complex math than just adding the areas together to create the bigger box? I'm going to struggle to get any more baffles on the outer skin, but if I have to - is it ok to stretch the dimensions so it fits in between the studs, essentially having really long thin baffles as long as the area stays the same? Cheers,

this should be fine, just balance the main system to address each room air flow. also, larger sized plenums inside the rooms (in the ceiling absorption soffits 8) ) can further reduce the velocity and direct the flow. e.g. if you have an 12x12 duct (equiv) into a booth, then adding say a 12x24 plenum which distributes the flow into 2 down vents - you'll decrease the velocity by ~1/2. and using duct board for the plenum it can still act as part of the absorption.

gullfo wrote:

this should be fine, just balance the main system to address each room air flow. also, larger sized plenums inside the rooms (in the ceiling absorption soffits 8) ) can further reduce the velocity and direct the flow. e.g. if you have an 12x12 duct (equiv) into a booth, then adding say a 12x24 plenum which distributes the flow into 2 down vents - you'll decrease the velocity by ~1/2. and using duct board for the plenum it can still act as part of the absorption.

Thanks Glenn, that's super helpful! --- I've since re-thought this plan slightly, and figure that I need to get the combined baffle boxes (the boxes for the outer skin) in between the studs which are spaced only 55cm apart. Working with that 55cm as my 'Y' value in Gregwor's Silencer Box (pasted below) and figuring out 'X' by reversing the formula, I end up with an air velocity of 472.23 feet per minute which is way over the recommended max of 300. How can I get this down to <300? Is it just a case of increasing the 'X' value whilst keeping the 'Y' value the same? If so, I figure I need a 10" (25cm) 'X' with the Y at 21.5" (55cm) - is this a problem? If not, I will get these in the Sketchup and do a long post with all my calculations to make sure I haven't tripped up anywhere. Thanks, Fred

an in-room plenum is used to expand the volume and thereby reduce the speed. so if you had a 12"x12" duct (as an example) if you go into a plenum which is 12"hx18"wx72"wide, and the have two 18"x18" vents on the bottom on each end, you'll reduce you're speed by about half.

Thanks for all the advice so far - really appreciate it! With flexible ducting - does it compress at all? Could I fit a 10" duct through an 8" gap? The compression would be pressed between the two leafs - would this then create flanking? Or can I reduce it to 7" or so through this short section or will that incur a noise penalty for doing so? Trying to figure out the best positioning for the baffles here - it's possible they'll fit in the roof space instead of between the wall studs, making the flexible ducting routing easier (and would mean I can make the baffle boxes the size they should be), but would then have to be vented in the communal area/kitchen rather than venting to outside. Again, is this an issue?

you could use a hard duct as compressing the flex duct would not be good. making a duct from duct board (its like duct liner with a hard exterior which you can cut and tape to make whatever size and shape you need) would give you the interior area for flow and is damped by the nature of its materials. placement - you want symmetry in the control room. so if you place the entry into the room on the side, you should route via the ceiling soffit to ensure you're placing the vents over the listening position in a symmetrical fashion. there should be little or no noise but there will be effects from heat and movement convections.

I'm finding baffle boxes more and more baffling as I delve into them. I'd love to just type down my workings out and see where I'm going wrong as something isn't adding up for me. I recognise that this is going to be a long, arduous post but would really appreciate any advice on this as I've been stuck on baffle boxes for months now and every time I think I get somewhere I come across a new problem. --- Let's start with room dimensions I've added the area and volumes of the studio and the booth together labelled 'both rooms'. This is so I can calculate the size of a single baffle box on the outer skin feeding the air feed in of both the studio and the booth, and also have a box the same size with the air returns, again, being fed by both the studio and the booth. --- Working out baffle box sizes Here are my workings out on how to find out the sizes needed based entirely on Gregwor's silencer box diagram (above) and this post by Gregwor: https://www.johnlsayers.com/phpBB2/view ... gn#p153517 --- Problem So based on those workings out, I need a baffle box to feed both rooms that has a 'Y' value of 27 inches. I've since discovered that I really need to make a baffle box with a 'Y' of 21.5 inches to fit between the studs. I reworked the formula to find the dimensions I need to create a Baffle Box with a 'Y' of 21.5 inches. Ok. So I've found out the size of my baffle and discovered that the 'X' value is 7.25 inches. First issue, is that I need an 8in fan to feed my rooms as outlined in 'Step 2' above. Second issue is that this box ends up being smaller than the baffle for the studio, but bigger than the booth baffle: Clearly this won't provide enough air flow to service both the studio and booth even if I have extended plenums within the rooms themselves. --- Solutions I'm feeling that the solution here is to not combine the baffle boxes on the outer skin for both the studio and booth. This means punching 4 holes in the outer skin rather than 2, and have double the amount of outer skin baffle boxes - but if this is the solution, then that's what needs to be done. --- Questions 1. Are my calculations correct that these are the sizes I need for the rooms? 2. Am I correct that the solution is to create multiple baffle boxes on the outer skin to feed the rooms? 3. Am I ok with the outer skin baffle box feeding the studio being smaller than the one for the inner skin? The studio still requires a 'Y' of 25cms, so having an outer skin baffle with a 'Y' of 21.5 cms again doesn't seem enough. The fan itself needs to be 7in (18cms) to provide enough CFM to the studio so this feels tight. 4. I thought having a 20cm air gap between the studs was going to be loads, but squeezing a baffle box into this tight space seems very difficult (actual air gap is more, as it includes the depth of the studs themselves). How are people doing this with even less space than I have?

so back to basics: 1. room is 1200ft3 and you need a system to provide 6x per hour. so 7200ft3/hr = 120ft2/min = 2ft3/sec. 2. if you have a 1ft2 opening, you need to push through 2ft/sec velocity (120ft/min). these are good velocities. 3. can your system go that low? if not, perhaps some additional duct work and wrap-around cross-duct controls etc. to ensure that. 4. outdoor ventilation - 25%-35% of air needs to be refreshed. so a 50cfm HRV/ERV unit will do it. so... on the silencer question: 1. can you build a silencer that has a 1ft2 profile through out? 2. your in-room plenum - make it so it expands into say 2ft2 profile reducing the speed by roughly 1/2. distribute symmetrically in room. extract symmetrically same way larger plenum into smaller silencer. this should avoid too many calculations and make it simple to build and install. the key is low system velocity.