Small Atmos Studio

[Fred Pearson]

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:

Screen Shot 2021-01-28 at 21.32.39.png

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

[gullfo]

this looks to be ok.

[John Steel]

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.

[Fred Pearson]

this looks to be ok.

Great - thanks for the sanity check!

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,

[John Steel]

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.

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/pro ... black.html
Apols if I'm stating the obvious! Looking forward to hearing more. ATB John.

[Fred Pearson]

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.

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/pro ... 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!

[Fred Pearson]

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?

Screen Shot 2021-03-10 at 20.59.49.png

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,

[gullfo]

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.

[Fred Pearson]

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?

[Fred Pearson]

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!):

Baffle Box Sizes.png

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:

Baffle Boxes Plan.png

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,

[gullfo]

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 ) 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.

[Fred Pearson]

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 ) 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.

Screen Shot 2021-06-19 at 21.23.34.png

Thanks,
Fred

[gullfo]

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.

[Fred Pearson]

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?

Baffle Flexible Ducting Gap.jpg

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?

Vent to communal.png

[gullfo]

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.