Please help with acoustic baffle box...

[atomicus]

This is somewhat stressing me out, getting my head around the exact specifics of what's required here, as I'm aware how important it is.

I am trying to determine the exact sizing my baffle box should be for air exchange in a small garage conversion. This is NOT hooked up to an HVAC system, it's simply to adhere to the UK regulations for ventilation, which stipulate that there must be four air changes per hour, plus I obviously need to ensure I get air in/out of the room or I'll suffocate lol!

My room is 23 cubic meters. Dimensions are: 2.5m wide, 4m long and 2.3m high. It is stud walls, decoupled from the surrounding brickwork, with a double wall at the end. All walls + ceiling will have double layer pb with green glue. These two end walls are not connected in any way, with a 2-3" gap between them.

I have somewhat of a learning disability when it comes to numbers/mathematics, so some of the equations I've seen are rather complex for me to get my head around.

I do understand the following however...

- The cross section of air flow inside the box should be twice the cross section of the inlet and outlet duct
- I need suitable duct liner for the inside of the box (I have identified this one as being suitable - https://www.advancedacoustics-uk.com/St ... Foam-Panel

Things I am unclear on...

- The exact size my boxes should be
- If I should have one box on the inner-leaf and another one on the outer leaf, i.e 4 boxes, or if 2 will suffice. My main concern is noise leaking out of the room (it will be a home cinema)
- The orientation of the box on the walls, and if this matters?
- I plan on utilising an in-line fan on one or both boxes... my preference is to have one as intake (for positive pressure), but should I have one extracting also?
- What speed should the fan be? I have identified a variable speed one which I think is suitable, but I am not clear how to determine this - https://www.hg-hydroponics.co.uk/phresh ... 6729-p.asp
- I do plan to connect a filter to the fan also, which I'm assuming is OK?

Would very much appreciate any advice. Many thanks.

[Gregwor]

- The exact size my boxes should be

On this thread, I posted a diagram showing how I would design a basic silencer box:

Designing a basic single path silencer box

- If I should have one box on the inner-leaf and another one on the outer leaf, i.e 4 boxes, or if 2 will suffice. My main concern is noise leaking out of the room (it will be a home cinema)

The bigger the silencer box, the larger the impedance mismatch will be and the more insulation will exist in the path which all means more insertion loss. So, if you have one massive silencer box, that would be alright. But, in order to make sure your HVAC won't ruin your isolation, I'd suggest making one per leaf (which means 2 for your supply and 2 for your return) and make them as big as you possibly can.

- The orientation of the box on the walls, and if this matters?

This doesn't matter. Put them where you can fit them while ensuring that your supply and return are at opposite sides of the room.

- I plan on utilising an in-line fan on one or both boxes... my preference is to have one as intake (for positive pressure), but should I have one extracting also?

Only use one fan. A slight improvement can be achieved if you put the fan on the return path.

- What speed should the fan be? I have identified a variable speed one which I think is suitable, but I am not clear how to determine this - https://www.hg-hydroponics.co.uk/phresh ... 6729-p.asp

And

- What speed should the fan be? I have identified a variable speed one which I think is suitable, but I am not clear how to determine this

After designing your HVAC paths (this means designing your silencers boxes and figuring out what type of duct work you will have for the entire system), you can calculate the static pressure of your system. Using that calculation and knowing that you need an air velocity of <300ft/min and your total CFM (if it's just transferring stale air for fresh air) would be ~30% of your entire rooms required CFM (determined using the volume of your room and deciding how many air changes per hour you need -- I recommend at least 6), you can then find an inline duct fact that will move x amount of CFM at x velocity under x amount of static pressure. You can purchase a dimmer/variac type switch for the fan in order to dial in the fan speed.

Here are a couple things to help further:

Flow rate in CFM = ft3/min = [# of air changes per hour X cubic volume of room] / 60 min

Air velocity in ft/min = CFM Flow rate in ( ft3/min) / CSA Cross sectional area in ft2
This is actually expressed as v=q/A

Area of a circle = π r2
Radius = half of the diameter

If you use flat oval duct anywhere:
Area of flat oval =
π (minor radius)2 + [(major diameter- minor diameter) x minor diameter)]
OR
[(π minor 2) / 4] + 3 (major - minor)

BTU = British Thermal Units
This is the quantity of heat required to raise the temperature of one pound of water one degree Fahrenheit

Static pressure is in Pa
Air Handler Unit must be able to handle more Pa than the system is

- I do plan to connect a filter to the fan also, which I'm assuming is OK?

For sure! You SHOULD have a filter. Just do your best to account for the pressure drop caused by the filter in your static pressure calculation.

Greg

[atomicus]

Thank you very much, that's very helpful. I have a few questions though.

- The exact size my boxes should be

On this thread, I posted a diagram showing how I would design a basic silencer box:

Designing a basic single path silencer box

That's great to see, but couple of things... and apologies for what are very basic questions I'm sure...

Why is X given as Y minus 7? Where is the 7 coming from?

I'm still not entirely sure how i work out what Y (and consequently X) needs to be... it seems an arbitrary value which I then add 3 or 2 to?

Sorry, maths makes my brain bleed.

I understand that the diagram shows the box looking down on it from the side... so 'Z' would be how high it is? You say to make Z as big as the calculations say it needs to be to achieve the desired cross sectional area... again I come back to the question of how I know what the cross sectional area needs to be?

The bigger the silencer box, the larger the impedance mismatch will be and the more insulation will exist in the path which all means more insertion loss. So, if you have one massive silencer box, that would be alright. But, in order to make sure your HVAC won't ruin your isolation, I'd suggest making one per leaf (which means 2 for your supply and 2 for your return) and make them as big as you possibly can.

I don't think I have a particularly tight size restriction... as mentioned, I am not incorporating this into an actual HVAC system, it's simply for air exchange, and the boxes will be on the outer leaf of the wall. That said, I don't want MASSIVE boxes protruding into the room, so there is a limit.

Another aspect I am not entirely clear on is what I connect to the holes in the box... would this be metal ducting which then sits inside a hole I obviously have to cut in my wall? I have seen mention of 'sleeves' but I'm not sure what this is exactly? I'm aware that if my box is on the outer leaf, I don't want it bridging or in direct physical contact with the inner leaf at all, yet at the same time a portion of this box will be residing within my inner leaf as air obviously needs to get in/out.

[Gregwor]

Why is X given as Y minus 7? Where is the 7 coming from?

I made the diagram so people don't have to waste time figuring out every detail like where the 7 is coming from

I'm still not entirely sure how i work out what Y

Y is determined by how much room you have in the location where the box would be. For example, say I needed this box to live between some joists that have a 14" space between them. Well, Let's say I want to keep 1" on either side of the box, so that means my box can be 12" wide. That means Y = 12. Now that you know this variable, you can use the formula in the diagram to determine the value of X.

so 'Z' would be how high it is?

Yes. Since my diagram is only 2D, the 3rd dimension could be called Z if you want.

Knowing your necessary cross sectional area within the box (at least double that of the inlet sleeve) and knowing what your maximum X value is, you can easily calculate Z.

Z = desired cross sectional area / X

Remember, Z will be your interior height. So, if you have 1" of duct liner and 1" of MDF, that means 2" extra on the top and 2" extra on the bottom. So, Z + 4" + whatever gap you want to have between the exterior of the box and whatever else is around it.

As you can see, these boxes end up eating up a LOT of space. Especially if you need 4 of them!

again I come back to the question of how I know what the cross sectional area needs to be?

Figure out how much CFM you need (I recommend 6 to 8 air changes per hour)
If this is just for ventilation (dumping stale air outside and bringing fresh air in), you need 25-30% of the total CFM.
Knowing the required CFM, you can use something simple like this chart to determine the duct size you need:

Duct Sizing.png

Once you know your duct size, you can figure out the duct's cross sectional area using the formulas I posted last time.
Double or triple or better yet, quadruple the duct's cross sectional area to determine the cross sectional area inside your silencer box.

At the outlet/register/grille of your duct work, you have to make sure the air velocity is >= 300 ft/min so increase your duct size before the outlet. I believe I included the forumula for that stuff in my last post as well.

and the boxes will be on the outer leaf of the wall.

If you are only going to have outer leaf silencers, you need these to be massive. Basically, make them twice the size as a regular one would be. You also need the sleeve penetrate through both leaves (with a small gap filled with caulk) as to maintain the surface density of your sheathing.

That said, I don't want MASSIVE boxes protruding into the room, so there is a limit.

You won't have any boxes in your room if you only have them on your outer leaf. If you do want great isolation, you will need 4 boxes (2 inner leaf silencers in your room or between your leaves and 2 outer leaf silencers outside of your outer leaf or between your leaves). Depending on the size of your room though, these boxes will be large. And remember, the bigger they are, the better they work.

Another aspect I am not entirely clear on is what I connect to the holes in the box... would this be metal ducting which then sits inside a hole I obviously have to cut in my wall? I have seen mention of 'sleeves' but I'm not sure what this is exactly?

Depending on your design, either you will connect more duct work, or else it would have a grille/diffusor on the sleeve, or heck, you could just leave the sleeve with nothing on it.

The following picture is of a silencer box for an inner leaf that lives between the leaves. So, at one end of the box it's just a round duct inlet that flex duct connected to. The other end of the box has a sleeve on it (just a square made of 1" MDF) that penetrates through the outer leaf sheathing. The sleeve has some duct work on it because it had a fan attached to it. This allows us to penetrate through the sheathing without compromising the surface density of the system.

Big Silencer Done.jpeg

Here is a different box. It is an inner leaf box that has one big sleeve on it (sized for <300 ft/min air velocity).

Nook Ceiling.JPG

In the final picture, you'll see that the builder just put a cheap grille from Home Depot over the end of the sleeve.

Current Nook.jpg

I'm aware that if my box is on the outer leaf, I don't want it bridging or in direct physical contact with the inner leaf at all, yet at the same time a portion of this box will be residing within my inner leaf as air obviously needs to get in/out.

Youll need to leave a 1/4"-1/2" gap around the sleeve and REALLY fill it up with caulk. This will maintain the seal, surface density (as caulk has pretty much twice as much surface density as drywall), and it will decouple the sleeve from the sheathing.

Greg

[atomicus]

If you are only going to have outer leaf silencers, you need these to be massive. Basically, make them twice the size as a regular one would be. You also need the sleeve penetrate through both leaves (with a small gap filled with caulk) as to maintain the surface density of your sheathing.

This small gap with caulk is around the sleeve as it passes through both leafs then? For example, if the box is on the outside of the leaf, I would have this sleeve passing through both leaves, stopping around level with the surface of the inner leaf wall? Do I add the caulk around the gaps in both these areas, as the sleeve passes through outer and inner leaf?

So it seems there is no fixed size they HAVE to be, it's a case of making them as big as you can (correctly sized internally of course), and then utilising the correct fan to meet the CFM requirements?

On the box that has NO fan though, this doesn't change anything, correct? Both boxes should always be the same size?

The following picture is of a silencer box for an inner leaf that lives between the leaves. So, at one end of the box it's just a round duct inlet that flex duct connected to. The other end of the box has a sleeve on it (just a square made of 1" MDF) that penetrates through the outer leaf sheathing. The sleeve has some duct work on it because it had a fan attached to it. This allows us to penetrate through the sheathing without compromising the surface density of the system.

So there would be no need for this kind of metal oval duct work attached to the sleeving on the end the comes into the room... this would typically just end with the sleeve (filled around with caulk as you say) and perhaps a grill of some sort covering it, similar to the last two pictures you posted.

Another thing I was wondering, the position of the in/out on the box... does this matter? It will always be at opposing sides, but does it matter, for example, on the picture of the completed box you posted, if the hole on the right side was on the back? Or is it simply a case of putting it where you need it?

You'll need to leave a 1/4"-1/2" gap around the sleeve and REALLY fill it up with caulk. This will maintain the seal, surface density (as caulk has pretty much twice as much surface density as drywall), and it will decouple the sleeve from the sheathing.

I've seen people use acoustic sealant a lot... would that be the correct product to use for something like this, or are all caulks mostly the same?

Is MDF the best material to use here? I'm sure I've seen some people use thick ply, but MDF is denser so I can see that might be more preferable.

Another thing I've seen some people do is cover finished boxes with a layer (or two) of plasterboard... is there any benefit in doing so, particularly when the box is on the outer leaf? As you have not advocated this, I am guessing not?

This has all been tremendously helpful by the way, thank you very much.

[Gregwor]

This small gap with caulk is around the sleeve as it passes through both leafs then?

Correct.

For example, if the box is on the outside of the leaf, I would have this sleeve passing through both leaves, stopping around level with the surface of the inner leaf wall?

Yes.

Do I add the caulk around the gaps in both these areas, as the sleeve passes through outer and inner leaf?

Yes. You need your outer and your inner leaf to be "air tight" so to speak.

So it seems there is no fixed size they HAVE to be, it's a case of making them as big as you can (correctly sized internally of course), and then utilising the correct fan to meet the CFM requirements?

Correct.

On the box that has NO fan though, this doesn't change anything, correct?

Design-wise, no. So, in the pictures I posted, the one with the duct piece attached to the sleeve is the outer leaf RETURN silencer box. So, the fan attaches to that duct piece and pull air out of the room. This ultimately also pulls are into the room. The inner leaf box is exactly the same other than that is has a bigger sleeve and no duct piece on the sleeve. The bigger sleeve is to achieve slow air velocity (equal to or slower than 300 ft / min)

Both boxes should always be the same size?

Not necessarily. If one is bigger, cool. Again, build them as big as you can fit!

So there would be no need for this kind of metal oval duct work attached to the sleeving on the end the comes into the room... this would typically just end with the sleeve (filled around with caulk as you say) and perhaps a grill of some sort covering it, similar to the last two pictures you posted.

A lot of people just have sleeves sticking into the room like in the example I posted. In my personal design, my inner leaf boxes attach to 12"x12" duct that then feed two linear slot diffusers. This was because I couldn't put the boxes in a place where their sleeves would enter my room at desired locations. It sucks because the duct work and linear slot diffusers are very very expensive.

the position of the in/out on the box... does this matter? Or is it simply a case of putting it where you need it?

Every turn increases the insertion loss which is a good thing. But, every turn also increases static pressure (which can add up fast which means buying a beefier fan which also means higher operating costs). We are all about that insertion loss though, so to answer your question, a good rule of thumb is to have the inlet and outlet at different directions. So, as an example, the inlet would be on the side of the box and the outlet would be on the top. This ALL gets determined when you find locations for your boxes.

Check out one of my personal silencer boxes. There was limited space for this one so I had to get weird with it! (NOTE: this is an older drawing when I was going to achieve my surface density using two layers of 1/2" MDF because that's all I could find for the longest time. Now, I've re-drawn it using 1" MDF)

Weird Silencer.jpg

I've seen people use acoustic sealant a lot... would that be the correct product to use for something like this, or are all caulks mostly the same?

Stay away from the Green Glue Sealant. Their compound is amazing stuff, but sealant should be banned. Seriously.

My personal choice of sealant is DAP brand DYNAFLEX 230 for areas that are not going to be exposed to moisture. It is very cheap and easy to squeeze out and work with. I'm not sure what is available in your area, so if the DYNAFLEX 230 isn't available, I'd recommend buying a small tube of everything that looks promising. It should have labels on it saying things like how long it's guaranteed for and that is is non-shrinking. Something along those lines. For a bit more money I found some true silicone that works very well for sealing but it's SUPER hard to squeeze out. My wrists got wrecked from caulking so much on my build that after seeing specialists and whatnot, I bought a battery powered caulking gun. Anyway, long story short, find a brand/model of caulk that:
- is affordable/cheap
- doesn't shrink
- is easy to work with and clean up
- I personally like the smaller tubes because it's lighter to carry around and it makes it easier to get into tight spaces

Is MDF the best material to use here? I'm sure I've seen some people use thick ply, but MDF is denser so I can see that might be more preferable.

MDF is more dense so you use less space achieving your surface density. Also, in order to get roughly the same surface density as 1" of MDF, you would need two layers of 3/4" OSB. So, that is yet another step of cutting and gluing material together. MDF was just the easiest material to use. The hard part was finding a place that sold 1" thick MDF as all of the big box stores only carried 3/4".

Another thing I've seen some people do is cover finished boxes with a layer (or two) of plasterboard... is there any benefit in doing so, particularly when the box is on the outer leaf? As you have not advocated this, I am guessing not?

Plasterboard is the cheapest material when you're looking for surface density. Sure, you could do something like build the box out of 3/4" OSB and then cover it with heavy 5/8" plasterboard. It's another step though and more caulking, etc. It also doesn't leave much OSB to screw a grille onto or things like that.

This has all been tremendously helpful by the way, thank you very much.

My pleasure. I remember researching, asking and studying HVAC stuff for what felt like endless hours. It's a crazy subject and even my friends that own their own HVAC companies couldn't answer my questions. That's another reason I drew up and posted the basic silencer box design image. That along with any of the other tools I've posted on the forum is save people such as yourself the nightmare of researching it all. I'm just glad to hear that you are actually concerned about and tackling your HVAC!

Greg

[atomicus]

Design-wise, no. So, in the pictures I posted, the one with the duct piece attached to the sleeve is the outer leaf RETURN silencer box. So, the fan attaches to that duct piece and pull air out of the room. This ultimately also pulls are into the room. The inner leaf box is exactly the same other than that is has a bigger sleeve and no duct piece on the sleeve. The bigger sleeve is to achieve slow air velocity (equal to or slower than 300 ft / min)

So this is usually the preference, having the fan extract air from the room? Is there ever a scenario where you'd want the fan bringing air in? Is the intake of air best kept as passive (i.e no fan bringing it in?

Not necessarily. If one is bigger, cool. Again, build them as big as you can fit!

I would imagine though that if I did go with the four boxes, they'd be 'paired' and therefore the same size, as working out the fan speed on two different sized boxes would be a bit tricky? For simplicity, I imagine I'd want to keep them all the same?

On the topic of the four boxes, i.e one on each leaf, how are they linked exactly? I imagine there would have to be some sort of 'break' between the sleeves of the two boxes as they met? Decoupled with caulk or rubber?

[Gregwor]

So this is usually the preference, having the fan extract air from the room? Is there ever a scenario where you'd want the fan bringing air in? Is the intake of air best kept as passive (i.e no fan bringing it in?

You could have the fan on the supply side if you want. Again, the difference is minimal, but from my studies, there is a slight advantage to pulling stale air out of the room.

You should only have 1 fan. Since the room will be a completely sealed system, the fan pulling air out will ultimately pull fresh air in.

I would imagine though that if I did go with the four boxes, they'd be 'paired' and therefore the same size, as working out the fan speed on two different sized boxes would be a bit tricky? For simplicity, I imagine I'd want to keep them all the same?

The HVAC system is seen by the fan as one system. Every cavity and every corner adds up static pressure. Once you figure out the static pressure of the system, that's all the fan cares about. For an easy build, having the boxes all the same size would be ideal. But in real life, it's often hard to find the space for 4 identical box designs.

On the topic of the four boxes, i.e one on each leaf, how are they linked exactly? I imagine there would have to be some sort of 'break' between the sleeves of the two boxes as they met? Decoupled with caulk or rubber?

Any air tight flexible joint will work. The cheapest one would be flex duct. For my personal build, I will be using DuroDyne flexible connectors because the sleeves of my outer and inner boxes are going to be in a very tight spot in some joists.

http://www.durodyne.com/connector.php

Greg

[richroyc]

Any air tight flexible joint will work. The cheapest one would be flex duct. For my personal build, I will be using DuroDyne flexible connectors because the sleeves of my outer and inner boxes are going to be in a very tight spot in some joists.

That's what I used on mine as well - worked out perfectly. The flex connectors come in a strip so I had to sort of hammer them into a square shape but they worked great. The metal on each end makes it easy to attach to the wall frame, probably more sturdy then using flex duct.

IMG_9694.JPG

[atomicus]

You could have the fan on the supply side if you want. Again, the difference is minimal, but from my studies, there is a slight advantage to pulling stale air out of the room.

You should only have 1 fan. Since the room will be a completely sealed system, the fan pulling air out will ultimately pull fresh air in.

Thanks. OK, that makes sense. As I cannot create a vacuum, it figures that air would automatically be pulled in on the side without a fan.

This does bring me on to one of my biggest potential issues however. Due to the layout of the room (which is a former garage), as illustrated on the diagram below, I can only viably have my supply and return air exchange on one wall. There is a bedroom behind the wall at one end, the hallway of the house on the side, and next door's garage on the opposite side.

This only gives me one viable area, the end behind the outer wall second leaf where the garage door resides. Due to planning restrictions, we cannot alter the appearance of the front of the house in any way, so everything must be behind this door. It will still open however, so that affords more airflow as and when necessary, but even as it is, there is a gap all around and it gets very draughty, so it's not as bad as it may sound. It's certainly not a sealed space that I'm putting air into, not by any means. I know this is far from ideal, but it is what it is, and I'm hoping I can find a way to make it work.

It is a somewhat small space (not that the room itself is big), at only 2.75m wide, 80cm deep and 2.7m high.




Consequently, I am wondering if something like the below could possibly work? I have ball-parked the boxes around 60cm W x 30cm D x 90cm H, oriented vertically, so the baffles inside the box would be horizontal, if that makes sense. This feels about right size wise, but let me know if you think I'm way off here.

My plan was to have some built-in units at the back of the room anyway, so I figure I could integrate the baffle boxes into this arrangement, which should work aesthetically.

It is feasible I could have some sort of divider in the middle, if that would help at all, providing this doesn't impede the garage door opening. It couldn't be directly connected to the door, but perhaps something here could keep help with air separation? Obviously I'd also have to ensure the duct for the return and supply were as far from each other as possible.

[Gregwor]

So that I don't have to read through your entire thread again, can you tell me how much of your diagram is already constructed? have you built your walls and such already?

Now, to give some insight to your dilemma, if possible, I would suggest pulling from and pushing air above (providing there are no rooms or anything above).

Other thoughts I have are regarding the positions of your silencer boxes.
1. IF we have to somehow move air to/from the garage door end of your garage, I would suggest putting all 4 silencer boxes in between your inner and outer leaves. That way you aren't eating up space in your room with silencer boxes.
2. How does your garage door open?
3. Could you not put some sort of HVAC covers over holes you cut into your garage door to "hide" the modification?
4. If there is attic space in your garage, could you situate all or half of your silencer boxes up there?
5. If you have any type of gabled roof, you could penetrate on the sheathing part of the building.

Lastly, I appreciate that you're trying to hard to design and build your place correctly. It's awesome and with enough work, you'll have a sweet place!

Greg

[atomicus]

So that I don't have to read through your entire thread again, can you tell me how much of your diagram is already constructed? have you built your walls and such already?

Now, to give some insight to your dilemma, if possible, I would suggest pulling from and pushing air above (providing there are no rooms or anything above).

Other thoughts I have are regarding the positions of your silencer boxes.
1. IF we have to somehow move air to/from the garage door end of your garage, I would suggest putting all 4 silencer boxes in between your inner and outer leaves. That way you aren't eating up space in your room with silencer boxes.
2. How does your garage door open?
3. Could you not put some sort of HVAC covers over holes you cut into your garage door to "hide" the modification?
4. If there is attic space in your garage, could you situate all or half of your silencer boxes up there?
5. If you have any type of gabled roof, you could penetrate on the sheathing part of the building.

Lastly, I appreciate that you're trying to hard to design and build your place correctly. It's awesome and with enough work, you'll have a sweet place!

Greg

The framing of the stud walls is mostly complete, save for the end wall as I still need to get plasterboard and insulation into the room through the garage door... there is no other access for such large items. Once that's in there, the end framing will be completed.

At that stage (and thereafter) the garage door will still open, but only about half way due to the restricted space. The door is a tilt-up/up and over canopy style. Here is an old picture of it (before any work was carried out);



You can see the tracks it runs on, these will be shortened when walls are finished, hence not being able to open fully at that point.

The style of the door would make cutting holes into it rather difficult, certainly hiding them anyway, and I think given how strict the regulations are around here, we wouldn't be able to do it.

There is no attic space in the garage, and the construction of the house is quite unusual, with large concrete slabs/beams between each floor. There is no getting through these, and structurally I don't think that would be advisable, or probably even permissible. Above the garage there is a kitchen... its a slightly odd layout, and 3 floors in total. There is attic space at the very top of the house, but there's no getting to this.

I am not sure how putting all 4 silencer boxes in between the inner and outer leaves would work here exactly? I only have a total of about 30cm here (a 90mm thick inner leaf, air gap of approx 50mm, then 145mm outer leaf. Not sure how I could fit boxes within this, and even if I did, wouldn't this then mean i'd lose all that space for the necessary insulation?

[Gregwor]

Dang.

Okay. Well, the problem with dumping your stale air into and pulling air from that little area where your garage door is is that you're not going to be getting fresh air. You're going to just recycle that stale air and pull it back into your room. You somehow need to get holes cut to the outside of your building to dump the stale air and pull fresh air.

As for the cavity between your leaves for the boxes, I was going to say to just make the gap between your inner and outer leaves bigger to accommodate the size of your silencers. You would then fill the remaining voids in the cavity with insulation. BUT, now that I see what your door looks like, this probably isn't possible because if you move that outer leaf wall closer to the door to make room for the boxes, you won't be able to have any rail length to open the door on. Unless of course you just moved the bottom half of the outer leaf towards the door and stuffed your boxes in there. That would leave the top part of the wall where you initially planned for it to go. Heck, even if you just stuff your inner leaf boxes in the cavity. That way you maximize your space in the studio room.

Greg

[atomicus]

Dang.

Okay. Well, the problem with dumping your stale air into and pulling air from that little area where your garage door is is that you're not going to be getting fresh air. You're going to just recycle that stale air and pull it back into your room. You somehow need to get holes cut to the outside of your building to dump the stale air and pull fresh air.

Yes, I do see your point, it's just that given the restrictions, I can't cut holes in it, and going through the brickwork would be even trickier. I can't imagine there's an 'invisible' way to do this?

I also assume by cutting holes in the door, it would necessitate the boxes being positioned right up close to those vents? That is, the opening of each return and supply, right over a 'hole' of some sort in the garage door? Would it not be enough to have them close to the perimeter bottom edge of the door, where there is an air gap? As I say, this area does get a lot of air flow from outside, but it's still not the same I know.

My other thought was to have some kind of divider, so the air wouldn't 'mix' so easily, but I don't know if that would help at all.

Is there any benefit in switching to pulling air in with the fan, vs extracting it with one? Am I less likely to get a stale air issue that way, or is that just six of one, half a dozen of the other?

[atomicus]

Dang.
Okay. Well, the problem with dumping your stale air into and pulling air from that little area where your garage door is is that you're not going to be getting fresh air. You're going to just recycle that stale air and pull it back into your room. You somehow need to get holes cut to the outside of your building to dump the stale air and pull fresh air.

OK... I MAY have a solution, although I am by no means certain it will work. It could be possible to go through into the hallway for either my return or supply. I've realised there is a space where in which this COULD work, but what do you think?

I've outlined below in another diagram what I think might be possible... basically, looking at the picture of the garage door above, there might be space to go through that wall on the right hand side into the hallway... the box on the outer leaf here could then be dumping air into the hallway.

Alternatively, this could be the intake, but wouldn't it be better to have the fan located within the space behind the garage door, as this will be FRESHER air that could then be brought in to the room? Or should it be the fan on the extract, extracting air into the hallway? The hallway could be intake I suppose also? The air here won't be as fresh though. Quite a few options here as to what's supply and return and where the fan goes... not sure what's optimal?