Studio build in Wales, UK...again!

[Gregwor]

John is the wizard of hangers but I think it looks pretty good other than the tiny little hangers. I'm not sure those are doing any good.

Greg

[Paulus87]

John is the wizard of hangers but I think it looks pretty good other than the tiny little hangers. I'm not sure those are doing any good.

Greg

Hey thanks Greg, how was your vacation? yeah I agree with you - I won't be making hangers that are actually that small, I just did a quick sketch that's not to scale just to demonstrate a concept rather than an accurate design. So if you think the general idea is good then I'll go with that for now.

Things are continuing to progress in the studio, we've started insulating the ceiling bays with the itchy stuff - not a very easy or pleasant job! But it'll be worth it.

Since I'm installing the ceiling corner soffits and will soon construct the rear and front wall framing it's about time I build some silencer boxes, so I come seeking advice to help me make some decisions.

I will have a simple passive inlet and an outlet with a fan, then a mini split for cooling/heating.

I am lucky in that there really is no limit to the size that the silencer boxes can be (within reason) and I could install them either in the cavity between the leaves, or some inside the control room and some in the cavity.

The cavity will be about 13" deep (8" between the framing + 5.5" thickness of the framing) so that would be the limiting factor if I put one or both inside the cavity.

If I put them inside the rooms then they could be even larger since I'll have about 3' of "loft space" in my dual pitched ceiling where the acoustic hangers are hung, plus I'll have space above and behind the middle section of the speaker soffits, and a massive amount of space above the rear wall soffit (around 3' x 7' x 19').

Now here's something that makes this easier; I figured out that I can completely do away with any ducting inside the rooms as I can install the silencer boxes right where I need the in/out vents to be. So the silencer boxes can just have a register on the end and then to join the silencer boxes between leaves I can use either MDF sleeves with a rubber joint, or a little flex duct.

So Greg (or anyone else reading this) you are a total whizz at HVAC now and I'm begging for your expertise. With the above info in mind, could we come up with a design for my silencer boxes together? bearing in mind these boxes are just for air exchange only, so no air con to link in with them. If you are willing to help, please let me know the info you need in order to make the calculations so that we can come up with the dimensions for the boxes plus the amount of baffles within the boxes and I'll draw out some designs.

Here's some info I can give you straight away:
The room volume is approx 5000 cubic feet, let's say they'll be 10 people max in the space at once and then we'll need 6 air changes per hour (I think that's the required amount?) we worked out in some previous posts that I need 154.48cfm, so now how to work out what size boxes I need? please let me know if there's any other info needed to work this out.

Thanks so much,
Paul

[Gregwor]

Hey thanks Greg, how was your vacation?

It was amazing. Crazy to have the cold streak at home with people living in between -45°C and -50°C and then me in Maui living in between 28°C and 30°C! That's literally 80°C difference. Hard to fathom.

I could install them either in the cavity between the leaves, or some inside the control room and some in the cavity.

I can help you for sure but I need you to decide where you want the boxes and then give me the dimensions we have to work in.

The cavity will be about 13" deep (8" between the framing + 5.5" thickness of the framing) so that would be the limiting factor if I put one or both inside the cavity.

This one concerns me because we have to stick to 24"OC which means the silencer can be a max of 22.5" wide and 13" deep (this is if you're willing to only have 1/2" for your MSM gap!). Punching those numbers into my basic silencer box equation:
Y = width = 22.5"
X = (Y-7)/2
X = (22.5-7)/2
X = 7.75"

The length of your box with 3 baffles (I recommend more if you can handle the static pressure) would be:
length = (4X) + 11.5
length = (4*7.75) + 11.5
length = 42.5"

Now, if we did maximize your depth at 13", we will have 2" of MDF + 2" of ductliner eating up that available depth.
So, our inner silencer dimension will be 13" - 2" - 2" = 9"

So, that means our cross sectional area (CSA) within your silencer will be:
CSA = X * inner silencer dimension
CSA = 7.75" * 9"
CSA = 69.75 sq in
CSA = 69.75 sq in / 144 = 0.4844 sq ft

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

CFM (according to what you said was figured out previously) is 154.48cfm

Now, to confirm, is this the CFM if you wanted 6 air changes per hour for the entire space or is this just the amount you need for fresh air?
Note: Entire space CFM would be if we were using forced air and we were exchanging the entire space. Fresh air CFM would be 25-30% of the entire space CFM. This is the amount of fresh air your forced air system would exchange in it's design. If you're using a mini split for heating and cooling, your ventilation design would only have to exchange 25-30% of the air in the room with fresh air. For small spaces (and in the right climate) I will always recommend ductless mini splits for this reason alone. Simply put, the ventilation system (mainly the silencer boxes) take up way less space!

So:
v = 154.48cfm / 0.4844 sq ft
v = 318.93 ft/min

This is just slightly over to the recommended velocity. In a pinch it could work.

Now, we need to ensure that we have the CSA change by at least a factor of two going into the silencer box. So, if our CSA in the box is 69.75 sq in, half of that is 34.88 sq in.

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

Using round duct, that means that the diameter of our inlet duct is:

d = 2 √ (A/π)
d = 2 √ (34.88/π)
d = 6.66"

So you could either use 5" or 6" round duct to feed to your first silencer and then use between the inner and outer silencers. As you said, you can just cut a big square hole in your box with a sleeve to have as your inlet/outlet to your room. If you were concerned with the air velocity you could modify the last little chunk of the silencer box to allow for a larger sleeve penetrating your room.

Sorry if some or all of these calculations are wrong. I just pounded through it quick as my kids were disturbing me.

Use these same steps to figure out the specifications for other potential locations. It all starts off of your available space. If you have unlimited space then of course you're not going to be building your silencers the size of an airplane but I do recommend making them as big as you can within reason. MDF sheets typically come in sheets that are only 4' wide so that's a good starting point for maximum size in both your width and depth. Also, consider how much they are going to cost to build and whether you're going to be able to physically move them into place. If the weight of the silencers is going to be hanging off of your inner leaf joists, make sure your joists can handle the weight as well. It's pretty simple to estimate the weight of the silencers knowing the density of the material you are building them with (MDF for example).

I hope that helped some even though it was just an example for the MSM cavity location.

Greg

[Paulus87]

Hey thanks Greg, how was your vacation?

It was amazing. Crazy to have the cold streak at home with people living in between -45°C and -50°C and then me in Maui living in between 28°C and 30°C! That's literally 80°C difference. Hard to fathom.

I could install them either in the cavity between the leaves, or some inside the control room and some in the cavity.

I can help you for sure but I need you to decide where you want the boxes and then give me the dimensions we have to work in.

The cavity will be about 13" deep (8" between the framing + 5.5" thickness of the framing) so that would be the limiting factor if I put one or both inside the cavity.

This one concerns me because we have to stick to 24"OC which means the silencer can be a max of 22.5" wide and 13" deep (this is if you're willing to only have 1/2" for your MSM gap!). Punching those numbers into my basic silencer box equation:
Y = width = 22.5"
X = (Y-7)/2
X = (22.5-7)/2
X = 7.75"

The length of your box with 3 baffles (I recommend more if you can handle the static pressure) would be:
length = (4X) + 11.5
length = (4*7.75) + 11.5
length = 42.5"

Now, if we did maximize your depth at 13", we will have 2" of MDF + 2" of ductliner eating up that available depth.
So, our inner silencer dimension will be 13" - 2" - 2" = 9"

So, that means our cross sectional area (CSA) within your silencer will be:
CSA = X * inner silencer dimension
CSA = 7.75" * 9"
CSA = 69.75 sq in
CSA = 69.75 sq in / 144 = 0.4844 sq ft

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

CFM (according to what you said was figured out previously) is 154.48cfm

Now, to confirm, is this the CFM if you wanted 6 air changes per hour for the entire space or is this just the amount you need for fresh air?
Note: Entire space CFM would be if we were using forced air and we were exchanging the entire space. Fresh air CFM would be 25-30% of the entire space CFM. This is the amount of fresh air your forced air system would exchange in it's design. If you're using a mini split for heating and cooling, your ventilation design would only have to exchange 25-30% of the air in the room with fresh air. For small spaces (and in the right climate) I will always recommend ductless mini splits for this reason alone. Simply put, the ventilation system (mainly the silencer boxes) take up way less space!

So:
v = 154.48cfm / 0.4844 sq ft
v = 318.93 ft/min

This is just slightly over to the recommended velocity. In a pinch it could work.

Now, we need to ensure that we have the CSA change by at least a factor of two going into the silencer box. So, if our CSA in the box is 69.75 sq in, half of that is 34.88 sq in.

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

Using round duct, that means that the diameter of our inlet duct is:

d = 2 √ (A/π)
d = 2 √ (34.88/π)
d = 6.66"

So you could either use 5" or 6" round duct to feed to your first silencer and then use between the inner and outer silencers. As you said, you can just cut a big square hole in your box with a sleeve to have as your inlet/outlet to your room. If you were concerned with the air velocity you could modify the last little chunk of the silencer box to allow for a larger sleeve penetrating your room.

Sorry if some or all of these calculations are wrong. I just pounded through it quick as my kids were disturbing me.

Use these same steps to figure out the specifications for other potential locations. It all starts off of your available space. If you have unlimited space then of course you're not going to be building your silencers the size of an airplane but I do recommend making them as big as you can within reason. MDF sheets typically come in sheets that are only 4' wide so that's a good starting point for maximum size in both your width and depth. Also, consider how much they are going to cost to build and whether you're going to be able to physically move them into place. If the weight of the silencers is going to be hanging off of your inner leaf joists, make sure your joists can handle the weight as well. It's pretty simple to estimate the weight of the silencers knowing the density of the material you are building them with (MDF for example).

I hope that helped some even though it was just an example for the MSM cavity location.

Greg

Thanks Greg, that's brilliant.

So let's go with the silencers inside the room, I think it makes it a lot easier from both a design and installation standpoint.

What I would like to do is install the inlet box and vent in a large soffit above my rear wall treatment, there is a massive amount of space there to do so. The outlet box and vent could go above the middle section of my front wall, it can either take up some space in the "loft" space or I was thinking it could be a very long but thin (1.5') Y box, of the same volume as the inlet box but with 2 vents on each end where the air will be sucked in by the fan on the other end. Do you think that could work? Then I could have the two vents above my speakers in the soffits. Perhaps the ventilation for the speakers could tie in to this box as well?

To answer your question regarding the total CFM being for replacing the air in the entire room or just the 30% fresh air - in short I don't really know or understand or remember... But here's how the CFM figure was worked out which you said looked good previously:

"If I worked it out using the amount of people then if I said there is going to be 10 people then it would be:

10 x 15cfm = 150cfm

If I worked out using the 30% minium fresh for my room volume with 6 air changes per hour then it would be:

23.92 x 19.57 x 11 x 6 = 30,895.55

30,895.55 / 60 = 514.93

30% of 514.93 = 154.48cfm

So, very similar numbers. I just want to check with you that I have done that all right, and therefore I need to spec a fan/HRV that can provide that amount of cfm?

In the UK we use the metric system and I am only see specs in m3/h, things like this:

Extract Air Performance:
Boost – 100 m3/hour
Trickle – 30 m3/hour

Intake Air Performance:
Boost – 100 m3/hour
Trickle – 30 m3/hour

which means I need to convert my cfm to m3/h:

154.48cfm x 60 = 9268.8

9268.8 = 262.46 m3/h

Have I worked that out correctly?"

In the above calculations my room volume is actually different to what I've ended up with due to me deciding to not beef up my walls internally but to instead clad them using cement board externally, and also the concrete slab taking up a little more space than previously thought. But, I do not know enough about this subject in order to know whether or not I need to replace the entire room volume's air or I only need to replace 30% of it, but I am confident with your help the boxes I build will work and create a safe environment for my space.

Let me know the next step and info you need in order to help you help me!

Paul

[Gregwor]

Paul,

From what you've just shown me, the 154.48cfm looks correct for 30% fresh air. So that's what you should be basing your silencers off of.

Do you think that could work? Then I could have the two vents above my speakers in the soffits.

In theory, yes. You'll have to draw this plan up in SketchUp to see if it will fit in reality (assuming SketchUp's dimensions are accurate to your real life room).

Perhaps the ventilation for the speakers could tie in to this box as well?

Unnecessary. There will be enough air movement in the room to move that air into the return silencer. And really, it's going to be so minimal it's nothing to worry about.

Let me know the next step and info you need in order to help you help me!

I think you've nailed everything on the head with your plan. Go into SketchUp and draw up some silencers with the correct interior cross sectional areas and you're off to the races!

Greg

[Paulus87]

Let me know the next step and info you need in order to help you help me!

I think you've nailed everything on the head with your plan. Go into SketchUp and draw up some silencers with the correct interior cross sectional areas and you're off to the races!

Greg

Ok great, so I assume I can just input some new numbers in to the equations you gave me in your previous reply? If so then I have some questions:

What is the X dimension? The depth? Why do I need to minus 7 before dividing it by the width?

Then why do I need to add 11.5 to the length?

Probably obvious, but I don't understand it yet.

Thanks,
Paul

[Gregwor]

What is the X dimension? The depth? Why do I need to minus 7 before dividing it by the width?

Then why do I need to add 11.5 to the length?

Sorry, I thought I had posted this picture on your thread already:

Gregwor's Silencer Box.png

The equations I used are just based off of this picture. I figured out the simple equations just to speed up the design process. I hope it all makes sense now!

Greg

[Paulus87]

What is the X dimension? The depth? Why do I need to minus 7 before dividing it by the width?

Then why do I need to add 11.5 to the length?

Sorry, I thought I had posted this picture on your thread already:

Gregwor's Silencer Box.png

The equations I used are just based off of this picture. I figured out the simple equations just to speed up the design process. I hope it all makes sense now!

Greg

Hi Greg,

Okay now that I see your diagram that makes a lot more sense, that's brilliant!

So, focusing on just the inlet silencer for now, I've input some figures in to the formulas you gave me and here's what I've come up with:

Width = 24”
X = 8.5”
Length = 45.5”

Outer Depth = 24”
Inner Depth = 20”

CSA = 1.1805 sq. ft

Velocity = 130.859 ft/min

Radius = 85 sq. in
Duct size = 10.4”

Does that sound right?

This would mean my boxes would be roughly L4' x W2' x D2', which means I could utilise the standard 4'x4' MDF sheets very easily.

The boxes will be supported on top of my rear wall treatment framing, which will be more or less free standing, so providing I make it beefy it should easily be able to accommodate such a box on top.

Regarding the duct size of 10.4", this is the size of the hole I need going into the box from the flex duct joining to the corresponding box on the other leaf correct? Is it also the size of the hole which would usually lead to the register? (I will just cut a hole for the air to come out of which will pour out over my mini split)

Now I need to repeat this process for my outlet silencer box which I would like to be a Y configuration; if I keep the volume of the box the same but re-juggle the dimensions so that I can make it fit where I want it, will that work for a Y configuration? There would be two holes leading to the exit hole, which would feed into the corresponding box for the outer leaf, which would be connected to the fan. Would the hole size of 10.4" be the same for all 3 holes?

Paul

[Gregwor]

Radius = 85 sq. in
Duct size = 10.4”

Does that sound right?

Everything up to here makes sense and looks good to me!

For your duct work feeding your boxes (from out size your room of course) can be estimated using this chart:

Feed Duct Size.png

If I worked out using the 30% minium fresh for my room volume with 6 air changes per hour then it would be:

23.92 x 19.57 x 11 x 6 = 30,895.55

30,895.55 / 60 = 514.93

30% of 514.93 = 154.48cfm

Using this info along with the sizing picture above, we can see that a 7" round duct would be great. We can see that the CSA of the 7" round duct is 38.38 sq inches. If the CSA of the silencer box is 170 sq inches, that means we have a CSA ratio of 4.43! That is great!

This would mean my boxes would be roughly L4' x W2' x D2', which means I could utilise the standard 4'x4' MDF sheets very easily.

The boxes will be supported on top of my rear wall treatment framing, which will be more or less free standing, so providing I make it beefy it should easily be able to accommodate such a box on top.

Something to investigate is how much weight you're able to put on the floor itself. These boxes and your framing are not going to be light!

Regarding the duct size of 10.4", this is the size of the hole I need going into the box from the flex duct joining to the corresponding box on the other leaf correct?

You can see above that you could drive the box with a 7" round feed. This can also be the size of duct going between the inner and outer leaf silencer boxes. If you want to use flex duct to join the two that might be hard to find 7" flex duct in your area. If so, you can use a flexible membrane to join the 2 steel ducts (or if your boxes are very close together you could just frame square sleeves (ex: 10"x4" or 8"x6") and use the membrane to join the two. If you can't find 7" anywhere, you could always use 8". You just won't have as great of CSA ratio.

Is it also the size of the hole which would usually lead to the register? (I will just cut a hole for the air to come out of which will pour out over my mini split)

The size of hole that is inside of your room is where your air velocity determines the size. You must keep it under 300 ft per min. It looks like you're at 130.859 ft/min so as long as your hole is the same size as your box CSA you are going to have a very nice slow air velocity!

Now I need to repeat this process for my outlet silencer box which I would like to be a Y configuration; if I keep the volume of the box the same but re-juggle the dimensions so that I can make it fit where I want it, will that work for a Y configuration?

If you don't get the exact CSA that's fine. I recommend just making it as big as you can (within reason of course). Keeping a friendly 4' for material reasons is awesome but not always possible. The Y configuration uses the same principles.

There would be two holes leading to the exit hole, which would feed into the corresponding box for the outer leaf, which would be connected to the fan. Would the hole size of 10.4" be the same for all 3 holes?

Without seeing a rough sketch I'm not understanding what you mean when you say that 2 holes will feed an outer leaf box? If your inner leaf box has to Y, I would make it so that the two holes of the box feed your room, not be used to connect to your outer leaf box. Maybe I'm just not understanding your design here.

Greg

[Paulus87]

Radius = 85 sq. in
Duct size = 10.4”

Does that sound right?

Everything up to here makes sense and looks good to me!

For your duct work feeding your boxes (from out size your room of course) can be estimated using this chart:

Feed Duct Size.png

Greg

Hey that's great Greg, so I will get on and design some boxes now, thanks for all your help so far.

Here's a quick sketch of how I'm thinking to design the inlet box.

I have some questions about the location of the in and out holes for each silencer: Is there a best practice when it comes to positioning these holes? e.g. should they be offset from each other? Is it okay if they are opposite each other (one on each end) with the baffles in between or should one be on the side and one on the front?

Paul

[Gregwor]

Here's a quick sketch of how I'm thinking to design the inlet box.

Tip from experience: design it such that the lid just sits on top to close up the box. Trying to get a nice perfectly rectangular lid to slip into the box is difficult.

Is there a best practice when it comes to positioning these holes? e.g. should they be offset from each other? Is it okay if they are opposite each other (one on each end) with the baffles in between or should one be on the side and one on the front?

I've read that it is recommended to have the inlet and outlet be on a different axis than one another. Like everything in the studio design world, there will be limitations to what you can do so if you have to have it the way you drew this one up, so be it. Just make sure that the inlet and outlet are far enough over that the baffle blocks any sound from blowing through the duct liner and out the hole without having to make the extra few turns.

Greg

[Paulus87]

Here's a quick sketch of how I'm thinking to design the inlet box.

Tip from experience: design it such that the lid just sits on top to close up the box. Trying to get a nice perfectly rectangular lid to slip into the box is difficult.

Is there a best practice when it comes to positioning these holes? e.g. should they be offset from each other? Is it okay if they are opposite each other (one on each end) with the baffles in between or should one be on the side and one on the front?

I've read that it is recommended to have the inlet and outlet be on a different axis than one another. Like everything in the studio design world, there will be limitations to what you can do so if you have to have it the way you drew this one up, so be it. Just make sure that the inlet and outlet are far enough over that the baffle blocks any sound from blowing through the duct liner and out the hole without having to make the extra few turns.

Greg

Thanks Greg. So that is actually how I've designed it, the lid will sit on top, the lip you can see is just so the duct liner on the lid slots in place. I realise now that the baffles should also extend to the top - doh!

I'll try to come up with a way to have the holes on different axis, the box could even be an L shape if needs be I suppose?

Paul

[Gregwor]

I'll try to come up with a way to have the holes on different axis, the box could even be an L shape if needs be I suppose?

For sure! Check out this weird shaped one I designed for my studio:

Note: There are two pictures on this post so you'll have to scroll down to the second picture.

Snail Style Silencer Box Design

Greg

[Paulus87]

Hi guys,

I finally got round to attempting to upload some older pictures from a few months ago to fill in the gaps in my build diary, hopefully this time they'll upload although it seems I have uploaded them in reverse order, so start from the bottom and work your way to the top if you'd like to see them in chronological order. Let me know if you have any questions or spot anything concerning!

Since these pictures quite a lot has been done, I've built some ceiling soffit bass traps, all the walls and ceiling have been insulated as part of the first stage of treatment, and I've finished all the ceiling acoustic hangers, I'll upload the pics asap.

Paul

[Paulus87]

Another picture update, this one is all about ceiling hangers. I still need to upload the pics for the ceiling soffits, windows and insulating, I'll probably get round to that a little later today.