How to ventilate an underground garage/basement studio

[buttermuffin]

Hello! I am happy to have found and to be posting on this forum because it seems that is the best resource for this topic and although I have read a lot via the search function I am still unsure about several things when it comes to silencer boxes and ventilation in studio construction in general so I would highly appreciate any help from some of you knowledgeable folks. My space is a 10 X 5m underground garage/basement with brick walls and concrete bricks in the ceiling. I will be using around 7m of the space so my inner shell will be around 7 X 5m. It is located below our house and once the inner shell is built the car entry will be sealed off and I will need to create 2 holes somewhere for supply and return ducts. The diagram gives an overview of the situation and unless someone has a better idea, I intend on having the supply and return ducts as shown ion the interior of the room. There will need to be an inline fan somewhere to provide forced ventilation. So here are my questions so far:

1) Obviously the first big question is: can this work and allow me to keep my isolation being provided by the inner shell?
2) My basement is cool all year round, I have no heat producing gear and I will be the only one down there so is AC necessary?
3) Is a silencer box used for reducing the sound from the exterior coming in through the ductwork or for reducing the sound of air / fan noise coming through the ductwork or both? I ask because obviously, i am worried about losing isolation to the underground driveway by perforating the inner shell.
4)Is a silencer used on the outside of the inner shell or can it be used inside too as I plan to use it.
5) What is a supply register and how does it differ to a grille that covers the duct opening

Thanks you in advance for taking the time to read and help out

[buttermuffin]

If the silencer boxes have to be on the outside of the inner shell, I could consider doing something like this (see diagram attached). Problem is that the storage space we need for our home will be reduced which is not a big deal but it could be in the future if we need to store more stuff. This option would make the south area with the silencer boxes like a machine room which I believe is more inline with how these things are done in the recording studio building world.

Would this be a better option?

[Gregwor]

1) Obviously the first big question is: can this work and allow me to keep my isolation being provided by the inner shell?

To keep things clear for other forum members, your inner "shell" is referred to as your inner leaf. In order to maintain the isolation that your leaves provide, you actually need one silencer box per leaf per penetration. So that means you need 4 silencers boxes.
1 for outer leaf supply. 1 for outer leaf return. 1 for inner leaf supply. 1 for inner leaf return. The "isolation" that silencers provide is actually called insertion loss. It is measured in dB just like isolation is. If your wall provides 40dB of isolation, your silencer must provide 40dB of insertion loss. This is typically achieved by building your silencers out of material that has the same surface density as your walls. A general idea would be that two layers of fire rated 5/8" drywall would be just shy of 5 lbs/sq ft. 1" of MDF is ~5 lbs/sq ft as well.

2) My basement is cool all year round, I have no heat producing gear and I will be the only one down there so is AC necessary?

I'm not an HVAC expert but as far as I know, AC will deal with humidity issues which is an important topic. Temperature-wise, maybe you don't. But you do need fresh air.

3) Is a silencer box used for reducing the sound from the exterior coming in through the ductwork or for reducing the sound of air / fan noise coming through the ductwork or both? I ask because obviously, i am worried about losing isolation to the underground driveway by perforating the inner shell.

Both.

4)Is a silencer used on the outside of the inner shell or can it be used inside too as I plan to use it.

Typically they live between the two leaves, but they can live outside of your outer leaf and inside of your inner leaf.

5) What is a supply register and how does it differ to a grille that covers the duct opening

Register refers to the grill that covers the duct opening. It's important to use one that doesn't produce turbulent noise while allowing air velocity to be slower than 300 ft per min.

Would this be a better option?

This second diagram is closer to being correct. I would suggest providing more detail in your drawing and/or getting on board with SketchUp Make as that's what everyone else on the forum uses and understands. Your diagram shows no doors, no dimensions and lastly doesn't show your silencers having more than one inlet or outlet. Basically, as I wrote in response to your question #1, you need 2 more silencers in that space that would penetrate your inner leaf. The two silencers on the supply would be connected via a flexible connector. The same goes for the return silencers.

Hope that helps!

Greg

[buttermuffin]

To keep things clear for other forum members, your inner "shell" is referred to as your inner leaf. In order to maintain the isolation that your leaves provide, you actually need one silencer box per leaf per penetration. So that means you need 4 silencers boxes.
1 for outer leaf supply. 1 for outer leaf return. 1 for inner leaf supply. 1 for inner leaf return. The "isolation" that silencers provide is actually called insertion loss. It is measured in dB just like isolation is. If your wall provides 40dB of isolation, your silencer must provide 40dB of insertion loss. This is typically achieved by building your silencers out of material that has the same surface density as your walls. A general idea would be that two layers of fire rated 5/8" drywall would be just shy of 5 lbs/sq ft. 1" of MDF is ~5 lbs/sq ft as well.

Hi Gregwor, this is great info thank you. I will be sure to use the same surface density as you suggest and I will refer to the inner shell as "inner leaf" as you say. Would the proposed solution then be acceptable? (please see attached and I apologize for not using sketchup but I was just hoping that for this purpose of explanation a 2D doodle would be easier than trying to explain by words . I also added a door to the machine room from the studio. )

5) What is a supply register and how does it differ to a grille that covers the duct opening

Register refers to the grill that covers the duct opening. It's important to use one that doesn't produce turbulent noise while allowing air velocity to be slower than 300 ft per min.

I thought that the fan (as would be in my case) or the "air handler" (in full HVAC systems) is responsible for the air velocity. Did I get this part wrong? so basically the register at the duct opening on the inside of the inner leaf is responsible for the velocity of the air coming into the room? I did not know this. I thought that it was just a cover for the duct opening.

[Gregwor]

Would the proposed solution then be acceptable?

It should! I'd suggest adding a third baffle into your silencer boxes though. And, then penetration through your leaf should be made out of the same 1" MDF (or equivalent surface density as discussed earlier) material as your silencer box. In your diagram, your sleeve that penetrates the leaf is a tin color, not wood like the rest of the silencer Also, how are you planning on sealing and beefing up the garage door for your machine room? There are some threads on here showing how others have done it.

I thought that the fan (as would be in my case) or the "air handler" (in full HVAC systems) is responsible for the air velocity. Did I get this part wrong? so basically the register at the duct opening on the inside of the inner leaf is responsible for the velocity of the air coming into the room? I did not know this. I thought that it was just a cover for the duct opening.

The fan will move more air, yes. However, the duct size determines how fast that amount of air is moving. Remember though, if the air sees a drastic change in direction or cross sectional area, turbulence will exist. The general rule of thumb is to have your register opening away from any direction or cross sectional area change by an amount of at least 3 times the smallest dimension of the silencer or duct. Smooth transitions (such as the plenum on larger linear slot diffusor registers) will help deal with turbulence.

Greg

[buttermuffin]

It should! I'd suggest adding a third baffle into your silencer boxes though

.

Ok!

And, then penetration through your leaf should be made out of the same 1" MDF (or equivalent surface density as discussed earlier) material as your silencer box. In your diagram, your sleeve that penetrates the leaf is a tin color, not wood like the rest of the silencer

Ah Ok so it is not the duct that penetrates the leaf but a sleeve built as part of the silencer out of the same material? Is this what is called a flange connector? (see diagram, I think it is from John Sayers designs)

Also, how are you planning on sealing and beefing up the garage door for your machine room? There are some threads on here showing how others have done it.

Good point What about adding another frame and drywall like in this (see attached diagram). If this won't do I will "beef up "my garage door as you suggested. Do you have a specific thread in mind?

Remember though, if the air sees a drastic change in direction or cross sectional area, turbulence will exist.

You mean like a 90° turn? The baffle is full of turns, so this obviously creates turbulence right?

The general rule of thumb is to have your register opening away from any direction or cross sectional area change by an amount of at least 3 times the smallest dimension of the silencer or duct. Smooth transitions (such as the plenum on larger linear slot diffusor registers) will help deal with turbulence.

Ok I think I understand so if you have a design where the duct takes a turn it should be allowed to run straight for a certain distance before reaching the register else it may cause turbulence? Do you think the way I have things set up in this design could cause turbulence? I pretty much just have two silencer boxes right next to each other with about half a meter of duct joining them?

Greg[/quote]

Thanks so much Greg, I have one more doubt about this setup. Where does one put the inline fan? Can it go in between the two silencer boxes within the machine room?

[Gregwor]

Ah Ok so it is not the duct that penetrates the leaf but a sleeve built as part of the silencer out of the same material?

And it has to be the same thickness as well. It must maintain the surface density of the wall and silencer.

Is this what is called a flange connector? (see diagram, I think it is from John Sayers designs)

Yes. Commonly referred to as the sleeve here on the forum.

What about adding another frame and drywall like in this (see attached diagram)

No because then your silencer boxes aren't situated between or at the inner and outer leaves. Doors are the maybe the most difficult to build. That extra wall and door is unnecessary material, time, and potential for leakage.

If this won't do I will "beef up "my garage door as you suggested. Do you have a specific thread in mind?

The idea is to seal the heck out of the existing door. Then build a wall in front of it. Put insulation between the door and the face of your wall. The wall can be built just like another studio style wall (thick OSB on door side, then two layers of 5/8" drywall).
Here is a thread discussing it:
http://www.johnlsayers.com/phpBB2/viewt ... or#p144060

You mean like a 90° turn?

Yes

The baffle is full of turns, so this obviously creates turbulence right?

Yep!

Ok I think I understand so if you have a design where the duct takes a turn it should be allowed to run straight for a certain distance before reaching the register else it may cause turbulence?

Having the straight run before the register opening will not prevent turbulence, but it will be upstream further. Think of a river - it has little whirl pools (turbulence). Go a few feet downstream and it is a smooth running river again.

Do you think the way I have things set up in this design could cause turbulence? I pretty much just have two silencer boxes right next to each other with about half a meter of duct joining them?

Your silencers look fine. You could have the silencer inlet oriented differently than the outlet (so inlet would come through the wall horizontally, then the outlet could be out the bottom vertically or out the side). Your current diagram also didn't include a 3rd baffle. You'd have to measure the distance to ensure the turbulence won't be present at your supply outlet. You might have to situate that inner leaf supply closer to the car entry wall to provide a long enough sleeve. And maybe for the others as well.

Where does one put the inline fan? Can it go in between the two silencer boxes within the machine room?

Yes. If you don't want a loud fan outside your place or inside your room, then that's the only place it can go. You can have it on either the supply or the return. Most people put them on the return. Either way, it will work!

Greg

[buttermuffin]

Ah Ok so it is not the duct that penetrates the leaf but a sleeve built as part of the silencer out of the same material?

And it has to be the same thickness as well. It must maintain the surface density of the wall and silencer.

Ok understood.

What about adding another frame and drywall like in this (see attached diagram)

No because then your silencer boxes aren't situated between or at the inner and outer leaves. Doors are the maybe the most difficult to build. That extra wall and door is unnecessary material, time, and potential for leakage.

Oh Ok. Hmmmm but if I seal the garage door off I will lose access via the garage door which I was hoping to retain as an "emergency exit" or even just nice to have a second way to get into the studio. Is there no way around this? What If I was to build the other wall then wouldn't that also make the second silencer void? I guess I am having trouble understanding why having the double wall/door (if built correctly) will compromise the isolation.

If this won't do I will "beef up "my garage door as you suggested. Do you have a specific thread in mind?

The idea is to seal the heck out of the existing door. Then build a wall in front of it. Put insulation between the door and the face of your wall. The wall can be built just like another studio style wall (thick OSB on door side, then two layers of 5/8" drywall).
Here is a thread discussing it:
http://www.johnlsayers.com/phpBB2/viewt ... oor#p14406

Great, thanks!

The baffle is full of turns, so this obviously creates turbulence right?

Yep!

I read somewhere that to get around this is you could make the outlet of the silencer 2 X the size of the inlet. Know anything about this?

Ok I think I understand so if you have a design where the duct takes a turn it should be allowed to run straight for a certain distance before reaching the register else it may cause turbulence?

Having the straight run before the register opening will not prevent turbulence, but it will be upstream further. Think of a river - it has little whirl pools (turbulence). Go a few feet downstream and it is a smooth running river again.

Makes sense, good analogy

Do you think the way I have things set up in this design could cause turbulence? I pretty much just have two silencer boxes right next to each other with about half a meter of duct joining them?

Your silencers look fine. You could have the silencer inlet oriented differently than the outlet (so inlet would come through the wall horizontally, then the outlet could be out the bottom vertically or out the side). Your current diagram also didn't include a 3rd baffle. You'd have to measure the distance to ensure the turbulence won't be present at your supply outlet. You might have to situate that inner leaf supply closer to the car entry wall to provide a long enough sleeve. And maybe for the others as well.

Ok I will do the measurements you provided earlier and check this out

Where does one put the inline fan? Can it go in between the two silencer boxes within the machine room?

Yes. If you don't want a loud fan outside your place or inside your room, then that's the only place it can go. You can have it on either the supply or the return. Most people put them on the return. Either way, it will work!

Ok but don't I needed 1 X inline fan for supply and another for the return?

[Gregwor]

Ok but don't I needed 1 X inline fan for supply and another for the return?

Correct. Just one. One on the return line will pull the air through the supply into the room and push it out the return duct. Remember, when finding a fan that will work, take the static pressure of the entire system into consideration as, like I just said, it's working on both the supply and return line air paths.

Greg

[buttermuffin]

Ok but don't I needed 1 X inline fan for supply and another for the return?

Correct. Just one. One on the return line will pull the air through the supply into the room and push it out the return duct. Remember, when finding a fan that will work, take the static pressure of the entire system into consideration as, like I just said, it's working on both the supply and return line air paths.

Greg

Greg, sorry I made a mess of the quotes in the previous post , please look at it again, you missed a few things.

Regarding what you said here, wouldn't I need to have the fans set up like this? This is what I was going to do, is it wrong? From what I understand about what you said, just one on the return will suck the fresh air from outside through the supply and into the studio while simultaneously getting rid of old stale air.

cheers

[Gregwor]

Regarding what you said here, wouldn't I need to have the fans set up like this? This is what I was going to do, is it wrong? From what I understand about what you said, just one on the return will suck the fresh air from outside through the supply and into the studio while simultaneously getting rid of old stale air.

You only need one of those fans, not both

To go back on your previous post as per your request:

Hmmmm but if I seal the garage door off I will lose access via the garage door which I was hoping to retain as an "emergency exit" or even just nice to have a second way to get into the studio. Is there no way around this? What If I was to build the other wall then wouldn't that also make the second silencer void? I guess I am having trouble understanding why having the double wall/door (if built correctly) will compromise the isolation.

In the diagram where you added an extra wall, you don't have a silencer on your inner leaf. You have 2 on your outer leaves. That is the problem. You can totally build another wall there, but you'd have to situate 2 of your silencers IN your room (eating valuable space. Does your garage door open like barn doors, or doesn't it roll up? You haven't provided any real life pictures for us to see yet. That would be great to see by the way.

I read somewhere that to get around this is you could make the outlet of the silencer 2 X the size of the inlet. Know anything about this?

It isn't a matter of making it exactly 2x the size. Silencers need to double their cross sectional area at some point. Having the silencers change size several times in it make them even more effective. This is creating impedance changes which is what REALLY makes it's insertion loss happen. However, the outlet must be big enough to achieve an air velocity of 300 ft per min or less. This often works out to roughly twice the cross sectional area of the inlet.

I expect some pics of the space

Greg

[buttermuffin]

Pics attached

[buttermuffin]

Regarding what you said here, wouldn't I need to have the fans set up like this? This is what I was going to do, is it wrong? From what I understand about what you said, just one on the return will suck the fresh air from outside through the supply and into the studio while simultaneously getting rid of old stale air.

You only need one of those fans, not both

That is even better but, how exactly does that work? Does the sucking out of old air automatically suck in new air from the other side of the room? Interesting but can't wrap my head around why it would work

Hmmmm but if I seal the garage door off I will lose access via the garage door which I was hoping to retain as an "emergency exit" or even just nice to have a second way to get into the studio. Is there no way around this? What If I was to build the other wall then wouldn't that also make the second silencer void? I guess I am having trouble understanding why having the double wall/door (if built correctly) will compromise the isolation.

In the diagram where you added an extra wall, you don't have a silencer on your inner leaf. You have 2 on your outer leaves. That is the problem. You can totally build another wall there, but you'd have to situate 2 of your silencers IN your room (eating valuable space. Does your garage door open like barn doors, or doesn't it roll up? You haven't provided any real life pictures for us to see yet. That would be great to see by the way.

Good point. I added some pics above The garage door opens upward as you will see and I was hoping to keep our bikes/ kataks there so I have easy access out the house when I go riding or kayaking else have to lag all that stuff up the stairs and through the house. I think I understand what you mean though and I would prefer not to have two silencers inside the actual room. Question: Is it absolutely necessary to have 2 silencers. What happens if I just have a silencer on the outside?

I read somewhere that to get around this is you could make the outlet of the silencer 2 X the size of the inlet. Know anything about this?

It isn't a matter of making it exactly 2x the size. Silencers need to double their cross sectional area at some point. Having the silencers change size several times in it make them even more effective. This is creating impedance changes which is what REALLY makes it's insertion loss happen. However, the outlet must be big enough to achieve an air velocity of 300 ft per min or less. This often works out to roughly twice the cross sectional area of the inlet.

When you say "at some point" do you mean at the outlet or within the actual silencer. Most silencers I have seen built don't have any variation in the size. The baffles are all equal size and the path way within the silencer stays the same. Here is a plan I have of a silencer. it looks even all the way through.
Also, what is the calculation to make sure I am achieving 300cf per minute? My room will be 3500 cubic feet and the 6" fan I am thinking of buying has a capacity of 18000cf per hour.

[buttermuffin]

Please don't forget me

[Gregwor]

That is even better but, how exactly does that work? Does the sucking out of old air automatically suck in new air from the other side of the room? Interesting but can't wrap my head around why it would work

That's exactly how it works. Removing air creates a void that must be filled -- so new air comes in from the path of least resistance.

The garage door opens upward as you will see and I was hoping to keep our bikes/ kataks there so I have easy access out the house when I go riding or kayaking else have to lag all that stuff up the stairs and through the house. I think I understand what you mean though and I would prefer not to have two silencers inside the actual room. Question: Is it absolutely necessary to have 2 silencers. What happens if I just have a silencer on the outside?

I totally understand your desire for storage space.
- You could mount the boxes in the ceiling
- You could mount them in between your inner and outer leaf like you did before, but you would eat up space either in your room or in your storage area.
- You can have 1 silencer, it just doesn't work as well and will only provide mediocre insertion loss. If this is the route you decide to go, let us know so we can tell you how to do it.
- You can have a silencer on the outside, yes.

When you say "at some point" do you mean at the outlet or within the actual silencer.

Having the change occur at the outlet isn't good as there will then be turbulence there. It has to happen within the actual silencer. Usually it happens right at the inlet (when talking about your supply silencer, this would be on the end of the box opposite your room, furthest point from where your room is). Introducing several different impedance changes will increase it's performance. So within your baffles, adjusting the size can achieve this.

Most silencers I have seen built don't have any variation in the size. The baffles are all equal size and the path way within the silencer stays the same.

They were designed incorrectly.

Here is a plan I have of a silencer. it looks even all the way through.

Without seeing it in 3D with dimensions, I can't tell you if it would be good or not. Either way, it looks like your inlet is larger than the path through the baffles. Basically, let's say you have an 8" round inlet duct, your cross sectional area of that inlet is 50.27 sq inches. If you only wanted to introduce a single impedance change (having the size the same throughout), the interior path of the silencer (the inner dimension of the box - this is INSIDE of the 1" duct liner) must be double 50.27 sq inches. So, 100.53 sq inches. Now, based on the CFM required for your room, you also need to calculate how big your silencer needs to be after the last corner in it in order to achieve equal to or slower than 300 feet per min air velocity. This could require you to have your path get larger. Or, maybe 100.53 sq inches will be big enough and you can just retain that size. Now, the outlet itself needs to be away from the last corner (where the last corner or impedance change happens) by at least 3 times the smallest dimension in your box. So, let's say the interior dimensions of your box, in order to achieve 100.53 sq inches is 10", your outlet must be 30" away! You could have a more rectangular path like a 5"x20" at which point your outlet only has to be 15" away. Stuart shared one of his designs in which he splits the path in 2. This allows him to either have a very large cross sectional increase and very slow air speed, OR a smaller cross sectional area per side. This also results in the outlet distance being shorter. Food for thought anyway. Complicated and annoying trying to fit it into your space, always. The bottom line is, I doubt your box fits any of the above requirements/rules.

Please don't forget me

Thanks for the reminder. I saw your last message at a time when I couldn't respond and then I totally forgot to check back into your thread!

Greg