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
How to ventilate an underground garage/basement studio
Originally posted at johnlsayers.com, topic 21621.
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?
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.1) Obviously the first big question is: can this work and allow me to keep my isolation being provided by the inner shell?
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.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?
Both.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.
Typically they live between the two leaves, but they can live outside of your outer leaf and inside of your inner leaf.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.
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.5) What is a supply register and how does it differ to a grille that covers the duct opening
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! GregWould this be a better option?
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. )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.
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.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.5) What is a supply register and how does it differ to a grille that covers the duct opening
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.Would the proposed solution then be acceptable?
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. GregI 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.
. Ok!It should! I'd suggest adding a third baffle into your silencer boxes though
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)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 ;-)
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?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.
You mean like a 90° turn? The baffle is full of turns, so this obviously creates turbulence right?Remember though, if the air sees a drastic change in direction or cross sectional area, turbulence will exist.
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?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.
And it has to be the same thickness as well. It must maintain the surface density of the wall and 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?
Yes. Commonly referred to as the sleeve here on the forum.Is this what is called a flange connector? (see diagram, I think it is from John Sayers designs)
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.What about adding another frame and drywall like in this (see attached diagram)
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: viewtopic.php?f=1&t=20876&p=144060&hilit=garage+door#p144060If this won't do I will "beef up "my garage door as you suggested. Do you have a specific thread in mind?
YesYou mean like a 90° turn?
Yep!The baffle is full of turns, so this obviously creates turbulence right?
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.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?
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.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?
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! GregWhere does one put the inline fan? Can it go in between the two silencer boxes within the machine room?
Ok understood.And it has to be the same thickness as well. It must maintain the surface density of the wall and 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?
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.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.What about adding another frame and drywall like in this (see attached diagram)
Great, thanks!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#p14406If this won't do I will "beef up "my garage door as you suggested. Do you have a specific thread in mind?
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?Yep!The baffle is full of turns, so this obviously creates turbulence right?
Makes sense, good analogy :)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.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?
Ok I will do the measurements you provided earlier and check this outYour 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.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?
Ok but don't I needed 1 X inline fan for supply and another for the return?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!Where does one put the inline fan? Can it go in between the two silencer boxes within the machine room?
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. GregOk but don't I needed 1 X inline fan for supply and another for the return?
Greg, sorry I made a mess of the quotes in the previous post :oops: , 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. cheersCorrect. 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. GregOk but don't I needed 1 X inline fan for supply and another for the return?
You only need one of those fans, not both ;-) To go back on your previous post as per your request: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.
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.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.
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 ;-) GregI 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?
Pics attached
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 :)You only need one of those fans, not both ;-)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.
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?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.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.
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.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 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?
Please don't forget me :(
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.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 :)
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.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?
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.When you say "at some point" do you mean at the outlet or within the actual silencer.
They were designed incorrectly.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.
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.Here is a plan I have of a silencer. it looks even all the way through.
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! GregPlease don't forget me :(
Adding to what Greg said...
When you put a straw in your soda, and suck the air out of the top, then why does soda rise up from the other end of the straw? :) There's your answer... - Stuart -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 makes sense, glad I came onto the forum now as I was going to use 2 fans :oops: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.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 :)
The BIG problem here is that to retain the garage door as an entry point into the studio and, more importantly, into the storage space I can't seal the garage door. This is why I wanted to build the inner and outer leaves and have the silencer penetrate both like this (see image and please note changes). Seeing as this driveway is underground and not noisy 99% of the time, do you think that this could work? I know the insertion loss will be less but I think so long as it helps I will be OK. Not keen on cutting corners but taking a bike or kayak through the studio and up the stairs every time would be too painful :(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.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?
You mean make each baffle a different size within the silencer so if there are 3 you can make the middle one a bit bigger and the 3rd one even bigger?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.When you say "at some point" do you mean at the outlet or within the actual silencer.
do you have a design that I can look at that is designed correctly or could you point me to one/several that will teach me?They were designed incorrectly.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.
What happens if it is?Either way, it looks like your inlet is larger than the path through the baffles.Here is a plan I have of a silencer. it looks even all the way through.
Why does having it the same size cause only one impedance change? I would have thought that you would have no impedance change by keeping the same size throughout.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),
Ok I understand but in this small blue diagram attached (which is what I wanted to do for my room) the outlet is very close to the silencer and indeed very close to the last "corner" within the silencer. So if I have understood you correctly, would this not work?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!
:D Greg[/quote]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!Please don't forget me :(
aaah that does make sense, glad I understood this :)Adding to what Greg said...When you put a straw in your soda, and suck the air out of the top, then why does soda rise up from the other end of the straw? :) There's your answer... - Stuart -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
:thu:aaah that does make sense, glad I understood this :)
Right! It is also possible to use just one fan "blowing" into the fresh air intake end of the duct, and some people do that instead. There are pros and cons for doing it that way. And it is possible to use two fans as well, and miht even be required under certain conditions, but it's a huge pain to implement, because you have to make sure that you get both fans set very carefully to move the exact same amount of air: if not, then one fan will be forcing the other to "over-speed", because it will be moving a little bit more air than it should, so that second fan will wear out sooner than it should, and make more noise than it should. The first fan (the one that is doing the forcing) will also be over-worked, because it is facing a higher load than it should be (forcing the other one to run faster), and therefore it too will wear out faster. If the speed difference is larger, then one of the fans will suffer "aerodynamic stalling" due to air not being able to flow properly over the blades, thus greatly increasing turbulence in the air flow, and noise as well. Thus, for those cases where you do need two fans, it is very important to balance the flows exactly, and monitor them all the time to make sure they stay balanced. Either that, or provide a "relief" path that bypasses the main duct, allowing the excess unbalanced flow to go somewhere else... but that' wastes energy and efficiency.... That's the reason why one single fan is best. - Stuart -That makes sense, glad I came onto the forum now as I was going to use 2 fans
Ok thanks for the recap and that makes total sense. It is incredible just how much intricacy there is to this aspect of studio building. :shock::thu:aaah that does make sense, glad I understood this :)Right! It is also possible to use just one fan "blowing" into the fresh air intake end of the duct, and some people do that instead. There are pros and cons for doing it that way. And it is possible to use two fans as well, and miht even be required under certain conditions, but it's a huge pain to implement, because you have to make sure that you get both fans set very carefully to move the exact same amount of air: if not, then one fan will be forcing the other to "over-speed", because it will be moving a little bit more air than it should, so that second fan will wear out sooner than it should, and make more noise than it should. The first fan (the one that is doing the forcing) will also be over-worked, because it is facing a higher load than it should be (forcing the other one to run faster), and therefore it too will wear out faster. If the speed difference is larger, then one of the fans will suffer "aerodynamic stalling" due to air not being able to flow properly over the blades, thus greatly increasing turbulence in the air flow, and noise as well. Thus, for those cases where you do need two fans, it is very important to balance the flows exactly, and monitor them all the time to make sure they stay balanced. Either that, or provide a "relief" path that bypasses the main duct, allowing the excess unbalanced flow to go somewhere else... but that' wastes energy and efficiency.... That's the reason why one single fan is best. - Stuart -That makes sense, glad I came onto the forum now as I was going to use 2 fans
You totally can. You just need to make sure that the box is isolated from at least one of the leaves entirely. Leave a small gap around the sleeve and fill it with backer rod and caulk. You could maybe over-build the silencer (with more baffles) to try and compensate for the lack of a box on each leaf.This is why I wanted to build the inner and outer leaves and have the silencer penetrate both like this (see image and please note changes). Seeing as this driveway is underground and not noisy 99% of the time, do you think that this could work?
I just recently learned about this trick from Stuart. If he reads this post, maybe he would be willing to elaborate more for us. But as far as I understand it, the more impedance changes there are, the more insertion loss will be achieved. Note, each one will add more static pressure though! And to clarify, you wouldn't make each baffle a difference size, but you would make the path itself larger and smaller. I'm talking the cross sectional area of the air path here.You mean make each baffle a different size within the silencer so if there are 3 you can make the middle one a bit bigger and the 3rd one even bigger?
Not handy, but Stuart posted one a few weeks ago showing his very smart design where he splits the inlet left and right into two paths, utilizing the space in a very smart way! When I have time, I can try and post one of my boxes for you.do you have a design that I can look at that is designed correctly or could you point me to one/several that will teach me?
How well do you breath through your nose if you plug one nostril? Same idea.What happens if it is?
If your box had the same cross sectional area as the inlet, then there would be no impedance change. The example I was referring to implied that the single impedance change occurs when the cross sectional area doubles. From the inlet of 50.27 sq inches to the inside of the box at 100.53 sq inches. Assuming your outlet and register path remains at 100.53 sq inches to maintain a large enough path which would allow an air velocity of less than 300 feet per minute, that only equals ONE cross sectional area change. That means only ONE impedance change.Why does having it the same size cause only one impedance change? I would have thought that you would have no impedance change by keeping the same size throughout.
Your blue diagram has no measurements on it. It's impossible to say whether it would work or not. The only way to tell would be to design the box and look at the numbers to see if it works out. If it doesn't, tweak it until it does. Hopefully that helps! GregOk I understand but in this small blue diagram attached (which is what I wanted to do for my room) the outlet is very close to the silencer and indeed very close to the last "corner" within the silencer. So if I have understood you correctly, would this not work?
Ok thanks for clearing all that up. I feel more prepared to tackle the ventilation now and the only thing really missing is to actually see some silencers in action so if you get a chance, I would really like to see yours or if you or Stuart can think of any other links/info that will help me further, I would really appreciate it.
I might have some more questions closer to build time so will post again in this thread.
I will also make sure to keep you all posted when I actually do start the build and if it helps anyone else down the line, all the better!
Here's one where the top lid is lifted off like a treasure chest for you to examine. You can see the hole on the right of the picture is much smaller than the hole on the left of the picture. The larger hole is obviously on the studio room side of the silencer box and the small hole is on the air handler side. The wood is 2 layers of 1/2" MDF and it is lined with 1" of duct liner. As you can see, is fed with rectangular duct, not round duct. This silencer does not have multiple sizes throughout it and on it's larger hole side, it is hooked up to a longer plenum which would serve to deal with the turbulence issue.
Sweet!! And this longer plenum at the outlet would obviously need to be 3 times the shortest dimension of the silencer right? How big is this silencer? What are my options for lining the interior of the box with?Here's one where the top lid is lifted off like a treasure chest for you to examine. You can see the hole on the right of the picture is much smaller than the hole on the left of the picture. The larger hole is obviously on the studio room side of the silencer box and the small hole is on the air handler side. The wood is 2 layers of 1/2" MDF and it is lined with 1" of duct liner. As you can see, is fed with rectangular duct, not round duct. This silencer does not have multiple sizes throughout it and on it's larger hole side, it is hooked up to a longer plenum which would serve to deal with the turbulence issue.
Ductliner. Only ever use proper ductliner. Do not ever use ordinary insulation products that you would use elsewhere in the studio build. Ordinary insulation will shed fibers and particles over time, poor quality ones will "off-gas" nasty stuff, and all of them will erode due to the air flow. Don't skimp here. Only use the proper stuff, that has been specifically designed for use inside HVAC ducts. You will need the type that is 1" (25mm) thick. It is expensive, yes. Made by several manufacturers. - Stuart -What are my options for lining the interior of the box with?