Rooster studio - new space in existing basement

This forum has been so generous with its support during the course of our studio design. The assistance is so appreciated. I am not sure I am doing something wrong,

You are not doing anything wrong at all! Sadly, there's an awful lot of activity on the forum right now, and not too many folks helping out with answers. I wish there were more people answering questions, but right now it is what it is.... :( So it can take a while to get a response.

My question is: how does the double layer of drywall on the inside of the "inside out" wall meet the 2 other outer leaf walls at the corner given that these are not inside out walls?

The drywall on the two does not have to actually meet: As long as the studs in the corner are tightly sealed to each other, and the drywall is firmly attached to the studs, then you are fine. The total surface density of the wood studs is higher than the total surface density of two layers of drywall, so that keeps the mass consistent across the wall.

I am not even sure if I am making any sense....

Perfect sense! I hope I managed to explain the answer as clearly as you explained the question! If not, then I can do a quick diagram for you. - Stuart -

Thank you, again and again. Construction is underway. It is going a lot slower than we have anticipated...for sure.... But, we have completed the installation of the drywall between the joist cavities (the outer leaf). These have been done according to plans. But, the guy who's putting our framing in delivered some materials to the job site this morning for the next round - which includes insulating the existing foundation walls. These foundation walls are to follow Detail 1 and include rigid r-10 insulation on wood furring. Followed by a 1" air gap. Then the 2X4 inner stud wall filled with batt insulation and then get the vapor barrier, the two layers of drywall with green glue. The contractor dropped off foil faced rigid insulation to go against the foundation wall on the furring - and also faced batt insulation? Doesn't that create too many vapor barriers - and put the vapor barriers in the wrong place? Help!

The contractor dropped off foil faced rigid insulation to go against the foundation wall on the furring - and also faced batt insulation? Doesn't that create too many vapor barriers - and put the vapor barriers in the wrong place?

To my way of thinking, yes it does! Brien is the guy who can answer that for sure, but it certainly seems to me that there are going to be multiple potential vapor barriers in there, when you need one, and only one. - Stuart -

I've edited this post to make it more concise. Hopefully this works! ------------ We've got the room built FINALLY. It took 5 months. I cannot thank you enough, Stuart and others in this forum!!!! Now I'm working on incorporating ventilation. From what I've gathered (and please correct me if I'm wrong), I'm going to need two vents: - One vent will pull air from the adjacent basement room into the soundproof room ("fresh air") - One vent will pull air from the soundproof room to another side of an adjacent basement room Here are some questions: 1. Ted White's dead vent designs (here - http://www.soundproofingcompany.com/upload/dead-vent-diagram-profile.jpg call for a minimum footprint of 90" x 24" X 24" (outside of the soundproof space). Are there other designs that are more compact and still effective? What about flatter, smaller baffle boxes? 2. If there aren't other designs that are more compact, I'm afraid that I don't have available space to achieve the 90" x 24" x 24" dimensions. Will the dead vent design still function effectively if I have lower volume? I can easily accommodate 74" x 24" x 24"? I can also accommodate 79" x 24" x 24" for the other vent. 3. If the lower volume designs won't be effective, can I change the dimensions but retain the same volume? I can squeeze in the following dimensions, but would they work? - 74" x 24" x 29" - 79" x 16" x 40" - 79" x 18" x 36" 4. Do I need to build an access panel so I can get to the fan in case something with the fan malfunctions? Or would I just cut open the drywall in that case? 5. How will I "balance" the airflow between the two vents/fans? I know absolutely nothing about HVAC. 6. Can I make up for a smaller footprint by using denser insulation? If I use mineral wool instead of r13 will that help? Thank you!

Any thoughts on the deadvent questions? My progress and music is blocked until I identify the locations for my dead vents and I would greatly appreciate any insights. Thanks

Are there other designs that are more compact and still effective? What about flatter, smaller baffle boxes?

Yes, there are other designs, and yes they can be flatter. The key point is to ensure that the cross sectional area inside the box is larger than the cross sectional area of the duct that feeds it (ideally about twice as much), but apart from that it doesn't really matter how you get to that cross section. It could be square, or it could be a tall thin section, or it could be a short fat section. Here are several examples of what people have done here on the forum: viewtopic.php?f=2&t=1929&start=74 viewtopic.php?t=8425&start=2 viewtopic.php?f=1&t=11542&start=5 viewtopic.php?f=2&t=9761&start=0 viewtopic.php?f=2&t=11485&start=98 viewtopic.php?f=2&t=11508&start=157 viewtopic.php?f=2&t=13821 viewtopic.php?f=1&t=15378&start=44

Do I need to build an access panel so I can get to the fan in case something with the fan malfunctions? Or would I just cut open the drywall in that case?

I would never put the fan inside the silencer box! The silencer is often built into the wall or ceiling cavity, and won't ever be available for access again (unless you want to knock holes in your studio wall! :shock: ). I put the fan outside of the studio, at the far end of the duct, as far away as possible form the room, and in an easily accessible location. The fan also has to be dimensioned correctly for the air flow that you need for your room, based on the calculations that you do.

5. How will I "balance" the airflow between the two vents/fans? I know absolutely nothing about HVAC.

You use variable (adjustable) dampers in-line with the duct, also in accessible locations. The simplest system has only one fan and one damper, even though there are two ducts. So for example, you would have a plain inlet duct with nothing in it (except duct liner, of course) running to the inlet silencer boxes, then the outlet duct (after the outlet silencer boxes) would have the damper in-line, and the fan on the far end. You then open and close the damper to get the correct flow rate. Since the room itself is sealed totally air-tight, the fan sucking air out through the outlet duct will cause fresh air to be sucked in to the room through the inlet duct. In fact, if you have a good variable-speed fan, you might not even need the damper. In more complex systems for multiple rooms, there can be several fans and several dampers, and the dampers can even be electrically controlled by a system controller or thermostat. But you probably don't need something that sophisticated.

6. Can I make up for a smaller footprint by using denser insulation? If I use mineral wool instead of r13 will that help?

The air does not flow through the insulation at any point, and both the silencer boxes and the ducts must be lined with proper duct liner, never with ordinary fiberglass or mineral wool insulation. Duct liner has a special outer layer or coating that prevents air erosion. - Stuart -

I would never put the fan inside the silencer box!

Hmmm. Should I avoid Ted White's dead vent design because it has the fan inside the silencer box (http://www.soundproofingcompany.com/upload/dead-vent-diagram-profile.jpg)? I think he says you can just pop off the front facing pieces of drywall if you ever need to maintain the fan.

The key point is to ensure that the cross sectional area inside the box is larger than the cross sectional area of the duct that feeds it

I'm confused. The duct in Ted White's design is within the silencer box, right? So in that design, the silencer box doesn't feed the duct, right? Also, when you say "cross sectional area", do you mean the surface area? If I want to come up with appropriate dimensions and still use Ted White's concept, should I measure the surface area of the inside of the rectangular silencer box and make sure it's at least twice as large as the surface area of the full length of 6" round flex duct? I've been planning to use this "dead vent" design because my room is already constructed and the walls and ceiling are closed. There aren't any ducts in my walls or ceiling yet, and I was just planning to cut the 6" hole for the PVC pipe supply of fresh air, and another 6" hole for the exhaust. What I like about this dead vent design is that the whole mechanism seems to be outside of my room. If I can stick with this concept it would be great (it seems simple enough), but I'm unsure if I can get away with using different dimensions. How would I calculate the cross sectional area in Ted White's dead vent design? duct: 3.14 (pi) X 3" (radius) ^ 2 = 28.26 How about for the silencer box? I apologize if I'm thinking about this all wrong. I feel like I'm missing something important and probably something obvious. Thanks again

Hmmm. Should I avoid Ted White's dead vent design because it has the fan inside the silencer box

I may be wrong, but I think his entire point with that design is for situations where the fan needs to be silenced, as it has to go inside the structure, and there are no alternatives. I wouldn't suggest that as the design for a silencer box where the fan can be located remotely, outside the studio.

I'm confused. The duct in Ted White's design is within the silencer box, right? So in that design, the silencer box doesn't feed the duct, right?

The way I see it, he is just putting the entire fan inside a box to silence it, while also curving the air path slightly to provide some additional isolation. That's fine, for the purpose it is designed for, but as you can see in the links I posted for you, that's not the way silencer boxes are normally built. Ted's design seems to be specific for the situation where you have no choice but to put the fan inside the studio. You don't seem to have that problem, so you don't need that solution!

Also, when you say "cross sectional area", do you mean the surface area?

The cross sectional area is just taking a cut across the duct itself, and seeing how much "empty space" there is for air to move through. For a round duct, the equation is Pi x r^2. So multiply the radius by the radius, and then by 3.141. So a 6" round duct has a cross sectional area of about 28 square inches (the radius of a 6" circle is 3": 3 x 3 x 3.141 = 28.26). The area of an 8" duct is about 50 square inches. And for rectangular ducts, it is simply the internal height x the internal width. So for a 10" x 12" duct, the cross sectional area is 120 square inches. The general rule of thumb is that the cross section of the air path inside your silencer box should be at least twice as much as the cross section of the duct that supplies it with air. So if you have a 6" duct coming in, then the air path inside the silencer needs to be at least 56". In other words, the open space between the tip of each baffle and the silencer wall needs to measure about 7" x 8" or greater. The reason for this is very simple: if you give the air twice as much cross section to move through, then it must slow down to half the speed. That also creates an "impedance mismatch", which greatly reduces the level of sounds traveling through the duct.

If I want to come up with appropriate dimensions and still use Ted White's concept, should I measure the surface area of the inside of the rectangular silencer box and make sure it's at least twice as large as the surface area of the full length of 6" round flex duct?

You cannot use this concept at all with that design, since the air is not moving through the box! It is inside the duct, and since the duct is always the same size, there is no change in cross section, and no change in air flow speed, and no change in impedance. Ted's design is to stop the FAN NOISE getting into the studio, not to act as a true silencer box for the air-borne noise itself.

I've been planning to use this "dead vent" design because my room is already constructed and the walls and ceiling are closed.

I don't understand why you are so insistent on using that dead vent when it is not applicable to your situation! You need a true silencer box, which can actually be smaller than the "dead vent", if that's what you need, since you can make it flatter than the duct could ever be, provided that you also make it wider. With a true silencer box, you can adjust all the dimensions as needed to get the best fit, without being restricted to the size of the fan motor or the duct. Just use an outdoor fan unit at the far end of the duct, and size the silencer box as small as you need to make it.

There aren't any ducts in my walls or ceiling yet, and I was just planning to cut the 6" hole for the PVC pipe supply of fresh air, and another 6" hole for the exhaust.

PVC pipe??? :shock: That's not the right way to make ducts! Use only proper HVAC duct. Either "flex duct" or normal round sheet metal duct. Don't substitute for products that are not meant to do the job. That is not PVC pipe in Ted's design either: it is flex duct, which is correct.

What I like about this dead vent design is that the whole mechanism seems to be outside of my room.

so it is no different than the normal way of doing a silencer box! In what way do you see it as being different?

If I can stick with this concept it would be great (it seems simple enough), but I'm unsure if I can get away with using different dimensions.

If you insist on following that design, then you are stuck with those dimensions. The limiting factor is the size of the fan motor itself: you cannot make the box any narrower than that, in either dimension (but you could with a normal silencer). And you cannot make the ducts shorter, since you need at least that length to smooth out the turbulence (and resulting high air noise levels) created by the fan itself. The genreal rule is 6 rimes the duct diameter in both directions, so 36 inches up and another 36 inches down (72 inches) plus the fan length (6"?) plus the ducts themselves (8"), plus a few inches clearance top and bottom. Hence, 90". So if you have your heart set on that design, then you have no choice but to follow the dimensions exactly.

How would I calculate the cross sectional area in Ted White's dead vent design?

You don't, because it is fixed. There's no need to calculate anything, since the air never leaves the flex duct, and never enters the box itself. The box is only there to silence the FAN, not the AIRFLOW, since the air never flows through the box, outside of the duct. The box has to be dimensioned at least that big, since tie OD of 6" flex duct is more like 8", plus the radius of the curves: you cannot bend flex duct in a tight corner: it has to be curved gently, hence the need for a box 24" deep, and also wide enough to accommodate the fan (12"?). So with that design, you have no choice but to use the same dimensions that Ted gives. The only way you can use a smaller box, is if you do a normal baffled silencer box, such as the ones I linked you to in my last post, without the fan inside it. Just put the fan at the far end of the exhaust duct, wherever that is, hopefully a long way from the studio. - Stuart -

Ok, so it seems like the dead vent design is overkill based on everything you are saying. That's great because a smaller design will be significantly better for my situation!! I still have some questions and I"m hoping you can validate some of my assumptions. I attached an image of the exhaust system I'm thinking about to pull stale air out of the room. It's crude, but I'm hoping it makes enough sense to get your high level feedback. 1. Since my walls, ceiling, and all drywall is already fully constructed, I would like to put the silencer boxes entirely OUTSIDE of the soundproof space, butting up against the outside of the outer leaf in an unfinished adjacent basement room. This seems to be in contrast to most of the designs you sent links for, most of which seem to have the silencer box integrated into the leaf system (either in between the leaves or somewhat integrated into the inner leaf). Can this type of silencer box work completely outside of the room, outside of the outer leaf? 2. In order to have the silencer box outside of the room, and based on other designs I've seen, I would need to cut a hole directly through the inner AND outer leaf drywall. This would have to be a straight duct that runs from the inside of the room, through the 2 layers of drywall, through the 1 inch airgap, and then through the second 2 layers of drywall (the duct would terminate outside of the room into a silencer box). In running a duct directly through the inner and outer leaf, it seems like I'll be compromising my soundproofing in a significant way (and in a way that I need to deal with). I've tried to capture this duct in blue in the attached image (very rough image, not to scale). 3. In order to mitigate the issue I create by running a duct directly through my inner and outer leaf (the blue duct in my attached sketch), I need that duct to have mass. In Ted White's design, he says that that specific duct penetrating both leaves (I've outlined it in blue on Ted's drawing below) and leading to the silencer box could be thick PVC lined with pipe wrap or MLV. In other designs I've seen, it could be a 6" round duct or a square/rectangular duct lined with duct liner or other HVAC soundproofing material. I am only referring to Ted's design here because it's one example of how to deal with soundproofing the round duct that penetrates directly through both leaves. His use of PVC and pipe wrap is his way of reducing the amount of sound that escapes the duct between the leaves, prior to his "silencer box". I would be happy to use another product, if not PVC, I just haven't seen an example of this in other designs that I understand. It seems like some other people just run a plain metal duct directly through the walls.... which seems like it would prone to have sound go through the thin metal duct and in between the leaves. - What materials and installation technique should I use to run the duct directly through the inner and outer leaf? - How do I avoid the sound escaping the duct between the two leaves and severely compromising the leaf system? - How do I avoid creating a rigid bridge between the two leaves? Should I suspend the duct on neoprene where it goes through the drywall so it's less rigidly connected to the leaves? 4. The duct will go through the leaves and terminate in a silencer/baffle box, which will on it's own have mass and airtightness so it will somewhat function like part of the outer leaf. Like the designs you pointed out to me (thank you!), I'll line that silencer box with duct liner and make it's outer shell massive and airtight. 5. That small silencer box should effectively stop large amounts of sound from escaping the music room, even though the box itself contains very little insulation and their are gaping holes on both ends. The baffles, complex path and impedance mismatch are what will reduce the sound transmission from one side of the box to the other. 6. Since the entire silencer box is outside of the room, I was thinking I could put the fan directly at the end of the silencer box (rather than hooking the end of the silencer box up to another duct with a fan at the end of that). I've included a fan in the sketch that's sitting at the far end opening of the silencer box. - Will it work if I put the fan all the way at the end of the silencer box that is in the unfinished basement area? - Will the fan noise be audible in the room if it's that close to the room itself (even though it's outside of the room)? - If this won't work, how long of a duct should I run to get the fan far enough away so it won't be heard in the space? 7. If this design is actually ok, I was thinking I could essentially create another other of these ducts/boxes for the fresh air supply, but instead just reverse the direction of the fan at the end of the silencer box to push fresh air through the silencer box and into the room. Would that concept work? Thanks! Adam

I hope my post above makes sense. I'm trying my best :D . I just want to :shot:

Hi - I'm sorry to be a nuisance, but does anyone have any advice?

Hi-- I'm sure I'm not the guy you want to hear from (probably you would rather hear from Stuart), and I am far from an expert, but when I read your post it reminded me of my own situation, so I thought I'd chime in. My build is a long, narrow garage with a control room and live room. I have two silencer boxes for each room, one for intake and one for exhaust. If you're curious about the details, you can read my thread here: viewtopic.php?f=2&t=15430 To be brief, 3 out of the 4 silencer boxes I have are in a situation similar to the one you describe. Given my small amount of space, two of my silencers are outside of the outer leaf and one of them is inside the inner leaf. In all three cases, I had to figure out a way to get from the inner leaf, through the air gap, and then through the outer leaf with enough mass to preserve good TL while at the same time avoiding flanking paths from the duct itself. My solution (really Stuart's solution, but my execution) is as follows: 1. I made my "duct" out of wooden 2x material, not metal duct. The reason being that it has mass. I lined it with duct liner. 2. The duct was constructed in two sections, which were rabbited out to accommodate 1/2" of neoprene that wrapped around them, effectively joining them into one duct that avoided creating a flanking path between the leaves. The two sections were roughly 3/16" apart--NOT touching each other. This gap was located between the leaves. 3. Once constructed, I slid the entire duct assembly through holes I cut in both leaves, and then caulked thoroughly. 4. This approach enabled me to maintain the mass that I had built into the walls while avoiding a flanking path that would have occurred if I had built the duct out of one continuous section. The neoprene has enough mass to approximate the mass of the wood duct. For better clarity, you might want to read my thread toward the bottom of the first page and into the second page. This is where I pose my initial question about my problem and Stuart makes his suggestion for a solution. Later on in the second page, you will see some photos of the duct I built which should make the process clear. I am far from finished with my build, but I am able to say that this approach is a very effective solution. With a full rock band playing in the live room, I could only hear them faintly with my ear right up to the silencer opening. So anyway, that's my two cents; I hope it helps.... Mark

Ok, so it seems like the dead vent design is overkill based on everything you are saying.

:thu:

Can this type of silencer box work completely outside of the room, outside of the outer leaf?

Yes it can, depending on how much isolation you need. As Mark mentioned, he did an isolated duct system that bypasses and isolates both leaves, and works great for what he needs. So you can probably do that too. If you need extreme isolation, then you have to have silencers on each penetration of each leaf. Even then, you could do both of those inside the wall cavity, or one in the cavity and one outside the room.

In running a duct directly through the inner and outer leaf, it seems like I'll be compromising my soundproofing in a significant way (and in a way that I need to deal with).

Correct, it is a compromise. In Mark's case, it worked out fine. If you happen to need more isolation than that, you do need a silencer inside the cavity, or inside the room.

that specific duct penetrating both leaves (I've outlined it in blue on Ted's drawing below) and leading to the silencer box could be thick PVC lined with pipe wrap or MLV. In other designs I've seen, it could be a 6" round duct or a square/rectangular duct lined with duct liner or other HVAC soundproofing material.

That's one way of doing it, but the method I outlined for Mark provides even more mass and also better isolation.

It seems like some other people just run a plain metal duct directly through the walls.... which seems like it would prone to have sound go through the thin metal duct and in between the leaves.

Right. Those are the people who either put silencer boxes inside the room, or they have very noisy HVAC systems with poor isolation.... :)

4. The duct will go through the leaves and terminate in a silencer/baffle box, which will on it's own have mass and airtightness so it will somewhat function like part of the outer leaf.

Right again! :) That's why yu need to make it of thick, heavy wood.

5. That small silencer box should effectively stop large amounts of sound from escaping the music room, even though the box itself contains very little insulation and their are gaping holes on both ends. The baffles, complex path and impedance mismatch are what will reduce the sound transmission from one side of the box to the other.

Exactly. As long as the box is built from heavy, thick wood, then it will indeed do its job of silencing quite well.

6. Since the entire silencer box is outside of the room, I was thinking I could put the fan directly at the end of the silencer box

You could do that, yes, but the fan might cause vibrations in the box itself, which would be transmitted into the room. So I would isolate the fan form the box in some way, even it is is only a short piece of flex duct.

7. If this design is actually ok, I was thinking I could essentially create another other of these ducts/boxes for the fresh air supply, but instead just reverse the direction of the fan at the end of the silencer box to push fresh air through the silencer box and into the room. Would that concept work?

Yes it would, but you might be able to skip the fan on this second box: Since the room is sealed air-tight, the first fan (on the outlet) will suck air out of the room, and that reduced pressure will cause the room to "suck" air in from the supply duct. So you might be able to get away with only one fan, if you dimension it correctly. Figure the static pressure imposed by the entire system (both ducts / silencers, and the room itself) then check that against the model of fan you are considering. If the fan can handle that much static pressure and still move enough air volume, then you are OK. - Stuart -

Mark and Stuart - Thank you so much for the information. It's extremely helpful. The neoprene connector makes a ton of sense and it makes me think I should do that for my small PVC cable pass through. A few questions 1. What type of vent cover did you use inside the room? Just curious... 2. Did you use a fan for both silencers boxes (supply and exhaust), per room? Or we're you able to get away with just an exhaust fan, for example? 3. For the silencing to work, I understand that there needs to be change in surface area to create an inpedance mismatch (?). Does the different directions of the airflow in the supply and exhaust boxes mean that the vent openings inside the room need to be different sizes? Do the holes in the silencer boxes need to be different in size depending on the direction of the airflow? Or does it just matter that the sound escaping from the room leaves a smaller duct and that area doubles when it hits the silencer box path? I'm wondering if I can build both boxes, ducts and vents identically... and maybe just skip the fan on the supply box (assuming the single fan is capable of handling that, which I wneed to calculate) Thanks again!

Does the different directions of the airflow in the supply and exhaust boxes mean that the vent openings inside the room need to be different sizes?

Not really. It doesn't matter if the air flow moves from a larger to smaller, or smaller to larger section. It is the change itself that causes the impedance mismatch. Every time the air flow moves from one size duct to another, there is an impedance mismatch. Even at the register itself, where the duct suddenly widens out to the entire room, there is a mismatch. And likewise at the exhaust register, there's another large jump in cross section, from the entire room down to duct size. In other words, you can make everything identical for both the supply and return systems. Some HVAC people suggest that the return duct should be larger than the supply ducts, but for a small project like this, that's not really necessary. Make them all the same. - Stuart -

Great - thanks Stuart. I'm going to work on a design and post the idea here very soon.

Mark was kind enough to send me a detailed design of his own silencer boxes. Extremely helpful. In his design (attached), the hole that leads to the live room is on the 1' (short) side of silencer box. In my situation, I'm wondering if I could shift that hole around to the 2' 1 1/4" side of the box. Doing that would allow me to have the box sit up against the wall outside of my room and it would only protrude 1' out from the wall. If I build it like Mark did, it would protrude 2' 1 1/4" out from the wall. I'd greatly prefer for it to stick out 1' (because I am very cramped for space outside of the room). Is it possible for me to move the hole to where I'm showing it in red below? If you say yes I will be thrilled.

My apologies-- Once I built the boxes, I ended up putting the hole where your red dot is, not where it's shown in the design, for the same reason you want to put it there. Also, I believe the red dot position might actually be preferable, as it effectively creates one more "corner" for the air to travel through. But again, I'm no expert.....

I ended up putting the hole where your red dot is, not where it's shown in the design,

Yup! No problem with that. It does, indeed, add one extra corner. - Stuart -

Excellent. Some more questions, of course. 1. What product should I use for duct liner? Is it special acoustical stuff? Do you know anywhere I can find such a small amount if this material? Could I use aurelex foam panels instead (I have a bunch layer around). 2. Can I use drywall instead of OSB for the silencer box? What are the advantages of OSB? 3. Should I use two layers of drywall/OSB with green glue in between for the silencer? 4. Can the baffles inside be just one layer thick? 5. How thick of OSB should I use (if I don't use drywall). 6. Why am I horrified at the idea of cutting large square holes in my beautiful rock solid new double walls? :D

1. What product should I use for duct liner? Is it special acoustical stuff? Do you know anywhere I can find such a small amount if this material? Could I use aurelex foam panels instead (I have a bunch layer around).

Go to an HVAC supply store--not a box store. They will have duct liner that's designed for that purpose. You should be able to buy just the quantity you need. I believe I used the 1" thickness. My understanding is that the thicker the liner, the better the attenuation.

2. Can I use drywall instead of OSB for the silencer box? What are the advantages of OSB?

I would use OSB--you need the structure. Drywall would not hold together by itself. I suppose you could do plywood as well. I used GG between my layers--seems like a good idea.

4. Can the baffles inside be just one layer thick?

I hope that's ok; that's what I did....

How thick of OSB should I use (if I don't use drywall).

The idea is to match the mass of your leaf, I believe. So if your wall has two layers of 5/8" drywall with GG in between, then ideally you would use material with at least the same amount of mass for your box. I don't think 1/2" OSB has as much mass as 5/8" drywall, but that's what I used. Then again, I haven't read far enough back in your thread to see what your leaf structure is.

6. Why am I horrified at the idea of cutting large square holes in my beautiful rock solid new double walls?

Yeah, I was horrified too! :D But it really is cool to read about these things and then build one and then then see that it actually works! I hope this helps, and I hope Stuart will correct me if I've said anything that's not quite right!! Mark

Hey Mark - That is really helpful. Thanks. Why did you use an 8 inch fan vs a 6 inch? I'm wondering if I could get away with a 6 inch. And, if so, what impact that would have on the whole system, dimensions, etc. Any thoughts? Oh, and I did use 5/8 drywall for my leaves. I have some left over. Maybe I'll use OSB for the first later of the silencer box and 5/8 drywall for the second layer. Did you paint the OSB? I've heard I need to use oil based primer...

Hi-- Actually, the fan is 6"--it's a Fantech FG6, which for my room pushes plenty of air. At the other end, the square hole ended up being 6" as well. I don't see why you couldn't use the drywall as a second layer. I didn't paint mine, but that's probably a good idea; it might reduce the possibility of mold growth. I would think oil-based primer would be the way to go.

and I hope Stuart will correct me if I've said anything that's not quite right!!

Spot on so far! :) :thu:

I used the 1" thickness. My understanding is that the thicker the liner, the better the attenuation.

Yup. 1" is fine, and even though thicker is better, it also takes up a lot more volume. so if you used 2" duct liner, you'd have to male your boxes 2" bigger in all dimensions to still keep the same cross sectional area... So 1" duct liner is good, in most cases.

I would use OSB--you need the structure.

Right!

I hope that's ok; that's what I did...

Yup. Also fine. The baffles are there more to direct the air flow around the corners, than to actually stop the sound (although they do that too!).

The idea is to match the mass of your leaf, I believe.

Right. For maximum isolation, that's what you need.

But it really is cool to read about these things and then build one and then then see that it actually works!

:!: :yahoo: - Stuart -

Ok so I'm working on silencer box designs and trying to figure out how large the duct needs to be that runs through both leaves. I am working from the design of the silencer box suggested earlier in this thread and am trying to properly size the components (size and number of fans and duct) for the room. I am just confused and would appreciate any advice. I can use the Fantech FG6. This pushes 257 CFM. 15 cubic feet of air per minute per person. I hope to fit 4 of us in the room sometimes... The room is 653 cubic feet. So, I need to ventilate 10.84 cubic feet per minute. I think I want to be in the range of 10-12 ACH (right?). So, the fan needs to ventilate 131 CFM. The Fantech FG6 seems ok. I think my next calculation is about the static pressure. I am just getting lost and confused. Is the method for this laid out somewhere? My room is small so I want to figure out if I can decrease the size of the duct that runs between the inner and outer leaf to 4" (cross sectional area is 16) or if I need the 6" (cross sectional area is 36). To illustrate my question about the duct size, I'm wondering if the size inch duct below could be 4 inches (because it would be easier for me to pull off) Then, depending on the size of the duct and whether than impacts static pressure, I'm not sure if that means I'll need a fan for both silencer boxes or I can get awat with only 1 fan or if each silencer box has to have one... And finally, I'm wondering if I can put both the fresh air supply vent and the exhaust vent on the same wall. Because of how I constructed the room, it would be ideal to put both vent/silencer boxes on my long wall that is 10' 9.5". If I put one towards the top left corner of the wall, and the other is towards the bottom right corner of the wall, would that be enough separation between the vents to get proper circulation, even though they are on the same wall? Because my room is so small I'm hoping that would work. I really appreciate all of the help. So, so much. Thanks