Rooster studio - new space in existing basement

[missmoo]

Here is the silencer box I've been working on. It's essentially 4' x 2' x 1'. Any feedback, in addition to on my questions in the last post, would be great.

silencer box view with measurements, 6 inch duct, hole.jpg

[missmoo]

Per my question in my recent post, I am wondering about the placement of the vents in the room... whether they would work both on the same wall. I tried to draw some options and would appreciate feedback.

I am just starting to learn Sketchup and I now love it.

If they do work on the same wall, could I get away with them both at the bottom of the room, like this:

bottom placement of ducts.jpg

Or do they need to be staggered, like this:

staggered placement of ducts with air flow arrows and silencers.jpg

[missmoo]

Any thoughts? Bump?

I've been doing research on my own to try to formulate a strategy for the size and placement of the ducts but I'm honestly stuck.

Thanks

[Bigsby]

Hi--
Once again, I'm not the best person to respond, but I think it would be best if you could have your intake at one side of the room and your exhaust at the other, across from it. Do you have room to run a duct across the ceiling in order to accomplish that, and then maybe partially cover that with clouds? Just a thought.....
Mark

P.s. : sorry; I'm not much good with what your duct size should be...

[Soundman2020]

Agree with Bigsby. And I'd also put your return register high up, near the ceiling, where the hot, stale air is.

- Stuart -

[missmoo]

Thanks Guys.

Ok, I should be able to get the register up higher.

I'm curious, though, why it would matter if the registers are on one one versus separate walls. If they are on one wall, they'll actually be about the same distance apart as they would be if they were on separate walls.

If I can "get away" with having them on the same wall, it will be immensely more practical for me right now. As long as I can breath, I'll be reasonably happy. Can I get away with that?

I'd love some feedback on my silencer box design, if possible. I am really having trouble figuring out how to validate my dimensions, as well as determine the necessary duct size. I have the Rod Gervais book and I've been combing through forums, but it's just not clear to me whether I"ve designed the silencer box correctly or if I can get away with a 4 inch duct.

Thanks,
Adam

[Bigsby]

I think the reason it would be better to have them across from each other is that you're trying to exchange the stale air for fresh air. The further apart they are, the more likely that this will work effectively. If they're on the same wall, I'm thinking that the fresh air could just be sucked over to the exhaust, and you wouldn't have a real exchange for your entire room.

Your room is small, so how critical this is, I don't know. I have a fantech fg 6 myself, and it's pretty powerful. Maybe if you set it up to push your fresh air in, and have your exhaust be passive, you could rely on static pressure to vent the room and the power of the fresh air being pushed into the room would be enough to circulate it around the room. The warm, stale air would then naturally rise and find its way out your exhaust vent. I know that Stuart often recommends having a fan at both ends, or in the case of having only one fan, using it at the exhaust end to suck the stale air out, but I put my fan at the intake end, and it works that way, too.

My thought on your silencers is that you shouldn't go any smaller than the way you've designed them. Better to have a larger size duct to move the air--you'd need less velocity and would therefore have less air noise.

However, take all of my advice with a grain of salt--I'm just learning like you are; hopefully Stuart will correct me if I'm leading you astray....

[missmoo]

Thanks Bigsby.

Just curious - how did you determine the measurements for your silencer box? How did you arrive at using a 6" duct? How did you come up with measurements for the path through the silencer box around the baffles? You can see in my design that there is about a 9" x 9" path throughout the box, even around the corners in the box. I have no idea if that is appropriate or whether it will work.

Did you just build it and hope it would work? Or was there some math? Also, I'd love to get away with a 4" duct through the wall, rather than a 6"... but I have no idea how to know if it will suffice. For all I know, smaller is better.

Any thoughts? I'm sure there is some way to calculate this but I have no idea!

Thanks,
Adam

[Bigsby]

Hi Adam--
I must confess I didn't do any math in the design of my silencers. As I'm sure you've seen by now, people here have done all kinds of different approaches/sizes, and I borrowed liberally from the ones that looked good to me. One thing I can say with confidence is that the more turns in your silencer, the better the attenuation. I went with 12" inside my silencer, thinking that the airflow noise would be reduced by the bigger size. However, as you know, I only did a 6" penetration into the room. I don't know the effect this had, whether it negated the fact that I had such a big silencer inside, but I do know that it works very well--it is both quiet and moves the air well. However, I would encourage you not to go down to 4." That just seems too small, and smaller is not better; and I don't remember seeing any threads where people went that small with their fresh air. If I were you. I'd build the silencers and the duct as big as your space allows, within reason. The design that you posted looks good to me, but if you can go bigger than 9" it couldn't hurt. I think going smaller than 9" would hurt, and I think going smaller than 6" for your duct is not a good idea, either. As always, take my advice with water and two grains of salt....

[missmoo]

Thanks Bigsby.

I based my measurements off of your design, seeing that your box on the outside was 2' x 4' x 1'. That's how big my design is, and once you factor the 2 inches of duct liner and multiple layers of OSB it works out to about 9 inches throughout the route. Is that what you did, or did I read your designs wrong?

I'm about to take the plunge because lack of air is preventing me from using my studio. I'll just guess pretty soon. And I'll go with the 6 inch duct through the wall (thanks to your advice).

[Bigsby]

Hi Adam--

Sorry--I misunderstood you--I thought that the 9" dimension was before the duct liner went in. However, I think the outer dimension i had in my plan was before I attached the additional layer of OSB, just so you know. If you're building it based on my design it should work great. I'm glad you're going to go with a 6" duct (that's the inside dimension, right?).

[missmoo]

Thanks again Bigsby. That's reassuring.

And yes, the duct is 6" inside (you can see in my drawing that it's 6" clear, even after the duct lining). It's your exact design with the rabbited out 2x6s and the neoprene.

And now another thing I'm wondering about is the change in velocity for the supply of fresh air. If the silencer box outside the room has the 9" square path, then that joins the 6" duct that passes through the wall, doesn't that duct more than double the velocity of the air rushing into the room? Will that make the system loud there and cause the air to rush into the room? Does the room opening of the fresh air supply duct need to be larger than 6" so there's another decrease in velocity?

[Bigsby]

My guess is that it would be preferable to have a 9" duct to match the inside of the silencer, you'd just have to be sure that you have room in the wall ( avoiding existing framing, wiring, plumbing, etc) to make it that big. When considering the duct liner+ the duct material itself, the outside dimension of the duct would be approaching 14" or so. But if you can make it that big, I think that would be a good idea; I don't think it would hurt you.

[missmoo]

Hmmm.. Stuart, in your post below you said I could make both boxes and ducts the same.

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.

I've been reading some other posts, and in this thread with Bigsby, it sounds like I may have some reason to worry about the 6" duct through the wall causing the air to speed up and "rush" into the room (potentially creating noise?) because the 6" duct has less than half the cross sectional area of 9" square path through the silencer box.

Stuart, do I need to worry about the air speeding up, flowing too fast in the room, and creating noise that way? If so, should I build a 9" duct through the wall instead of a 6" duct?

[Soundman2020]

Stuart, do I need to worry about the air speeding up, flowing too fast in the room, and creating noise that way? If so, should I build a 9" duct through the wall instead of a 6" duct?

It's not so much a problem of "if" the air speeds up, but rather what you do on the other side to slow it down again. For example, if your duct widens out to 9" again right after the wall penetration, and then runs for a couple of feet before getting to the registers, then you are fine: In fact, that sudden double-speed-change can actually be beneficial, to a certain extent, since it is a change in impedance, and that helps to attenuate air-borne sounds somewhat. So as long as you do something after the penetration to slow down the air again, then give it a long straight run after that so the turbulence dissipates, then you should be fine.

- Stuart -