Basement studio/drum room advice needed

[ScotcH]

Here is the latest revision. I think this is basically the final layout and design. The HVAC meets the needs for air supply, and the noise should be fairly well contained, or at least as best as can be given the goals and what I'm willing to compromise on.

HVAC overall layout

Return baffle boxes

Overhead layout view

West cross-section

[Starlight]

Source of the postbasement top 3d-2.jpg

Sorry, ScotcH, but it looks to me in the above and some other images that you have two baffles in series on both the in and out airflows, but not as I would expect, which would be one pair on the outside of the outer room and the other pair on the inside of the inner room, each silencer box being attached exactly where the air enters or exits each wall of the two-walled studio.

Is there sometrhing I am not seeing correctly? Or is there something you have not fully understood about silencer placement?

[ScotcH]

I think I understand, but let's walk through it:
- Baffles are needed on both sides (ie, on the inner and outer leaf)
- inner baffle and outer baffle must be decoupled from each other
- the boxes mass should match the leaf mass
- flow should slow down at the exit into the room

Now I don't recall reading that the baffles must be exactly at where the air enters or exists ... maybe I missed this? I was under the impression that the baffles must be decoupled from each other, and each box is coupled only to the given leaf (inner or outer).

In the above layout, the boxes are in serial layout due to space considerations ... but they are coupled to separate leaves. The left box is the supply to the room, and is decoupled from the joists. A duct passes through the inner leaf. The right box is attached to the joists (outer leaf), and is not coupled to the inner leaf, or the other box (pipe in the middle is sealed with insulation/caulking, not hard attached).

For the return boxes, same idea. The left box is coupled to the inner leaf framing, then the pipe and outer box is decoupled from that and sitting outside the room.

Here is a closer detail with framing. This is the inner leaf box, penetrating the ceiling drywall. It sits in the joist space, but it is not coupled to the joist (the outer layer of insulation is the decoupler).

This is the outer leaf box. Also in the joist space, but its actually attached to it, so the outer leaf. The joining pipe form the inner leaf box is decoupled from this box, again with insulation at the joint:

Does that make more sense, or am I still out to lunch?

Thanks for reviewing and chiming in!

[Starlight]

Source of the postDoes that make more sense, or am I still out to lunch?

I have to admit that I still don't see it, but that is my problem, not yours, so long as you are confident with what you are doing. I am definitely not suggesting you are out to lunch!

I am expecting to see the two walls (technically, leaves, as they may be the ceiling) through which the ducts travel, showing me one silencer on the outside and the other on the inside, for both the incoming and the outgoing air. I have drawn two imaginary red walls to show what I am looking for.

Source of the postI think I understand, but let's walk through it:
- Baffles are needed on both sides (ie, on the inner and outer leaf)

Yes, the best isolation is to be had by having 4 baffle boxes as you describe.

Source of the post- inner baffle and outer baffle must be decoupled from each other

Yes, because the rooms are decoupled the duct connecting the baffle boxes must also be decoupled. If you don't you create a flanking path and negate the work you have done to decouple the rooms.

Source of the post- the boxes mass should match the leaf mass

That would be ideal but is not always the case.

Source of the post- flow should slow down at the exit into the room

Again, that would be ideal but is not always the case.

Source of the postNow I don't recall reading that the baffles must be exactly at where the air enters or exists ...

If you have a wall and a baffle box with the same (or almost the same) mass, what happens if the duct between the wall and the baffle box doesn not have the same mass? It would be a point where sound can get into the duct and enter or excape the room, bypassing the baffle box. Can you see why it is necessary to have baffle boxes butted right up against the hole in the wall?

Source of the post... (pipe in the middle is sealed with insulation/caulking, not hard attached)... (the outer layer of insulation is the decoupler) ...The joining pipe form the inner leaf box is decoupled from this box, again with insulation at the joint: ...

Is your duct hard (solid) or soft (eg. flexiduct)? If it is flexiduct then it will sufficiently dampen flanking noise that it can be considered decoupled even though it will run continuously from one wall to the other. If the duct is solid there needs to be a break at some point. I used a short length of flexiduct between the walls, I have seen homemade cloth tubes and can imagine that there are other ways of bridging a break in a solid duct in a way that does not couple the ducts nor the walls while maintaining a smooth airflow.

You mention separately that you are using caulk and insulation to decouple your duct. Caulk will dampen but I do not know whether that it sufficiently soft to provide decoupling. Insulation has next to no mass so it would not be a good idea to use that as it will act as a hole and let sound through.

I see these as alarm bells, warning me of potential (unfortunate) mistakes but, as I started off by saying, that is my problem, not yours, so long as you are confident with what you are doing.

[ScotcH]

Ok, good points about the caulk not acting as decouple. So, let's replace the joining duct with a flex duct. That makes sense.

Let's look at these 2 diagrams. Here is the typical 2 leaf wall/ceiling, with baffle box on each leaf, and a flex duct joining them:

Can we agree that this is a proper (simplified) decoupled silencer box design?

Now here is what I am trying to achieve:

The reason to move the boxes in between the leaves is for space ... I cannot put them outside the leaves. So the only other alternative is to no have any boxes at all (unless I'm not seeing another possibility).

You mention the mass of the duct itself, and the need to have the baffle right against the hole itself. Thanks for confirming that, and of course it makes sense. However, my issue is that since the main HVAC duct is literally right next to the outer leaf, there is not space at all for a baffle box on the OUTSIDE of the outer leaf. So, the alternative is to put it on the inside of the outer leaf. Now, having said that, and based on your input, this might actually be pointless, as there is a duct running from the main HVAC trunk, through the outer leaf, and to this box (a good 10 feet or so).

I would need this baffle somehow right at the point that it penetrates the outer leaf. I don't think this is possible given my space

So the question that remains is, is the above example (#2), assuming the incoming duct on the right has to travel for 10' in between the leaves pointless? Should I just have the single inner leaf baffle box, and forget the outer, and just really well seal the outer leaf penetration, and use flex duct to decouple? I realize this will not be ideal, but I'd rather not add boxes if they won't do anything anyway. I can instead wrap the ducting in MLV (2 psf) to add mass to the ducting, and just have the inner baffle box for sound convolution.

[Starlight]

Yes, we can agree the principle you show in the first diagram is correct.

Your second diagram shows what you are trying to achieve in principle. Whether that is a realistic proposal I cannot say.

The 10 feet of duct between the baffle box and the main HVAC trunk does not sound good. Can you move the relevant baffle box to reduce the 10 feet to as short you can possibly make it and plan to box in (or cover with MLV) the exposed section of duct?

Having no baffle box means you would simply have two large holes in your studio wall and that is something you would really want to avoid, especially being a drummer and needing good isolation but also because it would negate much of the hard work you are doing to create an isolated environment.

At this point I am afraid that I am getting out of my depth (of knowledge and experience) and would not want to suggest anything I am not confident would work; it would not be fair to you. Hiring a pro will save you from making a costly mistake, if you cannot find a pro to give you free advice.

I don't know if the others who have commented earlier in this topic have anything to add.

[ScotcH]

Thanks for your input so far Starlight! ... by all means, if anyone else has further comments, I'm all ears! It is after all the reason I posted here

[Jag94]

I unfortunately am in the same boat as Starlight. What you are proposing seems ok to me, but I am no pro. I did a ton of research and gathered information from several forums, and then I hired THE Rod Gervais to consult on my design. He wanted a lot of money to do the design himself (which I couldn't afford), but he had a very reasonable hourly consulting fee as long as there were no major problems (which there weren't, thankfully). It may be worth an email to him to see if he can help you out. Getting the "OK" from him was such a relief and worth the money.

[lostandfound]

Hello,
my opinion, if you have calculated your baffle (outer box) correctly, the extension with the flex duct shouldn't force you to use an inner baffle, I don't see the usefulness.
I think it is very important to pay attention to the type of duct you will use, I recommend this:

https://www.has-store.co.uk/silencers/acoustic-flexible

Lucio

[SoWhat]

Greetings ScotcH,

I believe jag94 is using a single box design. Have a look at his build. Going that route MIGHT save you some aggravation (Who knows? Like others, I am no expert).

Happy New year and all the best,

Paul

[bert stoltenborg]

Source of the post Hi
I’m not sure whether there’s any acoustic difference between using flex or otherwise, I guess that comes down to where you need it to run.

Cheers
Gareth

A properly isolated flex duct works fine.
Baffle boxes are a bit of a urban myth, they look logical but in reality they are complex and have flaws.

[Jag94]

Source of the post

A properly isolated flex duct works fine.
Baffle boxes are a bit of a urban myth, they look logical but in reality they are complex and have flaws.

That's a pretty bold claim, especially since most of the studio designers/builders I've come across all use silencer boxes in some form or another. Care you elaborate on what you mean?

[ScotcH]

My plan at this point is to use a single box on the outer leaf, and flex duct from the box through the inner leaf. I think this will provide sufficient isolation based on my needs. Will update the thread with final drawings, and post some in-progress pics. We've finished the framing!

[bert stoltenborg]

Source of the post

Source of the post

A properly isolated flex duct works fine.
Baffle boxes are a bit of a urban myth, they look logical but in reality they are complex and have flaws.

That's a pretty bold claim, especially since most of the studio designers/builders I've come across all use silencer boxes in some form or another. Care you elaborate on what you mean?

Google at coulissen damper and see how professionals handle this at large scale buildings since decades instead of clinging to studio gurus .
These baffle boxes introduce a load of turbulence with all the baffles and that hinders laminate airflow.
As my friend Eric Desart would say: everything that looks complex appeals to people as better.

[Jag94]

Source of the post

Source of the post

Source of the post

A properly isolated flex duct works fine.
Baffle boxes are a bit of a urban myth, they look logical but in reality they are complex and have flaws.

That's a pretty bold claim, especially since most of the studio designers/builders I've come across all use silencer boxes in some form or another. Care you elaborate on what you mean?

Google at coulissen damper and see how professionals handle this at large scale buildings since decades instead of clinging to studio gurus .
These baffle boxes introduce a load of turbulence with all the baffles and that hinders laminate airflow.
As my friend Eric Desart would say: everything that looks complex appeals to people as better.

Those look massive. How would I fit that in a garage studio that is 15'x14'? I think that's where silencer boxes are WAY more effective. We need solutions for small spaces.

Also, silencer boxes don't introduce "a load of turbulence" if you size them correctly. When people just make a box with some baffles, and don't do the math to make sure the area of the box can handle the air volume and speed that matches the ducts entering/exiting, sure, you'll get problems. But if you do it correctly, silencer boxes can be extremely effective for small home studios... as is proven by the thousands of people who use them.