Trying To Make A Few Decisions On Walls

[thedavidlim]

Hi all,

I started this project a couple years ago and am now circling back. Having finished framing/plumbing/powering the rest of the basement, I'm now allowed to think about a mix room again

My questions are about treatment, not about isolation. I don't really have any isolation goals and am not sealing off the room to be airtight or anything like that. I'm not concerned with sound getting in/out since I don't have the money to do it right at the moment and my wife isn't worried about it

As you can see in pics, I'm in a corner of the basement, and the room is 20'6'L x 10'6"W, with a 7'6" ceiling. The front and left walls, when facing the monitors, are cinder block and the back and right walls are alternating studs on 2x6s, just to make the walls a little thicker and stop a little bit more sound than "normal".

1. Does my start at a design make sense? The left/right angled wall would be slotted, and are angled around 6º, which works out with my ray tracing also. Corners right now are super chunk, although I'm considering just 4" panels top-to-bottom because the electrical panel is behind the left trap and I need to be able to get to it, which is also a big reason I'm not building soffits for my speakers. In addition, I'm planning to put angled panels in the wall-ceiling corners on both sides and the front, and the rear wall will be a diffuser or slot wall in the middle.

2. I'm unsure if I should put gypsum on the left rear wall, or not. If I do, it would be symmetrical with the right wall, which will be gypsum, and then I could put treatment on top, but I'd also thought about leaving the studs open and putting cloth over them with the insulation behind it. I would then put absorptive treatment on the right wall as before, but I'm a little worried there would be too big a difference in the sound back there in that case, since the treatment wouldn't really be symmetrical. The other thought was a slot wall on the left instead of gypsum or cloth, since it'll be 3.5" of insulation either way.

3. I'm also curious if regular fluffy is ok behind the slotted walls, or if there's a big benefit to Roxul back there? I guess the same question applies to the super chunk corner traps.

Studio Ideas.jpg

Thanks for everything!

[Gregwor]

Your image isn't showing up for me!

Greg

[thedavidlim]

Interesting, I’m looking at it on my phone right now. I can try to repost is evening. Thanks!

[thedavidlim]

Try this.

[Paulus87]

Hi,

There's a few things you could do to improve your design;

1. You can still flush mount (soffit mount) your monitors and have a removable panel or door in order to access your consumer unit.

2. Though you say your angled side walls at 6 degrees works out with your ray tracing, I am not seeing it. It looks like your head will still receive many reflections from the side walls as the angle is too small. Can you upload pics of the ray tracing you've done so we can take a look?

3. What's the purpose of the diffuser on the front wall between the monitors? First off diffusers work best when you direct sound at them which is why they're usually found on the rear wall behind the listener or in large rooms on the side. They are sometimes found on the front if you have a surround setup, but again that's usually in large rooms. A rule of thumb is that any diffuser should be at least 10' away from the listening position in a control room if you'd like an accurate representation of what you're hearing from the speakers. Diffusers smear and skew the image at short distances. I'd remove the diffuser altogether and rely on absorption and perhaps carefully placed slats in certain areas.

Those are the things I'd take a look at first. To answer your other concerns:

- there are calculators you can use in order to estimate what type of insulation, how thick it should be and where best to place them. Google "multi layer absorber calculator" and you should find one, that along with a room mode calculator should be enough to get you pretty good results. But in general, use light density fluffy insulation for thick bass traps and any panels over 4", if below 4" you can use Rockwool. There is not much use for Rockwool (Roxul) or other rigid dense insulation at a thickness greater than 4", even 4" is too thick in most applications and 2" Rockwool behind fluffy insulation could be better. This is to do with the gas flow resistivity of insulation products which is measured in pascal seconds per cubic meter (Pa.s/m3) or rayls. The lower this number the easier air can flow through the fibres and the better the absorption co-efficient for low frequency becomes the thicker you go (up to a point). There's a cross over point where fluffy insulation starts to surpass the equivalent thickness of Rockwool, which is roughly around 4" - 6" depending on the GFR. Also, in my opinion you can discount anything below 0.6 on the absorption co-efficient scale, atleast 0.7 and above is really what you're aiming for for good absorption.

People like to use Rockwool because it is easier to build with since it keeps its form fairly well and you can stack it easily, but you can achieve similar results by building frames to hold the fluffy stuff.

So to summarise, for thick bass traps and corner super chunks use light density fluffy insulation. For mid frequency absorbers that need to be thinner (4"), you can use Rockwool but don't expect them to be broadband.

- regarding drywalling one wall and leaving the other; if isolation is really not a concern then I would take the drywall off both walls (providing they both have a rigid backing of some sort already) so that they both have their studs exposed. We call that an inside out wall around here and it has the advantage that you can use the stud bays to hold the insulation for your acoustic treatment which can then be covered with fabric. This is especially useful if you have a low ceiling as you can use the bays between the joists or rafters which are thick, so you can get a nice lot of treatment up there. Doing this also increases your room volume which is always a good thing. So if you can, take the drywall off that and then treat both of those walls with insulation which can be covered with fabric and some slats if you wish. Whatever you decide to do though, symmetry is best. You want your control room to be as symmetrical as possible from left to right. Some people suggest it only matters at the front of the room, from the listening position to the front wall, but in my opinion in small rooms the rear symmetry is just as important unless you have some serious treatment on the sides and rear where it is no longer an issue due to almost all reflections being dead, but that takes up a lot of space.

Hope this helps,
Paul

[thedavidlim]

Thanks for the reply!

To reply in numbered order...

1. To be up to code I have to have a working space of 30" in width and 36" in front the electrical panel. If the soffit is as massive as everyone says it needs to be, and I don’t mean just size but the amount of framing and insulation, then having clearance there won’t really work or be up to code with just a service door or panel.

2. I can pull up my ray-tracing and post it, but now you make me want to recheck it, so I may do that first.

I’m really debating having splayed walls there at all, instead just putting absorptive panels up at reflective points.

3. Good advice on the diffuser, I’d forgotten that. My (inaccurate) thought was to avoid just a flat surface there, but I’ll make it absorptive or put slates if that’s too dead.


As far as drywall and isolation, I should probably clarify my previous statement slightly. It not that I don’t have ANY isolation concerns, but am not able to (again, for mostly financial reasons) fully soundproof all walls and ceiling, so am not going to worry about it past normal insulating and drywall on both sides of the wall. That said, I hear you on symmetry and will put sheathing on the studs covering the block wall too. I’d thought about wood planks there, for aesthetics, instead of drywall. Will the density difference really matter if both are reflective surfaces?

As always, thanks!

[thedavidlim]

Here's my initial attempt at ray-tracing after moving the corner chunk bass traps and seeing what it would look like to push splayed walls up to the front. The are still at 6º, currently. I'd put bass traps in the corners still, but removable or hinged.

Am I doing this right?

[Paulus87]

Here's my initial attempt at ray-tracing after moving the corner chunk bass traps and seeing what it would look like to push splayed walls up to the front. The are still at 6º, currently. I'd put bass traps in the corners still, but removable or hinged.

Am I doing this right?

Yes you are doing it correctly, but you need to remember that there are infinite rays between the rays you have drawn here... so it is clear to see that your head will be right in the middle of some first order reflections. What you need (if you're aiming for a RFZ) is an actual area where there are no rays being reflected all the way around your head and ideally the whole width of your workstation/console.

Usually you'll need much bigger angles than the 6 degrees you've drawn here - I think you got 6 degrees from other posts on this forum which talk about 6 degrees being the minimum angle needed in order to prevent flutter echo (2 walls angled at 6 degrees or 1 wall angled at 12 degrees) but this is a separate issue to creating a RFZ.

Due to the width of your room you may actually be better off using broadband absorption on your first reflection points, as I don't think you have enough space to achieve it via geometry. You could keep your 6 degree splayed walls if you wish and then make a section of them fully absorptive, where your first reflection points are. Another option could be a CID design for your side walls, that could work really well if designed properly.

I also realised you could actually have inside out walls for your side walls providing they both have a rigid backing. So you would build a timber frame on each wall and then in fill the bays with insulation and cover with fabric/slats. Your left wall's rigid backing would be the blocks, and your right wall's rigid backing would presumably be drywall (that will be on the face of the wall which is facing the room next to your studio) you would probably want to make that wall quite beefy, maybe 3 layers of drywall to help make up for the difference of mass between the two walls, or if you do not need isolation between your studio and the room next to it then it is not so important. Since you are limited in what you can do isolation-wise than I would not spend much time and money on it as the isolation will only be as good as its weakest link.

Hope this helps,
Paul

[thedavidlim]

Ah, that makes sense. I definitely got the 6º min from other posts. I was thinking about larger angles when I was ray-tracing, but unless I pulled the whole thing back from the front wall I would hit the service panel, so I think you're right on with just using first reflection absorption. And that's fine.

The right side wall, as described in my OP but not really visible in the Sketchup, is a 6" staggered stud wall, and the other side is a staircase built against the wall. I wouldn't be able to beef it up unless I did it all in the stud wells, so I'll probably fill it with insulation and drywall as usual, maybe 2 layers on the inside to keep what isolation I can, then use wood paneling on the left side over the blocks for symmetry.