Hi everyone,

I am building my first bass trap with Isover Sonepanel which is around 8000 Pa.s/m2. Am I right to understand there is very little difference between having:

120mm panel and 320mm airgap
and
180mm panel and 240mm airgap

(attached acousticmodelling screenshot).

So in other words, why would I waste more panels making it 180mm when I can simply put them slightly more away from the wall?

Yes they are about the same. Why is one 20 mm thicker than the other. The target with 8,000 Rayls/m material is 200 mm material.

Enjoy!

Good to know, thanks.

What do you mean by "Why is one 20 mm thicker than the other. The target with 8,000 Rayls/m material is 200 mm material."

Sorry I did not pick up this part.

One step at a time. Absorber 1 is 420 mm deep and absorber 2 is 440 mm deep.

Ah I see what you mean.

So I selected the panel based on the the material I have (60mm thick), therefore I can do either 120mm or 180mm then. Based on that I tried to align both graphs to be as close a possible, and indeed one is 20mm less overall.

Overall, not taking into account other room factors, do you think it would be a good bass trap for the amount of space I am willing to sacrifice on by back wall (max ~400mm)? I will make multiple of them. Or there is something better what I am missing?

I also want it to be sort of modular, so I can take it out and move to another house if ever needed, therefore I am not considering something very thick like 40cm of fluffy.

Absorber 1 is better. It is a good design for your application.

great!

One more question on my mind - is it good idea to simply put such panels along the whole back wall, including corners, or it's much better to put triangle shaped bass traps (in corresponding size) into the corners instead?

Both, imho. Deep panels for back wall and triangular "chunk" style for the corners. If the corner traps are very thick, approximately 250mm+ the filling should be lighter, like fluffy attic insulation. For a trap like you mentioned 180mm thick but flat, straddling the corner with an air gap behind is probably better than just cutting 180mm into a triangular shape. The triangular trap 180mm thick right up to the corner, would be much narrower and so have a much lower volume of absorptive material than a 600mm wide trap 180mm thick with an air gap behind it (not sure if that math works out exactly, but you get what I'm saying).

Hot Sauce gave a great answer!

Learned a lot from reading your posts over the years, Avare! And others on this great forum.

I have followed the thinking that says lighter and deep is better for bass traps. I have even been considering the option of making truly deep, say 3 feet deep, bass traps filled with polyester filling and batting. That would certainly satisfy the health paranoid people out there who don't want to put 500 cubic feet of fiber glass in their room.

Ok I see. So I realize that triangular chunks are better in the corners, but I am trying to figure out how much better. It's much much easier for me to make couple of these 180mm panels and put them all along the back wall, compared to also making two additional triangular bass traps just for the corners.

So for example if triangular chunks in corners will only increase effectiveness by 5%, then I would not bother, but if it's 30% different, then i will.

You are missing something. Hot Sauce wrote:

There are a couple ways to think about corner traps, imo.

You can think about it in terms of the total volume of absorbent, which for a rectangular or triangular corner panel is easy enough to calculate. But this does not take into consideration the air gap, which ties into the other way of thinking about it --

The total amount of room volume you are giving up to the treatment when all is said and done, including both absorbent and air gap. The air gap can help to make up for a thinner panel to a degree, though filling the gap with more absorbent is better in almost every case as far as I know. But this also ties in with materials selection, because if you do fill the corner, thus making a much thicker trap, you will want to alter your materials selection and go for the fluffier, less flow resistive stuff - 5000 pa.s/m^2, which is more optimal at that thickness.

If you choose to leave an air gap and have a panel that straddles rather than fills the corner (180mm thickness you said), then that is firmly in the territory of the more flow resistive material, 10000 pa.s/m^2, being optimal.

That said, a trap that fills the corner made totally with 10000 pa.s/m^2 insulation is still better than one that straddles the corner and is 180mm thick with an air gap. It is a bit less effective than an equivalent trap made with the fluffy stuff, though that is also largely dependent on what the problems in your room are.

So I guess the question is, how simple do you want to keep your build? Are you willing to buy multiple material types? You mentioned it is much easier for you to just make the same traps for the back wall and corners. If that is the case then select a 10000 pa.s/m^2 filling material and go for 180mm thick, but make the corners are straddled rather than flat. The air gap does help in a significant way. Without an air gap, absorption falls off rapidly below 100Hz.

Me personally, if I am giving up space to a trap I figure I might as well make that space perform its function as well as it can, so I choose to fill the gap fully. If materials or build complexity are concerns then a straddling panel with an air gap is viable, just not as ideal. If the choice for you is between making a 600mm wide, 180mm thick panel that straddles the corner, or a chunk that is equally wide but fills the corner, I would go for filling the corner, IF you can afford the materials and IF you are willing to use different filling material for the chunks. It depends on what specific problems you are attempting to address, but generally I would say that the difference in effectiveness would be significantly more than 5%, but depends on the target frequencies.

Oh, and if you were thinking you would just line panels up along the back wall without straddling the corner - that is by far the worst option - definitely straddle the corner.

I'm not sure of your being jest or serious, but I would be interested in actually doing corner bass traps like this in my room! I would prefer it over fiber glass any day. How would I create this large 250+ corner bass trap w/ polyester filling & batting?

small size Corner treatment as the only thick thicker treatment in a room will not solve the bass problems.
Treating thick and flat over the entire back wall will outperform small superchunks.
If you have a room that is, say 3,5m wide, superchunks will cover 24% of the width, but can only be considered thick enough to absorb bass in the center of the traps. full wall treatment will of course cover 100% of the width.(and height)

If building corner traps on the front to sidewall, build them like this:
30degrees from outer left and right 1/3 of front wall all the way out to the sidewall.
Then you can place speakers close to those traps.(you can also build the center 1/3 flat at least 8")
My recommended Treatment depths sidewalls: 1/12 of the length between walls.
treat the sidewalls to parallel with LP(at around 37-38%)
between the walls.
back wall/ceiling 1/10 of the length.

No problem using glass wool(avoid rock wool) but you can cover it with a thin layer of polyester wool(dacron) before fabric.
you can find polyester wool in a fabric store.

Why do you say avoid rock wool? I’ve had much worse experiences with fiber glass. I know some people can be more sensitive to either though so it’s a good idea to see how one tolerates the stuff before filling the room with it.

Also I wasn’t jesting about a pure polyester trap, the only problem is I’m pretty sure it’s a massive fire hazard. In any event the way one would build it if they wanted to take the risk is pretty similar to a normal corner trap build. Make a frame, loosely fill it with polyester stuffing and wrap it with the polyester batting (Dacron, as above) so the surface is even. You can also use layers of the Dacron as support platforms on the interior of the trap to keep the stuffing from sinking too much. Just cut it to shape, staple to frame, and fill with stuffing. Hypothetically such a trap 900mm or 3 feet deep would have a high amount of absorption down to like 30Hz, if I am remembering correctly. On the other hand, 3 feet is enormous.

Thank you! I appreciate the reply and details. I was searching on YT, but could't find something similar, except a video of using towels!

By 900mm/3 feet deep, is that measuring from the center of the corner out to the center surface of the triangle? or is it 900mm across the outward triangle surface from one wall to the other wall?

I mean from the trap face to the back of the corner, but a trap like this, if a true triangle, would also be extremely wide. Wider than 3 feet for sure. A soffit trap could be an option but the absorbent volume would be much less.

I haven't made any of these. However I have included a layer of this stuff in some clouds I made. The clouds are 6 inches thick total, 3 inches of polyester (which I believe is about 2000 rayls/m) and 3 inches of 10000 rayls/m material. They are spaced pretty far from the ceiling so there was corresponding large dips in the absorption. I was modeling different clouds in the multilayer absorber calculator and it seemed this was a better option than 6 inches of pure 10000 rayls/m material, which, while taking care of the dips in absorption due to distance, also reduced the absorption below 200Hz in a significant way. However I can't say for sure that it behaved exactly this way in the real world since after all, it is just a calculator. But I would think the predictions are at least somewhat accurate. In any event the clouds did help the low frequencies substantially.

It is equivalent to 2 45°-45°-90° triangles with 2 of the non hypotenuse sides togther. So twice the depth.

Once upon a time I had those formulas memorized. I suppose I can learn them again, and they are very simple. After all, I have brushed up on quite a bit of mathematics since starting to train as an electronics technician.

Great! What is so sad is how many people want to learn acoustics but are terrified of mathematics. It is an integral part of understanding acoustics.

I certainly want to learn more. I find some math intuitively easy, like geometry and algebra. I had a lot more difficulty in precalculus, but I wasn't really interested in it at the time. When I attended music conservatory (where most students loathe math), the math requirements for graduation were exceptionally lenient. Even after 10 years, it does come back with a bit of study.