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A celing-wall bass trap absorber in progress
Old 3 weeks ago
  #1
Here for the gear
 

A celing-wall bass trap absorber in progress

Here is my celing-wall bass trap absorber in progress.

I made it so it would angle out into the room, with some flat face, so it picks up ablique angle waves, and so the insulation thickness will be of 300mm, with 50mm air behind. I didn't want it square because that doesn't seem as attractive. The angling on the inside allows for some air space, and to be away from crown molding that is already along the the wall-ceiling-edge.

The frame is made from 24mm x 150mm fence pailings, cut at 45 degree angles, on the drop saw (the inside cuts finished with a handsaw), then two halves glued; plus, metal corner beading screwed on.

The size, I determined by seeing how much space I generally had above our door frames. It looks like, from the http://www.acousticmodelling.com/porous.php that 400mm or 500mm depth would be even better, but it depends on the room you have to work with.

I want to use Knauff acoustic glass wool, because the the depth is 300mm. Normal density is 14 kg/m3, which I think is air flow resistivity of: 5 kPa·s/m² = 5000 Pa·s/m² = 5000 rayls/m
(Air flow resistivity for Isover Sweden, http://www.johnlsayers.com/phpBB2/vi....php?f=3&t=7014)

I would appreciate any feedback. Am I on the right track?

I'm working out how to make corners, before I finish it.
Attached Thumbnails
A celing-wall bass trap absorber in progress-ceiling-wall-panel1.jpg   A celing-wall bass trap absorber in progress-ceiling-wall-panel2.jpg   A celing-wall bass trap absorber in progress-calc.jpg  
Old 3 weeks ago
  #2
Lives for gear
 

Nice workmanship, but there's an easier way. The photos below show how I normally do horizontal superchunks. The idea is to maximize depth and volume as much as possible. If you don't have a lot of space, then the triangles can be made "uneven", in the sense that they extend further along the ceiling than they do down the wall.

Quote:
I made it so it would angle out into the room, with some flat face, so it picks up ablique angle waves,
There's no need to do that. Obliques are not the biggest problem: axials are. Obliques are several dB less intense than axials or tangentials, and also higher in frequency. But all of them are basically still very large pressure waves that sort to "wash over" or "pump through" the absorber. Angling part of the face isn't going to improve the trapping of any of them. It also makes the effective depth for non-normally incidence smaller.
Quote:
and so the insulation thickness will be of 300mm, with 50mm air behind.
The air gap does not help to improve absorption. All it does is use less material to reach the same frequency. If you want to cut that off to better fit around your molding, then that's fine, but it does not improve performance.

Quote:
I didn't want it square because that doesn't seem as attractive.
Then make them triangular!

- Stuart -
Attached Thumbnails
A celing-wall bass trap absorber in progress-superchunk-horizontal-corner-trap-detail-enh.jpg   A celing-wall bass trap absorber in progress-cd_k-wall-top-superchunks-horizontal-zm-sml-enh.jpg  
Old 3 weeks ago
  #3
Here for the gear
 

Quote:
Originally Posted by Soundman2020 View Post
...If you don't have a lot of space, then the triangles can be made "uneven", in the sense that they extend further along the ceiling than they do down the wall.
Much appreciated Stuart. I gain depth by extending out the bottom edge, don't I? because i am limited in places by door frames, but, yes, the top edge could be extended on a lesser angle, I have room for it, reaching out further into the ceiling - then if I reached out further to the ceiling and still butted the ends like I have, I would be getting more depth still (+150mm). I hadn't thought about ceiling clouds, but one could butt up against an angled edge.

Quote:
Originally Posted by Soundman2020 View Post
The air gap does not help to improve absorption. All it does is use less material to reach the same frequency. If you want to cut that off to better fit around your molding, then that's fine, but it does not improve performance.
I agree the air gap doesn't improve it...thinking. Thinking I could leave the back open from final material wrapping, so the glass wool can puff out into any air space. Part of my thinking is to make these portable. In my last house I made permanent fixtures that I had to leave behind, so I want to make very portable solutions.

I will rework the design, given a couple of weekends ... still thinking. Thanks again for your comments.

Warwick
Old 3 weeks ago
  #4
Lives for gear
 

Quote:
I hadn't thought about ceiling clouds, but one could butt up against an angled edge.
That might be necessary, depending on how you hang your clouds, and the dimensions of the room. It's usually a good idea to hang he cloud at an angle, with the front edge (over the speakers) lower down and the rear edge (over the mix position) higher up. If you do that, then it should be able to clear the superchunks. Of course, if you have a low ceiling then that might no be possible, but for normal ceiling height it's good to angle the cloud. That helps in several ways, and if you make the cloud "hard backed", then one of those ways is by redirecting sound away from the mix position towards the rear wall, at least for some frequencies. It also helps with flutter echo in the vertical plane, and perhaps also helps a bit with vertical modal issues.

- Stuart -
Old 2 weeks ago
  #5
Here for the gear
 

corner join

I tried the alternative angled wall-ceiling trap, to pass the-wife-good-looks-test, but it's a bit small to get low frequecies. Stuart, abiove, suggested making them triangle maybe extending the top edge:

Governing space limitations, I am wondering what to do. Okay, so let's get sidetracked, as I often do (but still learn something):

a) The BBC D2 (REF: BBC Engineering Guide to Acoustic practice. 1990). See pic. I was thinking, hmm maybe I could adapt this somehow into my design. Nope. A good idea for later bass trapping, but too heavy anyway for wall-ceiling traps.

b) RPG type BAD panel. Like hanging them as angled plates. Nope, not designed for corners, and anyway they rfelect which I dont want for vocal recording.

Okay, back to reality, back to Stuart's advice (see above). See (pic) of new side frame design for triangle, ceiling length a bit longer, to get that extra bit of density. [I'm not going to worry about doorframe or window frame height. maybe for those parts I'll use my original smaller design or rely on ceiling clouds]. The short side is 17", it gives me a centre depth of 350mm and 400mm angling in off-centre from the higher side. That's going to be okay to get at the low frequencies.I used 31.6 degree setting on the drop saw for the face angles. All wood is cut from 25mm fence pailings. Needs, I think some more reinforcing in the corner, then glued, and I can make three of these per section.
Attached Thumbnails
A celing-wall bass trap absorber in progress-img_2524-corner.jpg   A celing-wall bass trap absorber in progress-d2-bbc-engineering-guide-acoustic-practice-.jpg   A celing-wall bass trap absorber in progress-d2-chart.jpg   A celing-wall bass trap absorber in progress-03-make-top-ceiling-length-longer.jpg  

Last edited by romus; 2 weeks ago at 08:01 PM.. Reason: Added a questions about adding grid
Old 2 weeks ago
  #6
Lives for gear
Quote:
Originally Posted by romus View Post
not pass the-wife-good-looks-test,
In the DIY speaker building world they call it WAF- Wife Acceptance Factor.

I saw one post where a guy suggested that the ultimate speakers were 3 way horns with the largest ~80hz (which is like 8' x 10' or larger) made from 1/2" plate steel covered in tar! This led to everyone trying to figure out if WAF is linear or exponential and what the lowest possible WAF rating is...
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