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RE: Super Chunks with a twist

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In Reply to: RE: Super Chunks with a twist posted by johnvb on December 12, 2010 at 09:04:08

Filling the corner solid (chunk) is not a substitute for having enough front surface area. But the size you propose is pretty good. A rounded face will not do much for a corner trap, even if the front is reflective, because the corners of a room are not usually reflection points. But a thin reflecting surface will help increase bass absorption. Any thin material will help, such as Kraft paper or contact paper etc.

--Ethan

Follow Ups:

RE: Super Chunks with a twist - JimBop 11:46:04 12/12/10 (1)
How/why does a thin reflecting surface help increase bass absorption?

JD
- RE: Super Chunks with a twist - Ethan Winer 09:45:01 12/13/10 (0)
  > How/why does a thin reflecting surface help increase bass absorption?
  
  By acting as a damped membrane. I can't explain the science completely in a few words, but clear proof is in this article:
  
  Density Report
  
  --Ethan
RE: Super Chunks with a twist - johnvb 10:24:05 12/12/10 (9)
Thanks Ethan. In my case, due to the way my dipole magnepans are placed in the room, they actually do shoot part of their rear wave into the front corners.

I also plan on trying some of those diy "room lenses" made out of PVC tubing, for some added diffusion, They are said to work best in front of a reflective surface.

So anyway, that sounds good, I was hoping I wasn't too far off the reservation :^)
- RE: Super Chunks with a twist - Ethan Winer 09:42:47 12/13/10 (2)
  > they actually do shoot part of their rear wave into the front corners. I also plan on trying some of those diy "room lenses"
  > made out of PVC tubing, for some added diffusion, They are said to work best in front of a reflective surface.
  
  If your speakers send mid and high frequencies to the rear, then you want real diffusors, or absorbers that work at those frequencies. A "room lens" is not a diffusor, and it's not large enough to do anything useful IMO. This video may help:
  
  All About Diffusion
  
  --Ethan
  - RE: Super Chunks with a twist - johnvb 07:18:08 12/14/10 (1)
    Very informative video, now I have to watch all of them :^)
    So if I treat the outer curve of the bass trap I described above with a thin membrane, would that be considered sort of a combination of a bass trap and "poly diffuser", or does that only apply when multiple curves are employed?
    As for as the back wall, I'm unfortunately stuck with a desk/bookcase as diffusion for now, only because this is supposed to be a home office (although not much gets done in there other than listening and net surfin :^)
    
    Edits: 12/14/10
    - RE: Super Chunks with a twist - Ethan Winer 10:55:41 12/14/10 (0)
      Yes, if the membrane is thick enough to reflect down to maybe 1 KHz, and the curve is severe enough, that will give some dispersion to sounds that arrive at the front face.
      
      --Ethan
- RE: Super Chunks with a twist - David Aiken 12:53:30 12/12/10 (5)
  The room lens provides diffusion via 2 means. First, the curved pipe surface reflects over a wider angle than a flat surface does. Second, sound passing through the gaps between the pipes is diffracted as it emerges on the other side of the unit�that means it spreads out over a wider angle. The diffraction works for sound travelling in both directions. Placing the unit close to a wall results in sound passing through the spaces between the pipes to the wall being diffracted and spreading over a wider wall area and being reflected back into the room over a much wider angle than would otherwise occur and sound being reflected from the wall through the spaces is diffracted and spread into the room over a wider angle than would occur without the unit. You would need to experiment with distance from the wall in order to fine tune the result to your tastes.
  
  I experimented a bit with DIY room lens units some years ago and posted some of my results in Tweakers Asylum. I used Jon Risch's instructions for building the units. One of his comments was that a 4 pipe unit would work better than a 3 pipe unit which it does. Eventually I experimented with placing several units side by side and angling some of the units relative to the others. That lead me to building an 8 pipe unit with the pipes placed in a pattern determined by a quadratic residue formula so the pipes were placed at different distances from the front of the base in something like a W-shape. That seemed to give me better results than I got with 3 x 3 pipe units placed side by side, even with a bit of experimenting on the angles the units made to each other.
  
  If you still have the 11/6 x 15/6 x 8 room you mentioned, my feeling is that it may actually be too small to benifit greatly from diffusion. Diffusion needs space in which to develop and you need to sit a certain minimum distance from a diffusor in order to get a smooth response from it. That minimum distance depends on the design of the diffusor but 10' has been suggested by one manufacturer. Ensuring any diffusor you use is 10' from your listening position is going to limit placement to the front wall of your room if you use a short wall speaker placement. I don't know how that will work with dipoles like your Maggies but when I tried that sort of placement with room lenses and box speakers in my room, I got a presentation that delivered a big soundstage but broadened the individual images within it, making singers sound like they had mouths 2' wide for example. I really liked the effect with symphonic music but I hated it with small group music and singers and most of what I listen to is small groups and singers. It's certainly worth while experimenting with diffusion but I think that absorption works better in a small room. I know others think differently and not everyone likes the same sort of room treatment result. Definitely give it a go if you're interested but I know that in a room your size my preference would be for absorption rather than diffusion every time.
  
  David Aiken
  - RE: Super Chunks with a twist - johnvb 16:50:15 12/12/10 (2)
    Thanks for the detailed explanation, David. I was recommended the room lenses from some folks over at the planar asylum. Appears they use them mainly to treat the rear wave, and also the first reflection points. I am still using the aboved sized room, so we'll see what they can do for me.
    I have 60' of leftover 2" (ID) PVC pipe from a plumbing remodel, so just need to find some free time to build them :^)
    If I go with more than 3 pipes per unit, what would you recommend for the top and bottom spacing of each?
    - http://www.audioasylum.com/forums/MUG/messages/16/165181.htm (Open in New Window)
    Edits: 12/12/10 12/12/10
    - RE: Super Chunks with a twist - David Aiken 21:20:24 12/12/10 (1)
      Just go with the recommendations in Jon Risch's instructions. If you do more than 3 pipes per unit, then just repeat the spacings for one of the pipes. As far as the stuffing goes, either repeat the stuffing for the pipe with the stuffing about midway in the pipe or repeat the stuffing approach for different pipes and spread the additional pipes around the larger units randomly.
      
      David Aiken
      - Thanks...nt - johnvb 02:59:06 12/13/10 (0)
        
        In Reply to: RE: Super Chunks with a twist posted by David Aiken on December 12, 2010 at 21:20:24
        
        .
  - RE: Super Chunks with a twist - JimBop 15:31:46 12/12/10 (1)
    2 Questions:
    
    Considering your comments about room lenses and curved or round surfaces, why are most diffusors built from square or rectangular materials?
    
    How critical are the lengths of the DIY room lenses? I'd like to experiment with these, but would prefer them to be a bit shorter than the designs I've seen. Something around 48"-54" would provide better visual balance (and WAF).
    - RE: Super Chunks with a twist - David Aiken 16:13:33 12/12/10 (0)
      "Considering your comments about room lenses and curved or round surfaces, why are most diffusors built from square or rectangular materials? "
      
      Because there is more than one way to disperse sound over a wider angle. Diffusors like the various QRD designs can achieve better dispersion than simple curved surfaces. If you're going the DIY route, however, it's easier to construct a simple curved surface from a material like a lightweight plywood than it is to construct a QRD type diffusor. The curved unit is also going to be a lot lighter and easier to mount on a wall than a QRD type device, or easier to move around the room if you're going to leave it free standing against the wall.
      
      "How critical are the lengths of the DIY room lenses? I'd like to experiment with these, but would prefer them to be a bit shorter than the designs I've seen. Something around 48"-54" would provide better visual balance (and WAF). "
      
      The room lens does 2 things, diffusion and some bass absorption because the pipes act as Helmholtz resonators. Length isn't critical for the diffusion function though it will to a degree affect the bass absorption because it will modify the resonant frequency of the tube. Having said that, Jon Risch's comments were that you really don't get much bass absorption from the tubes so if you're primarily interested in the absorption then reducing the length to 48"-54" is fine. As I said, 4 pipe units will be more effective than 3 pipe units for diffusion, and even more pipes will help more. If you're going to go for a spread of 6 or more pipes, I'd suggest multiple 3 or 4 pipe units side by side and play around with how you angle them in relation to the wall and each other. I think you'll get a bit better result that way. I think more complex pipe layouts like my QRD version can work even better but I built only one and I definitely haven't tried playing around with a variety of different multiple pipe layouts in order to try and find out what works best. I do think it's possible to get better results than the simple straight line placement pattern used in the original 3 pipe design but unless you simply want to copy the layout I used I'm afraid you're on your own and you're going to have to run your own experiments. If I was going to experiment with a 3 pipe layout that wasn't in a straight line, I'd probably start by considering duplicating the layout of the 3 vertical pieces in the Shakti Hallograph to see how that kind of placement and angling worked.
      
      David Aiken

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