 
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
|
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
In Reply to: Re: DIY Roomlens Questions posted by Sampsa on June 08, 2004 at 20:10:31:
Greg Weaver and others use the "noodle lens" format for Maggies. Just a foam tube on a base behind them. Those who like the noodles are using only the diffusion and diffraction at most, but seem to like this with those planars. You might want to experiment with this as it's extremely easy and cheap to do.Here's what I recommended to David Aiken when he was experimenting: use PVC pipes as usual, but put them on a simple wooden base. Screw a PVC flat pipe cap to a 3"X3" or so wooden piece of 2" lumber; friction mount the pipe on the cap/base. Make each one separately. Then use several to move them around and experiment with different placements and configurations of spacing. True, this doesn't provide for stuffing, but that can come later when you've found the ideal configuration for you and you remove the pipes and put them on a proper open base.
He swears by his quadratic and root configs and they're worth your trying...
Follow Ups:
The problem with the noodles is that they come in horrible neon colors and there's no simple way to paint them without losing the absorption they also provide. So I'm going to go with PVC pipes.That suggestion for finding the placement sounds good.
I read about David's root configs, but they would be too big and cumbersome in my small room - from a visual esthetics point of view. But I might consider four pipes per lens to cover better the back of the Maggies.
I am intrigued with David's basic premise (the math is his specialty, not mine!) that varying the front/back spacing can make a useful difference. If you're going with 4 pipes, Jon recommended making the 2 outer pipe spaces the same and the inner one different (use the spacing he recommends). Then consider moving the outer pipes forward so you're making a sort of open U config when looking from the front. You can do this easily with the method I mentioned above. Then try moving one of the outer one's more forward so it's an uneven U. This might give you some idea of what David has been playing with. I'd be very interested in your results.I recall Jon or David or someone telling me originally that I could mount a set of these horizontally on the wall above my piano and between the speakers and get another effect. You can try this simply by turning a fixed pipe array on its side and propping it up at various heights as your center set.
Lots of stuff one can do with these babies!
Why should the two outer spacings be the same? Wouldn't it help the diffaction to cover a broader range if they were all different?
That's what Jon suggested to me at the time. I see no reason that your idea wouldn't work well too.
Actually, I was thinking of making the narrowest gap about 2/3", so that 20 kHz would still be diffracted 45 degs. When that reflects from the wall behind the speakers, it would cover the whole width of the room at the listening position.I'll have to use more than 3 pipes, since I want to diffuse the whole backwave of the 17"-wide MG12s. The standard 3-pipe model is about 8 1/2" wide, in total. Hmmm... But if the roomlens won't do anything to freqs below about 800 Hz, I'll have to worry about only the sound coming from the tweeter (crossover at 600 Hz), and can put the roomlens behind that alone.
The only thing is that if I use more than 3-4 pipes, I have to stagger them some how (maybe quadratic residue a la David Aiken), for otherwise the waves reflected from each will combine by Huygens' principle, resulting in less diffusion. But then making the gaps right for the diffraction is another question.
Maybe I should just use thicker pipes and close them so that I don't need to worry about Helmholtz resonances.
Sorry for this stream of consciousness writing...
If you try something along the lines of my quadratic residue or primitive root layouts, the width of the array is simply the width of a single pipe multiplied by the number of pipes you use. There are gaps in the array, but they result because the pipes are staggered in depth rather than in width, and the width of the gap varies from gap to gap because the variations in depth aren't all uniform.As far as space goes, the problem becomes the depth of the unit. If you don't have much space behind your Maggies, you probably wouldn't fit a unit in. The smallest quadratic root layout I have a formula for is for 6 pipes with a depth equivalent to 5 pipes, plus a bit extra for the base of the unit to provide some support. Using my spacings, an 8 pipe unit has a depth of 5 pipes and an 11 pipe unit has a depth of 10 pipes - basically depth will be 1 pipe width narrower than width. The quadratic units will have a symmetrical diffusion pattern.
The Primitive Root units will have the same depth as width, but a slightly different number of pipes and they have an asymmetric diffusion pattern. If you were going to use them, you'd want to build mirror image pairs and you could then experiment whether you got better results with scatter to the outside of each Maggie or to the centre.
You can reduce the depth of both sorts of units by reducing the depth spacings for each pipe. You could halve the depth, for example, by using depth intervals of half a pipe diameter instead of the full pipe diameter I used. This will narrow all of the gaps by a bit more than half so the lowest frequency for effective difraction will drop. You could drop the depth even further, but you're going to lose effectiveness as you do so because you're closing the gaps up. I haven't tried any depth interval other than the one I'm using, but if I was going to I wouldn't reduce it to less than half a pipe diameter for that reason. I also probably wouldn't try increasing it beyond a full pipe diameter because I think the gap widths might become too wide.
You can also use the standard pipe side by side layout and keep adding pipes if depth is an issue. There's no limit to the number of pipes you could add this way. There are 2 different gap widths in the standard 3 pipe array and I'd just keep alternating those 2 widths. There's no reason not to build an array the full width of a Maggie if you wanted to, and you could place it so that it was completely obscured by the Maggie so it simply was 'invisible' most of the time. The only problem with increasing width is going to be that you'll want to increase the base depth a bit for stability. You could do this simply by extending the support points front and back with legs that extended out from the standard depth base.
David Aiken
Thanks! What I'm worried about with putting a large number of pipes in the same plane is that their reflections would combine into one waveform according to Huygens principle, resulting in mostly reflection rather than diffusion. I don't know if 4-8 pipes would yet do that, but ...
Looking at all your posts, it appears that you have one hell of a long weekend available and are going to spec out every conceivable acoustic treatment on the board! Slow down, bro!You need to test out one effect/setup at a time to do this properly. Figure out your worst problem (reflection, echo, bass nodes, etc.) and work on that till you're satisfied. Then attack the next in line. If you do it all at once, you're going to make a lot of work and not know what's working properly and what isn't.
Actually, I've kind of done some testing already and realized that:a) I need to block the open doorway to the hallway.
b) I need diffusion, and lots of it, not absorption behind the speakers, and probably also elsewhere in the room.
c) Absorption in the upper corners might be useful.So now I'm just trying to figure out the most effective and cheap way to accomplish that.
I'm not so much trying to solve any particular problem (though there are a couple: harshness at around 3 kHz due to backwave reflections), but rather trying to make my room overall sound good with my speakers.
No, I don't have one very long weekend to build everything, but I want to understand first and build then slowly over time. And regarding the number of posts, this isn't the only forum where I've been posting... :)
Sampsa,David is giving you good advice on that doorway. His situation may be different from yours (my open hallway is similar and different), but the basics are there. If it's not a WAF or home resale issue, experiment with a door or absorption or any combination.
Yes, I've seen your posts all over here. I'm guilty of same style of rapid absorption of new knowledge at the expense of my friends' ears. LOL Did the same here on numerous occasions.
Idea is still to find a single issue and try to solve that first, even it you aren't sure which. YOu say you're not trying to solve a problem, but your posts indicate that you have identified your open side as a clear problem, so start there.
BTW, the Master Handbook of Acoustics showed louvred doors as a rough way to test/tune diffusion. You mentioned one such product. Idea is very simple and simple to test. Buy a properly sized louvred door for your hall opening at a refundable hardware emporium. Play with it by moving the louvres from completely closed to various openings and opening directions. See what that sounds like. Return the door when you've figured out how the physics of sound actually sound in your real world situation.
I think you really only have 2 alternatives for open doorways, especially on side walls. You can install a full door, something that basically is as solid and reflective as the wall itself, or you can leave the open archway and start playing with absorption on the opposite wall.I've got the same problem in my room - two 57" wide open archways in the right side wall plus that wall is the bend in the L-shape. One of the arches is right opposite the right speaker. At least there is a wall for most of the side - in my previous room the right side was almost completely open into the dining area except for around a 3' stub of a wall at the front of the room. I have never managed to successfully balance the sound by putting anything in the opening in either room. On the other hand, absorption or diffusion opposite on the left wall has tended to be very successful for me, with a bit of other room treatment around the room as well.
Play with putting something in the opening, but also play with putting absorption on the opposite wall and see which you prefer. It can be a pain, but you can end up balancing the sound while leaving the opening untouched.
David Aiken
Thanks for the ideas!Also, how did you find the multi-pipe roomlenses behind the listening position? Where else did you put them?
The multi-pipe units work extremely well behind my listening position. The room is L-shaped with the toe of the L behind me, extending from the left wall to a bit past the line of my right shoulder. The front part of the room extends a further 7' or so to the right.I haven't tried the multi-pipe units anywhere else in the room. The front part of the room is well treated with absorption and I found the normal pipe arrrays really didn't add anything there so I actually put them in the garage for about a year. Then I brought them out when I started to think about what I could do in the rear part of the room and played with various arrangements of four 3 pipe units there, before starting to experiment with these arrays. Basically they grew out of what I had been doing in that area.
David Aiken
This post is made possible by the generous support of people like you and our sponsors:
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2025, Audio Asylum, all rights reserved ]