DIY quadratic diffuser

Hey Bob, Happy New Year. I looked and looked and looked for this stuff before the net got so big. Just found this today. YEAAAAAAAAAAAAAAA!!!! Do you have Everests book? Bought it in 94. Thats how long I've been looking for the math. And how to interprete it. :rolleyes:
Check my next thread I'm posting tonight, you'll see what I'm working on. Its a lesson in confusion:D
fitz
 
Rick - thanks for that link - Through his links page I was able to find a site I've been trying to find. It's al the BBC research papers, check out this stuff, these guys started the whole acoustics trip and they back it all up with research and testing. The good old BBC. ;)

Just down load the PDF files.

http://www.bbc.co.uk/rd/pubs/reports/index.html

Happy reading :):)

cheers
john
 
i still cannot visualize what this thing looks like. does it have to be hexagon shaped? does it have to be hung from the ceiling? are there any angles involved or just different depths? sorry, i know this was probably stated in the article, but my reading comprehension is absolutely horrible.
 
No, No, and Only if you build an Octagonal one - otherwise, it's just boards parallel to each other, with stops dadoed in at varying depths according to the prime sequence mentioned on the web page.

They work just fine as a modular thing, you can build 2 foot by 6 foot boxes with the divisions running the long way - then, you could put 3 of them vertical on the back wall, with a fourth one laid horizontal across the tops of the other three, for dispersion in two axes...

Just don't build and sell them, unless you have a good lawyer - I'm not sure that RPG doesn't still hold the patent (bastards)... Steve
 
OK, here's a crazy thought....

Reading the BBC paper (thanks for one more thing there, John!), I see they made their prototypes from square PVC pipe. I don't know how available square pipe is, but I wonder about this:

Take a bunch of normal (CHEAP!!!) PVC sprinkler pipe. Depending on what frequency range you are looking for, 1/2", 3/4" (would be about the size of the BBC pipe, or 1". Round pipe would fill about 78% of what square pipe fills, with a funny little gap between pipes.

Cut the pipes to the different lengths used for the diffuser.
***** QUESTION: How to best cut hundreds of pipes??? *****

Fill the end of the pipe. I'm thinking plaster or spackle type of compound. Make a tray about 1/2" deep, put the pipe down in and give it a twist, pull it out and wipe the outside off. My goal is a filled pipe, as opposed to a cap which would be wider than the pipe. If the in-pipe material is too soft (i.e. if it would absorb high frequencies too much), then after the material dries, stick the whole end in varathane.

Using hot glue, glue the mess of pipes together. Lay a bead or two on each pipe, and stick it in position.

When dry, paint the assembly if desired, and hang it on the wall or ceiling using velcro strips.

I'm thinking I can make a diffusion surface that will work just about as good as the $300. panels for less than $10.

The theoretical performance might not be as good, but I'm thinking the real-world performance might be very very good for very very cheap.

Am I insane?

-lee-
 
Yes you are probably insane, but it never stopped me !
There is lots of square plastic and fiberglass tubing out there.
We use it in our circuit board shop alot for railings and odd house
fab stuff. In fact I saw a huge pile of 2" glass tube in our dumpster yesterday and was going to grab it, but couldn't
come up with what I would build, da ! Anyway I like your idea,
If I can come up with a source or manufacturer of the square
stuff I will gladly let you Know, The epoxy/fiber stuff is easy to work and holds up to almost anything.

Good luck, Bob by the way, I never admitt I'm insane,or did I ?
 
Just don't build and sell them, unless you have a good lawyer - I'm not sure that RPG doesn't still hold the patent (bastards)... Steve
Click to expand...

Steve - in those BBC papers there is a whole rave on quadratic diffusers written in 1990 by one of the BBC researchers. I doubt that RPG can stop you building or selling a diffuser.

cheers
John
 
laptoppop said:
OK, here's a crazy thought....

Reading the BBC paper (thanks for one more thing there, John!), I see they made their prototypes from square PVC pipe. I don't know how available square pipe is, but I wonder about this:

Take a bunch of normal (CHEAP!!!) PVC sprinkler pipe. Depending on what frequency range you are looking for, 1/2", 3/4" (would be about the size of the BBC pipe, or 1". Round pipe would fill about 78% of what square pipe fills, with a funny little gap between pipes.

Cut the pipes to the different lengths used for the diffuser.
***** QUESTION: How to best cut hundreds of pipes??? *****

Am I insane?

-lee-
Click to expand...

lee,

They make a PVC cutter, that looks like a simple pair or shears, or wire cutters. Its very easy to use and quick.

QUESTION 1: Wouldn't a round object be just as efficient if diffusion? Think about this: Sound travels out from a source in all direction in a wave. A huge sphere that travels out from the source, the distant is the radius from the sound object.
(I'm dragging this from my physics class years and years ago)
SIN(circle) = sine wave, Does anyone remeber this, I think this is correct.

QUESTION 2: Would the PVC be placed in a square grid pattern or a honeycomb patern. or even alternating for a more irregular pattern.

Just some thoughts that came to mind
Larry
 
I've used one type of the clippers for PVC pipe when installing a sprinkler system. It worked fine, but by the end of the day, my hands were quite tired. I liked the nice sharp cut at the end. I'm hoping to find something that works as well, but is either motorized, or gives me more leverage. I figure I'll be cutting about 10 times more than the typical sprinkler system.

1) Round versus Square -- I don't know, but I suspect that the round tubes might give more soft even diffusion along the sides than square tubes. One thing that bugs me is that I don't know how the little holes at the corners would affect things.

2) Pattern - I'm thinking that the tubes would be in a square (rectangle?) pattern. I'm still working on the right lengths for the various tubes. The BBC paper has a nice full pattern described, but it uses a smaller pattern -- I think I'd like a deeper pattern.

-lee-
 
I checked on the square tube,
and there is a lot out there,
but the price is high. the pvc is real steep.
I guess I should be in the dumpster more !
I still like the Idea of trying the round stuff !

For cutting plastic alot of contractors use
a chop saw, but it cuts hot and you have to go fast.
I cut alot of plastic and epoxy, and think for home
use a carbide blade for plastic in a power miter
might be the ticket.
just remember heat is your enemy and the trick
is not to fine a tooth, low rpm and a relatively
high infeed. You will end up playing cut quality
or smoothness agianst melting.

If you really get into this, and want to cut a bunch,
Let me Know. I could certainly be of some help !

I personnally have too many things to do on my own
to want to sell these, but drilling and cutting plastic
and composites is my job, and I would love to see
it go well for you.

By the way sprinkler tube is pretty thin, I am
heading to the hardware store and will be looking
at all the tubing. I may have a better idea.
the above thought may be more aplicable to
thicker wall.

good luck, Bob
 
Holy you know what, I was just examining the RPG site on DEFRACTALS. WOW! This is PERFECT for the aluminum extrusion idea. I knew I saw it somewhere. GOTTA GO DRAW!!! see ya later tonight
fitz.


BTW.....gatorhaus, thankyou so much for including me in your thankyou list. I certainly don't consider myself in their league in any way shape or form. But knightfly should. Compared to these gentleman and others, I'm the court jester, just stirrin stuff up to get some more answers free!!!LOL:rolleyes: Anyway, I 'preciate it. Even if its misplaced:D OK, wheres my jesters hat?

Opps, while I'm here.......(stir,stir) just kiddin....
later.
 
lee,

Wouldn't a hexagonal (honeycomb) pattern be extremely efficient, and more natural with a minimal space between the round pipes, not trying to change your mind or anything just throwing it out there again, I might try a round pipe hex pattern for a diffuser.

Now about weight condsiderations? Filling with plaster how much will this weigh compared to how large it will be. Will it hold on a wall with velcro strips?

What other type of material could be used that would be dense with a lighter weight (or is that a contradiction).

Rick,

Your welcome, and I didn't mean to not include anyone. Your names appeared because ya'll have been the most willing and helpful to me. And that I really do appreciate

Thanks,
Larry
 
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