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First DIY 13-well QRD diffuser completed...finally!

tomlinmgt

tomlinmgt

Lunatic Member
And boy, was it every bit the bitch they say it is. I definitely have some better construction methods/techniques in mind for the second one. As a matter of fact, I'm not even going to detail the build yet as I see much room for improvement in that regard.

All that having been said, here it is...my third go at diffusion (but my first go at proper diffusion). My first two panel designs were rather "shotgun" in approach but did provide a positive contribution to room/speaker interaction. This go 'round I decided to get serious and sat down with QRdude and started running lots of different calculations. I settled on an N13 design (13-well) that covers all the critical mid range (and then some) and offers true diffusion at five target frequencies (only the more expensive commercial panels accomplish this).

This design has a usable frequency range from 415 Hz to 4526 Hz (scattering from 415-831 Hz) and true diffusion at 831, 1662, 2493, 3324, and 4155 Hz. It can also be used as close as four feet to the listening position so it's a great panel for large or small listening spaces. 1D well-type QRD diffusers will also offer some LF absorption by virtue of the design and the Dow foam insulation board I used is absorptive from around 350 Hz down.

I plan on building three for the front wall and three for the rear wall and perhaps a few for each side wall. If I stay on schedule I should have them completed, oh, I don't know...before the rapture, maybe. I'll share my recipe if I can get the construction method sufficiently refined it becomes doable for your typical DIY-er in less than the seven hours this one took. Oh wait, make that eight hours since I still have to paint this one. :sigh:

- Michael
 

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Ooh... I want to make a couple of these myself. Potentially put them behind my Maggie's and deepen the soundstage. My room shape congests the soundstage towards the middle between the speakers and it drives me nuts sometimes.

Please do update us with a streamlined DIY manual if and when you feel like sharing it.
 
Diffusers are going to be my next build but have a lot to learn on the
technical design end of things.

Doing a similar style as yours is there a pattern that can be a somewhat
catch all without using specific frequencies and room dimensions?
 
totem said:
Diffusers are going to be my next build but have a lot to learn on the
technical design end of things.

Doing a similar style as yours is there a pattern that can be a somewhat
catch all without using specific frequencies and room dimensions?
Click to expand...

A true QRD diffuser uses (somewhat) complex mathematic equations to arrive at the frequencies at which diffusion occurs with the variables being well width, depth, and number of wells. Ideally you want diffusion occurring across as much of the spectral region that constitutes mid range content as you can get. The deeper the wells the lower in bandwidth it will be diffuse. The narrower the wells the higher in bandwidth it will be diffuse (down to 1"). And the greater the number of wells the more diffuse the panel becomes.

This one would be much easier to build.....

http://gikacoustics.com/product/gik-acoustics-qrd-diffusor/

....but it doesn't cover as wide a spectrum as the design I chose and the lack of fins, which create the "wells", will make it much less effective if the sound waves are coming at it from an angle. Basically it would need to be directly in front of or, in the case of dipoles, behind the speaker to be effective. Add fins to it and it becomes much more versatile wrt placement and more diffuse.

Google QRDude and play around with it. It's fun and pretty simple.

- Michael
 
Alright...stay tuned, folks. I've located new, easily obtainable materials to make this build easier, quicker, more aesthetically appealing, more professional, and it's lookin' like a little cheaper (under $75 for a unit that exceeds the performance of units in excess of $300). I'm so excited I had to post. :yippy:

Now if I can just find the damn time to put em together. :sigh:

- Michael
 
So, like ... what's a qrd, and why must it be defused? :D

Been looking into doing something similar for the top corner of an arch that faces the main speakers and is directly behind the listening position. I figure to do unequal width and height on the elements and then just contact cement some cloth over the top to pretty it up. The thing would be around one by six feet long and be mounted diagonal to the ceiling/arch intersection. Haven't really decided on vertical or horizontal orientation on the slats or the angle of the diffuser. Just something that would direct any bounce and echo away from the ears mostly. Best bet would probably be to add pivots to the mount so I can adjust it to taste. Maybe add some wedges every foot to pitch the "vanes" for want of a better word, out more to the sides to catch any reflections off the side walls.

Absolutely no science to my approach until now, but maybe a bit of reading on this qrd thingie may be in order.
 
If you're going to mount on a diagonal you might want to consider a 2D design....or what's typically referred to as a "skyline" diffuser.

http://images.search.yahoo.com/imag...vv&sigi=11n9i4sk7&.crumb=aFZEYxtONNH&fr=moz35

And all the acoustics muckity-mucks say :nono: to cloth over diffusers....even the acoustically transparent stuff. Which I'm totally ok with as covering them is just more work. And if you build them out of wood they look cool. Like, Architectural Digest cool.
 
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tomlinmgt
Alright...stay tuned, folks. I've located new, easily obtainable materials to make this build easier, quicker, more aesthetically appealing, more professional
Click to expand...


As I have not started mine yet it seems that may be a good thing.

Do we get an incite into your next iteration or am I going to have to wait till
a completed version is ready for viewing?
 
It will be 11 or 13-well, around 2'x4', 1"x8" pine frame, 3/16" ply for back and fins, 1"x2" rough cedar for well faces. All lumber easily obtained at Home Depot and if you have a power miter saw and get the cats at HD to cut the fins from the 3/16 ply you'll be working with all square edges so everything will come together tight, tidy, and nice. I've assembled it in my head several times today. I'll build one this weekend come hell or high water.

- Michael
 
Well, dammit, the forces that be conspired against me and exploited every opportunity to completely muck up my weekend schedule so, no, I didn't get that diffuser built. Bare with me....it's comin'.
 
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