DIY 11-well 1D QRD diffuser

tomlinmgt

Lunatic Member
This is my second attempt at a 1D QRD diffuser with my first attempt being a 13-well unit. That first design....

http://www.audiokarma.org/forums/showthread.php?t=517397

....was very labor intensive and challenging to build, so for the second one I went back to the drawing board and came up with something that is a bit more compact, is easier to construct, offers the same performance (maybe even a little better), is lighter in weight, and looks better.

For the second unit I chose an 11N (or "11-well") design that has an effective range from 382 to 4526 Hz. Here are the performance parameters...

Scatter frequency range: 382 to 765 Hz, 3825-4526

True diffusion frequencies: 765, 1530, 2295, 3060, 3825

Minimum distance to seating position: 4.5'

Like the 13-well unit that preceded this one, this particular design is similar to commercial units costing several hundreds of dollars. I was able to build this unit for less than $70.

All materials came from Home Depot. The frame is 1"x8" rough cedar, the well faces are 3/4"x2" rough cedar and the fins and back plate are 3/16" (5mm) Luan plywood. I used a combination of wood screws and Loctite trim and panel construction adhesive (water based and dries clear). The overall dimensions are 48" tall x 20" wide x 7 1/2" deep and it weighs 15-20 lbs. I used rough cedar for its light weight and for the optimal adhesive bond its rough surface would provide (one side is smooth and one side is rough so the exposed/outer surfaces are smooth). I also happen to like cedar....a lot. I had the well fins cut at Home Depot and I highly recommend you do the same.

You can see the basic construction methodology in the pictures I attached. Basically I started by cutting the back plate, one side frame and both top and bottom frame pieces first. The side frame was glued and screwed into place. The top and bottom frame pieces were only screwed into place as they will need to be removed and reinstalled toward the end of the build. Once the partially completed frame was constructed I started installing the wells. Using pieces cut from the same 3/4"x2" cedar the well faces are constructed of, I made "pedestals" on which the well face sits. The height of the pedestal, less the thickness of the well face (3/4"), dictates well height (or depth, depending on how you look at it). In the second picture you can see that I have installed the pedestals for the third well. The fourth picture shows the third well with the well face installed, and the fourth shows the fin installed to complete the third well. The fourth picture shows initial construction of the fourth well with the pedestals in place. The fifth picture shows all wells now installed (note spacers in the empty wells) with only the remaining side plate left to install.

Up to this point everything has been glued in place and has started to set (it was in the upper 90's so it set up fairly quickly). However, I did not glue the ends of the well faces, fins or pedestals where they touch the top and bottom frame pieces. Allowing the top and bottom frame pieces to be removed enabled me to trim them as I wasn't exactly sure how much the glue would change the calculated width of the unit. Turns out not much as I only missed the calculated width by about half an inch. Even still, I'm glad I allowed for the removal of these pieces as they would've been a pain to trim if they had been glued to the other parts of the assembly.

The final step was to trim the top and bottom frame pieces, cut the right side frame piece, and glue/screw them into place. Be aware the wells need to be air tight, so before the last three frame pieces go on all surfaces that make contact with the frame will need to have glue applied to them.

If you want to construct your own QRD diffuser but want to try something a little less labor intesive I'd suggest you try a 7-well unit. It won't diffuse as much of the frequency spectrum as this 11-well unit, but it still offers effective diffusion and is usually what one finds when in the market for entry-level commercial units. There are several well configurations that can be constructed, but I strongly encourage you to familiarize yourself with the QRDude software to simplify the design process. The software can be found here...

http://www.subwoofer-builder.com/qrdude.htm

Ultimately I'll build three more of these so I can have a 40" wide array of two panels (butted one up against the other with one inverted) on the front wall behind each dipole speaker and the 13-well unit centered on the front wall between the speakers. I'll be updating this thread with installation, implementation, and performance details....so stay tuned.

- Michael
 

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Thanks for posting this. I'm going to have my Maggie 2.5's up, in a room that's a little small for them soon and I think some diffusors like this will help. The previous diffusion device (bubble wrap) did in fact help in this room with my MMG's but an actual QRD diffusion device should be even better.
 
Thanks for posting this. I'm going to have my Maggie 2.5's up, in a room that's a little small for them soon and I think some diffusors like this will help. The previous diffusion device (bubble wrap) did in fact help in this room with my MMG's but an actual QRD diffusion device should be even better.

Yep, you'll need it more than ever, Ricky. The best you could've hoped for from the bubble wrap was a little scattering of HF. All my prior attempts at diffusion have been that...just scattering. Deliberate, purposeful diffusion is actually a very exact science requiring mathematically calculated devices. I'm learning a lot over on gearslutz where those guys take this stuff very seriously. E. Winer is a regular over there as well as Glenn Kuras (GIK Acoustics), recording studio designers and several authors of books on acoustics. Of course, I mostly just listen and ask dumb questions. :)

I'm taking a leap of faith that all the time I'm investing in building a bunch of QRD's will pay off. As I understand it the more you implement the more effective it will become. Unlike hanging a few absorption panels at first reflection which usually has an immediately noticeable result, it takes quite a bit more diffusion devices to really hear a significant difference. I'm hoping I'll get there. Hey, if nothing else they look cool as hell.
 
Maggies make you go further!

Hey, don't discount that scattering of HF :D It brought the imaging off the wall behind the speakers (wood paneled) forward to the plane of the speakers themselves. Of course Maggies make you want more.
Hmm, might be just the ticket with speakers with rear firing tweeters. In a room with no SAF concerns, that is :yes:
 
Hey, don't discount that scattering of HF :D It brought the imaging off the wall behind the speakers (wood paneled) forward to the plane of the speakers themselves. Of course Maggies make you want more.
Hmm, might be just the ticket with speakers with rear firing tweeters. In a room with no SAF concerns, that is :yes:

I agree. I built what I thought were diffusion devises but they really only turned out to be scatter-ers (?). But one thing is for sure, sound stage presentation did improve, if only slightly.
 
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OK, what's the difference?

I asked this question recently on an acoustics forum and according to the experts here's what I got back...

"scattering = energy spatially dispersed in the non-specular direction. that is, energy NOT reflected in the "angle of incidence = angle of reflection" direction.

diffusion = design frequency (and multiple there-of) w/ equal energy diffraction lobes generated.
"



"Diffusion = Equal distribution (in directionality terms)
Scattering = Unequal distribution (in directionality terms)
Specular = directional beaming
"



"Another attribute that may separate "scattering" from "diffusion" is that "diffusion" affects the time domain, not just the amplitude/directional domain."

Bottom line....scattering is easier to achieve, but diffusion is better (when done properly). :D
 
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Or what.

Definitely "or what".

Oh hell, Josh. I just started building the second of four last night and hope to knock em all out this weekend since I won't have the kids. I'm not gonna blow sunshine up anybody's ass, these things are a bitch and take a long time to build. If I build a pair for the back wall they'll definitely be 7-well units. But man, I don't know how many more of these I want to tackle. I'd like to get my front and rear walls treated ASAP and ASAP might be weeks, months even, if I have to build another half dozen. Those GIK Gridfusors are starting to look pretty attractive. And those Saturn diffusers are getting lots of positive feedback....I'm considering them, as well. :scratch2:

http://gikacoustics.com/product/gik-acoustics-gridfusor/

http://www.soundcontrolroom.com/shop/saturn-polycylindrical-diffusor

What do ya think of those Saturns, Josh? Interesting, huh?

- Michael
 
I haven't started the 11,s yet, but at say $70 apiece for the Saturns 24"x24" the outlay
does add up.
 
I wonder how hard it would be to make some similar diffusion panels out of paper mache or fiberglass.
 
Alright, two more done over the last several days. That's three 11-well units and one 13-well unit. Once more 11-well and that completes the diffusion devices for the front wall. I have build time down to about 4.5 hours and have started using more screws than I did in the original design....which helps keep everything square and moving along. I'll see if I can get it down to 4 for the fourth one. This just got fun as hell. :yes:

And I'll be damn if the plastic trash can lids I saw at Lowe's didn't look a hell of a lot like those Saturn diffusers. :scratch2:

Wonder how much math there is in the curvature of the Saturn unit creating a tailored diffusion pattern?
 
And I'll be damn if the plastic trash can lids I saw at Lowe's didn't look a hell of a lot like those Saturn diffusers.
Wonder how much math there is in the curvature of the Saturn unit creating a tailored diffusion pattern?

That's a question worth lifting the trash can lid over.
 
Bigger?

This is my second attempt at a 1D QRD diffuser with my first attempt being a 13-well unit. The overall dimensions are 48" tall x 20" wide x 7 1/2" deep and it weighs 15-20 lbs. - Michael

Michael, do you know or can you point me to the answer of "what-if" the "diffuser" is made 72" tall instead of 48"? I'd really like to make a set of these for my Maggies (MG-2.5's) and it seems like they'd be more effective if they were at least as tall as the speakers.
:scratch2:
 
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