Constructing 2D QRD Diffusors

Brandon Drury —  February 18, 2012 — Leave a comment

Here’s a pic of my back wall at the moment.  Ignore the Roxul wrapped in fabric at the top.  That’s just temporary until I can build the next set of diffusors.


I made a multitude of mistakes when constructing my diffusors so hopefully this section will help you not repeat my faults.  I’m NOT a construction dude.  I’m a wanna be guy.  I’m like those wanna be recorders still using the stock soundcard in their laptop.  On most days I’m clueless but every once in a while I pull something interesting out of my ass.

QRD Dude told me the exact number of linear feet of 2x2s (actually 1.5” x 1.5”….don’t get me started on that rant) so I bought a few extra.  For what I had in mind I needed 53 2x2x8s which cost me about $100, give or take.

Wood Dry Out

The wood at Lowes wasn’t exactly A-grade wood (which is okay with me) and some of it was pretty soaked.  One piece may weigh double what another piece weighed.  The first step was to let it dry.
Wood dry out


Then the sanding began.  I initially used a 180 weight sandpaper, but that was way too fine for what I’m up to.  This isn’t neurosurgery woodworking.  It’s more blunt-force woodworking and I found a 60 weight to be much better for smoothing out all the rough stuff and the final results are fine.  (Actually, as we’ll get to, other factors got in the way of these things looking as good as I wanted them to.)  If a person wanted to go full-blown death on this sanding business and make each piece of wood perfect, I’d guess you’d finish this project about when my grandkids die or when India loses it’s status as the world superpower.
Note:  Notice my unique lawn mowing pattern to confuse the cops.  This is my first year of not getting a formal warning for not taking care of my yard. 




Jasmine, the bitch from up the street, decided to inspect my work up close while attempting a breaking an entering to my home.  One benefit of being 31 is you start to find dogs trashing your work humorous.  When I was 25 I would have pulled out my .45 ACP and removed the hostile.


Here’s my setup for applying the polyurethane.  I’d do one side of about a dozen boards, come back 45 minutes later, rotate them 90 degrees, and repeat.  I wouldn’t listen to me on this one as I had all sorts of runs.  My technique improved by the end where I was more careful to distribute the polyurethane evenly on the first swipe.

I tried out some new “hippie” paint thinner.  It was a buck cheaper and preached all the green environmental crap.  When I opened it, it looked like watered-down milk.  I wasn’t pleased, but the stuff ended up being pretty good.  The milky stuff disappeared when I do my polyurethane work.  I did find some good ol’ destroy-the-Earth mineral spirits that I used for final clean up just to make sure the brush was totally clean, but overall I’m pleased with this hippie paint thinner.

Paint Thinner

Big Problem: Circular Saw Support System

I had just read in a woodworking book about creating a guide support thingy for a circular saw to make it possible to cut very straight lines.  I thought this was awesome.  I made one and it worked well for some other things I was up to.  In this particular case, the 2×4 was too tall so I made a quick decision to shorten it and turn it around so that the motor of the ciruclar saw didn’t hit the guide.

Circular Saw

The one thing I didn’t think about was the angle in which the cut would be from one axis.  It didn’t occur to me that the super-short nature of this guide wouldn’t give much support on the other axis.  This is tough to explain via text so I’ll let the picture do 1,000 words.

The end result, which I underestimated the severity of at the time, was it looked like my 2×2 pegs had been through a hurricane. They were bent or sloped.  This meant assembly of the first diffusor took FOREVVVVVVVVVVVVVVVVER because the blocks could only be orientated one way.

You can see this clearly here.  This gap was caused by the larger 8 15/16” 2x2s with the bad angle mentioned above.  I really thought that the ability of the circular saw to cut 12 pegs at a time would be the most efficient.  Back to the drawing board.

Big Problem:  Polyurethane And Stain Before Cutting

I figured it would be more efficient to stain and polyurethane 8′ long 2x2s than try to stain and polyurethane 3” long 2x2s  That’s common sense.  What I didn’t factor was the splinter factor from sawing.


This immediately made me realize that I had made a mistake by doing the finish work first.  A part of me thinks that some kind of spray-paint solution of a color may not be perfect (and may be tough to get right in deep in the wells) but it has to be a better solution than this.  The best approach, as many have done around the web, is no finish at all.  Natural wood looks pretty cool and would save you a TON of time and headaches.

I thought I was doing something totally wrong that was causing these wretched splinters.  I did some quick research and found out that all saws are going to cause splinters on a crosscut.  It’s just an issue of where and how much.  Going slow is a huge help in reducing them.  The angle you hit the wood with the saw is another.  It turns out that I was hitting the wood at a terrible angle with the circular saw, which was cranked to it’s 2.5” max to make it through the guide and the 2x2s.  Not good.  This bit me in the ass later on.

Miter Saw

Miter Saw

I ended up going with the miter saw.  The miter saw always cuts straight at no angle (unless I want it to).  This totally solved the angle issue and ultimately made the assembly stage of the next two diffusors exponentially faster.  Don’t let the picture confuse you.  I was only able to cut 4 boards simultaneously with the miter saw, which did increase cutting time quite a bit compared to the 12 simultaneous boards I was getting with the circular saw.

Here’s a good example of what the best and worst cuts of the miter saw looked like.  The left is the top cut in the ideal position and the right is the bottom cut in the least ideal position.  The bottom of the left piece doesn’t look much better, however.  In the end I just rubbed off the splinters with my hand.  Ironically, I went through close to 450 pieces of wood and none of the splinters stuck to me.  On the first batch I used sand paper, but I wasn’t any more impressed with the results.

I want to point out that these saws are NOISY.  That’s kind of a given.  I always wear ear plugs with this stuff.  I saw something somewhere that 90% of your hearing loss is caused by the loudest 10%.  Just knocking the edge off the crazy loud stuff can be a huge deal.

My hearing is easy to protect.  I have to say that I started to feel guilty for making hundreds of cuts.  My neighbors were extremely patient and never complained, but I felt like an asshole by the end of the marathon of cutting.  If you are in the kind of neighborhood where running a saw for hours at a time is frowned upon, you may want to consider other options.  I get the feeling that there is some woodshop somewhere that can push 3 buttons and in 5 minutes 600 pieces of perfectly cut wood pop out.  Maybe not.



Panzer decided to sleep exactly where he’d get covered in dust from the miter saw.  He’s not the sharpest dog in the drawer!

When I told the ol’ lady that I wanted a lot of pussy, this wasn’t what I had in mind.

Note:  Weak attempt at humor over.  ;)


My 2D QRD diffusor called for 12 different peg sizes that started at 3/4” and progressed up to 8 15/16” .  I kept them organized by placing them in plastic Walmart bags.  I made sure to toss a sheet of paper with their length number (1-12).  This came in handy quite a bit as it’s easy to mistake the different sizes when assembling.  Best of all, it made little “compartments” on the couch that made it easy to grab the size I needed.  I considered buying little tubs for this, but the Walmart solution was totally adequate.
Grid Size

Here’s the 19.5” by 19.5” foundation.  I used 5mm thick plywood.  It served the purpose just fine.  This grid was entirely necessary to ensure that the pieces went in correctly.  I would have been totally screwed without it, although for some reason I really hated drawing those lines.  Not sure why.


Assembly Size

Here’s the first day of assembly using the pegs from the circular saw.  It’s easy to see how none of them line up right and the general worksmanship is somewhere between panty waste and dog shit.

One day two of assembly, using the miter saw cuts, productivity was infinitely better and the worksmanship is better.  Not good, but better.  I decided to live with the rubbed off splinters.  Time was running out.  You can see the MaxData function on the laptop from QRDude, which made it easy to keep track of where I was in the assembly process.

I found that by assembling two indentical diffusors at the same time I was able to save a ton of time.  If you take a look, you’ll notice that each half row (left to right in this pic) is symmetrical.  So every time I needed a size of peg, I simply grabbed four from the bag, one for the left and one for the right of each diffusor.
Wood Glue
Yes, perverts, I’m SURE that is wood glue.  On day #1 I glued each piece individually.  I kind of had to.  I also glued each side of each peg to the other pegs.  I had read previously that the additional glue connecting the pegs wasn’t necessary, but they didn’t qualify it any further.  My 12 piece (the longest piece) is 8 15/16”.   On day #2 I decided not to glue any of the pieces together.  I wanted to see if it was necessary to use any glue other than sticking the pegs to the foundation.

When I had to move the diffusor from day #1, when I picked it up it felt like I had picked up a cinder block in terms of structural integrity.  It felt like one piece with not a hint of flex.  Solid is a good word for it.  When I had to move the difffusors from day #2, there was some flex.  It was quite acceptable, but it wasn’t rock hard.  It felt strong enough, but my confidence level was lower on this one.  Who  knows what it will be like in a decade.  Wood glue is cheap.  So I don’t see any reason not to glue the tall pegs together, which is what I did for the last diffusor.

For what it’s worth, when a healthy amount of glue is added, these things are STRONG.  In fact, I had an overhang from one of the 3/4” pegs that I somehow goofed.  I noticed it about 3 hours after I had glued it.  I used both hands to attempt to shake the hell out of the damn thing to pull it off.  I gave up.  I suspect that with a flathead screwdriver I would have torn the wood foundation before the glue gave.  Since there is no significant  leverage working on the little pegs, I don’t see any need to reinforce them.

You’ll notice in this pic that I had all the pegs for the next go around ready.  I’d slap on glue for all the squares that needed it (some squares are empty) and quickly put the pieces I place.  This was a very efficient way of working.  You can’t screw around with this method, but I didn’t feel I had to rush.  While I didn’t officially time it, I want to say it took about an hour and 10 minutes to assemble both of these diffusors.  By far, prepping the pegs took dramatically more time.

If a person could find some lightweight material that could be ordered to be the correct size and finish, they could save a ton of time and headache.

Was It Worth It?

I DID NOT expect the work load to be THIS high.  It was a TON of work.  Each step makes via the pics makes it look like a wham bam thank you mam kind of operation.  Each one of those steps took quite a bit of time.  It was amazing how fast each hour flew by.  I started on Tuesday and put in long hours to get them finished by Saturday.

If you have more money than time, just buy some pro diffusors.  Gik and Realtraps make great stuff.  Tell Glenn or Ethan I sent you.

If you have free time and like building stuff, knock yourself out.  You will feel like someone beat the shit out of you.  At least I do.

It’s too early to speculate how they sound. Coming Soon.

End Result

Brandon Drury

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Brandon Drury quit counting at 1,200 recorded songs in his busy home recording studio. He is the creator of and is the author of the Killer Home Recording series.

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