The "Depot Diffusers"

A very easy to build, very inexpensive but good performing wideband sound diffuser design, effective from 400Hz to 8kHz or wider.  Optimized to use off-the-shelf dimensions of inexpensive firring strips (sold in large hardware centers in the USA, such as Home Depot, Menards, or Lowes).  Size is 34 inches wide, about 4.5 inches deep, and as tall as you want to build (easiest is 8 feet tall).  The Depot Diffuser is a 1D type diffuser, usually the best type to use in listening room to adjust ambience. 

These can be a nice one-day project and would almost certainly make more of a change to a system’s sound than changes to electronics or wiring, maybe even than changing speakers.
Best placement is usually 5 feet or more behind the listening chair, but reflection points or behind speakers are other options.

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Diffusers are a less often used, usually too-expensive type of room treatment. Absorbers are the more common type. Absorbers remove energy from sound waves that hit them, effectively smoothing responses and reducing specular reflections, and are usually the first choice. But after a point too much absorption starts to make the room seem dead or even downright uncomfortable to sit in. Diffusers break up specular reflections but don't absorb the energy. Instead, energy at different frequencies is scattered over a wide area and range of time delays. Diffusers don't kill the lively-ness of a room but can make it sound much richer and seemingly larger. Placed at reflection points or behind the listening chair, they make a dramatic and immediate effect, not one of those "I think I can hear it" kind of things.

These ultra-easy, wideband, inexpensive diffusers perform well from about 400Hz to 8kHz. They are 1D "step” type diffusers, optimized using the diffusion simulator “AFMG Reflex”. They simulate well, even compared to the usual QRD diffusers you might be familiar with. Credit for the assembly concept and instruction on optimizing step diffusers goes to Tim Perry at Arqen Sonic.
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This design size is ~34.5" wide, and up to 96" tall (or roughly 3'x8'). Making them 96" tall is probably the easiest height choice since it uses most of the lumber in as-bought dimensions and avoids the majority of wood cutting. The thickness of the assembly is about 4.5 inches. The wood, other than a few plywood base pieces, is inexpensive spruce/pine/fir "furring strips", commonly available in US. Needed tools can be as little as a hammer and nails and a pencil, if you can get your lumber store (or big box store) to do some simple cuts of the wood pieces for you. Assembly time is on the order of an hour or two for a basic diffuser, using a #18 1” brad gun (which made it really easy), longer if using only a hammer and nails.

The total cost of wood for one 8ft tall diffuser should be around $92 for one 8ft diffuser, with left over plywood. Two would cost about $152, three would be about $212.

WAF might be a factor choosing to install these, but I think if they were near floor-to-ceiling sized and painted to match the wall colors they could look pretty nice, or at least inoffensive. I like the way they look, even without any finish at all (though I'll probably sand and urethane them sometime).

The first step is to get the wood, enough to build the height you want to make. Try to pick mostly un-warped, decent looking pieces if you can. Here is what you'd need for one 8ft (96", minimum wood cutting), 34.5" wide diffuser. Alter as needed for other heights or quantities:

_____________ Wood List _________
*Qty 12 of 96" pieces of nominal "1x3" (~0.7"x2.4" actual) furring strips, about $2 each.
Part numbers are 164704 at Home Depot, 13PFUR.8 at Lowes, 1031528 at Menards.
*Qty 4 of 96" pieces of nominal "1x2" (~0.7"x1.5" actual) furring strips, about $1 each.
Part numbers are 160954 at Home Depot, 128218 at Lowes, 1031515 at Menards.
Plywood, from Home Depot 577138, or Lowes 12232 , or Menards 1251061; about $32 per 48”x96” sheet (you'd need two sheets to make one diffuser, or three for two diffusers). Home Depot cut mine to these sizes at no additional cost. You need:
*Qty 2 of 12.25"x96" plywood
*Qty 1 of 34.5"x96" plywood
To assemble, first lay the big piece of plywood down, ugly (unsanded) side facing up. Take one of the 1x3 pieces and set it on the plywood, aligned all the way to one (long) side. Then set one of the narrower pieces alongside the 1x3, for positioning. Move the 1x3 back and pencil mark the big piece at the four corners of the narrower ply (4 places) - also run the mark down the edge (thickness) of the big ply.
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Repeat for 4 more marks, starting this time with the 1x3 aligning piece on the other long side of the big ply.

Then, mark and draw 4 full lines the length of the large ply, spaced about half the thickness of the 1x2 wood pieces (~0.35”) away and inward from the previous marks – that is, toward the centers of where the narrow ply pieces had been positioned. The full lines indicate where to nail or drive screws to connect the 1x2 wood to the large plywood piece.
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Line up all the 1x2 pieces narrow side down and about 7 inches apart, then put the large ply piece on top of them, ugly side up. Pull one of the 1x2s over so that its end is along a short line you marked and so that the full line is about in its center. Align both ends to those lines.
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Then drive a 1” nail or brad through the ply into the 1x2, along the long line. Repeat at the other end, and about every 8 inches or so between. Repeat for all 4 boards, when done it should look like the photo above.

Move the large ply out of your way and lay down a narrow ply board “pretty side” up. Use one of the 1x3 boards to set spacing from one long edge of the ply, as before. Align another 1x3 next to it and nail that second one in place. Remove the spacing board. Align another 1x3 alongside the last one (toward the inside of the ply) and also nail it in place, then another one on top of that. Choose better looking 1x3 pieces to be the ones on top, where they will show, and use less nice ones as the covered-up pieces. Repeat with the other ply, remembering that these two ply pieces will be mirror images of each other.
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Now, lay down the large ply assembly, pretty side up and place the narrower ply pieces on top of it. Align the edges of the narrower assemblies as well as possible on top of the 1x2s of the large ply, with the 2-high stack of 1x3s toward the center, and nail the assemblies in place.

Lastly, nail a stack of three 1x3s on the narrow plywood pieces at the edges toward the center. And you’re done. That's it!
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