My home made diffuser

[4 the Max]

I am following the absolutely wonderful plans and photodiary by Jake Hartsfield:

DIY Acoustics III: I Did It - You Can Too by Jake Hartsfield (TuneCorner)

In studing his and other QRD builds on gearslutz, almost everyone is using luan (wood) for the fins and wells and pine whiteboard for the frame and well spacers, including DecWare's kit ($150 for single unit):
http://www.decware.com/p1324.htm


Like many of us on gearslutz, I just can't afford to purchase multiple $500 commercially-made QRD units.

I was thinking of using 3/16" foam-core for the fins;
and either 3/16" foam-core OR 1/8" matte-board (used for matting photos in framing) for the wells

Questions:
Is there some acoustically significant about
1. using luan (wood) vs. foam-core for fins and over OC 703 in the wells?
2. using foam-core vs. matte-board over the Owens-Corning 703 in the wells?

I was thinking that the matte-board over the wells might be better because it's thinner allowing more bass trapping by the OC703 beneath the well

The diffuser weighs and costs less than using luan:

Foam-core/Matte-board materials:
A.C. Moore, a local crafts store, sells
white 3/16" 20" x 30" foam-core for $2.69
colors 3/16" 20" x 30" foam-core for $5.99 (beige speckle, white speckle, gold, cyan, green, yellow, red, tan, gray, navy blue, orange)

3/16" 32" x 40" foam-core for $7.99
1/8" 32" x 40" matte-board for $7.99

In speaking to a cabinet-maker/carpenter who manages the local Home Depot contractor's desk, luan would require purchasing a 10" Ryobi table saw ($119), 10" 90 tooth blade ($40), and push shoe for safety ($20) besides all of the luan

The matte-board and foam-core can be cut with a utility knife and drywall T.

Aside from acoustics, wood QRDs look beautiful hanging on a wall. However, my main consideration is acoustics not aesthetics. However, if the wood build is acoustically better than foam-core/matte-board, I'll use luan despite the extra cost.

Thank you.

[mhch]

Originally Posted by dr jazz

Thanks for the advise but I'm not sure Gator board Exist here in France...
Perhaps it has another name?
If anybody has an idea...

May be use balsa and harden the surface with paint !! Utilises du balsa et rends la surface reflechissante avec de la peinture ... (yes I'm French too)

It's a good idea to fill the inner part of each slot (below a thin wood piece), using absorbing wool, as this also provides some extra bass trapping, specially if the diffuser is large.

[Jens Eklund]

Originally Posted by mhch

It's a good idea to fill the inner part of each slot (below a thin wood piece), using absorbing wool, as this also provides some extra bass trapping, specially if the diffuser is large.

http://www.gearslutz.com/board/5858024-post5.html

[Xenon]

Hi,

I built a couple of QRD walls for my live room, seen at the thread here:

QRD Prime + Period Question (Live Room)

There is nothing like QRDUDE free software to help you:
QRDude: Quadratic Residue Diffuser calculator

After some research by utilizing "blueboard" in the well gaps (40mm width wells, N23), there is some absorption between 150Hz-500Hz. Filling the wells involved a substantial amount of blueboard (you can calculate it based on the well width x height x depths). The blueboard was just the thing to keep the well widths uniform.

Keep in mind the absorption is not bass trapping. I think the amount of absorption has benefit, but the absorption is tangential to having a non-resonant acoustically absorbent material in the wells behind the front slats.

Look into corner bass trapping for instance (or Heimholtz corners, etc.) to achieve effective trapping (our live room has corner bass traps and 48Kg rigid fiberglass above/below the QRDs, and we built 15cm ceiling absorbers, with about a 5cm gap below the ceiling).

Our project studio live room can be seen here:

BigFish — Studio

Good luck. A lot of work but very cost-effective and totally worth it.

[DaggerToe]

YouTube - DonketasLoveOrgan.MOV

How would you connect all this together?

[localhost127]

Originally Posted by Jens Eklund

http://www.gearslutz.com/board/5858024-post5.html

Jens,
pardon me if i may have missed it in your previous explanations, but while styrofoam may not absorb as one would assume, is it still useful to be permanently used as a cavity filler for the diffuser wells?

or would you recommend simply using it as a guide, and then removing it and filling the well with fluffy insulation. (if the goal is only to minimize resonance within the wells, not to perform any additional overall absorption).

thank you,

[Xenon]

though you are asking Jens, I would like to say that as a diffuser is made of a dense material designed to reflect sound waves down to a certain Hz, and "fluffy" insulation at the volumes we are considering, absorbs HF/MF, its seems there is little absorptive benefit, as you are reflecting the wavelengths prior to the absorption, right?

The blueboard I mentioned has absorptive properties below the typical LF cutoff of all but really deep QRDs (check QRDUDE). So there is some benefit, though it is limited. Of course as mentioned you want to fill the void with something to prevent resonance. It needn't be fiberglass though.

Originally Posted by localhost127

Jens,
pardon me if i may have missed it in your previous explanations, but while styrofoam may not absorb as one would assume, is it still useful to be permanently used as a cavity filler for the diffuser wells?

or would you recommend simply using it as a guide, and then removing it and filling the well with fluffy insulation. (if the goal is only to minimize resonance within the wells, not to perform any additional overall absorption).

thank you,

[Jens Eklund]

Originally Posted by localhost127

Jens,
pardon me if i may have missed it in your previous explanations, but while styrofoam may not absorb as one would assume, is it still useful to be permanently used as a cavity filler for the diffuser wells?

or would you recommend simply using it as a guide, and then removing it and filling the well with fluffy insulation. (if the goal is only to minimize resonance within the wells, not to perform any additional overall absorption).

thank you,

EPS can be used in two ways: Either as the actual material of the diffuser if relatively dense (approx. > 25-30 kg/m³);

http://www.gearslutz.com/board/6521762-post2.html

or as a build guide when making them in wood DIY-style. Provided that the wood is glued to the EPS, it will not absorb noticeably but any diffuser will naturally absorb more or less due to other reasons.

[localhost127]

Originally Posted by Xenon

though you are asking Jens, I would like to say that as a diffuser is made of a dense material designed to reflect sound waves down to a certain Hz, and "fluffy" insulation at the volumes we are considering, absorbs HF/MF, its seems there is little absorptive benefit, as you are reflecting the wavelengths prior to the absorption, right?

no, the absorption within the wells is strictly to address resonation inside the wells --- not to be used as any part of an absorber in the classical sense.

much like the use of fluffy insulation between wall cavities.

[secret secret]

Thought I'd share a couple pics of my newly finished DIY skylines. I used 1x1s and stained them a bunch of different colors. I glued each row together first, then glued the rows together to make 2 12x12 panels, then glued the two panels together.

pic here: The Studio

[soundoff]

Secret Secret - What plans did you follow to build those skylines?

I'm considering building some 1X1's myself... just wondering how much background research you did. Is there a huge difference between skylines built with 2x2's vs 1x1's?

Also... out of curiosity... how far away from your primary position do you have that diffusor?

thanks,
soundoff

[chadking]

Just finished up my first skyline style diffusors. These are adjustable on the stand and easy to move. It was my first set, so I learned a lot. Next sets should have a bit better fit and finish.

Thanks everyone for the inspiration!

[localhost127]

Originally Posted by chadking

Just finished up my first skyline style diffusors. These are adjustable on the stand and easy to move. It was my first set, so I learned a lot. Next sets should have a bit better fit and finish.

Thanks everyone for the inspiration!

nice work! i like the gobo/stand idea.
i did the same thing (installed wheel casters on the bottom so it was mobile) ... but i also installed 4" OC703 on the backside.

this quickly lets you switch between a diffused surface and an absorptive surface, depending on what your needs are

something you may want to consider

[Cegor]

All of the diffusers look great so far. Any size(s) that's recommended for the fins?

[localhost127]

Originally Posted by Cegor

All of the diffusers look great so far. Any size(s) that's recommended for the fins?

1/8" luan ply