[stevenkelby]

Hi All,

Can I QRD diffuser be made out of OC 703? Can I bandsaw it up and glue it into a diffuser?

Or must I use EPS foam for QRDs and put OC703 behind them?

This is for my front wall, behind GR Research Super Vs, (open baffle, 3ft out into room) and will be the only treatment in the room.

First reflections are taken care of with couches.

I have 400mm (16") of depth to use, 1000mm (39") width each side (with a 600mm gap in the middle) and 1070mm height to use up.

I plan to make a full width cabinet with gear shelves in the middle 600mm and use the 1000mm either side for treatments behind the speakers. Why not get absorption and diffusion out of the space behind the speakers if I can

QRDude says a QRD with design freq. of 350 - 400 Hz will fit in that space and uses a perfect amount of the local OC703 equivalent (Bradford Ultratel), just under 1 pack of 3 sheets of 50mm thick (1200 x 2400).

Looks don't matter as I will spray the whole thing black and cover the panels with black speaker cloth.

Thanks for any advice!

Steve.

[Ethan Winer]

Diffusers need to be made from material that reflects the frequencies you intend to diffuse. Most are made of wood, though some use hard plastic.

--Ethan

[stevenkelby]

Thanks for the reply Ethan, much appreciated!

Can I make the diffuser from styrofoam (EPS foam) then stick 4" - 6" of OC703 to the rear of it, then sit the unit a few inches away from the wall?

Would the OC 703 do any good like that?

I want to use EPS as it's light and cheap though I could use pine I guess.

Maybe I need to make normal diffusers and stick the OC 703 somewhere else in the room but I'd love to incorporate it into the front unit somehow.

[PDR]

Hi Steve.

When I made mine I used EPS, I then covered the foam with a coat of stucco primus.
Its a thin mortar made especially to adhere to EPS, up here in Canada a lot of buildings use
this as a base and then apply acrylic stucco over the primus.....been doing this for many
years as a building contractor.
After the mortar dried I painted it and applied a pre-finished board to the top and bottom.

To adhere the foam pieces together and to the backer board (Masonite) I simply used
spray foam from a can, the trick is to rub the pieces together so the spray foam no longer expands
and acts only as an adhesive.....another construction trick....

Even with the primus my almost 8' long by 4' high QRD only weighs less than 40 lbs.

Perry

[stevenkelby]

Thanks Perry, I get it now So the diffuser needs a hard surface, I think I will do exactly what you did with EPS and a hard mortar/stucco. Will have to find room for the bass traps elsewhere!

Thanks for the PMs too. Did you spray or brush the mortar?

[PDR]

I thinned the mortar down and applied it with a brush.
Once it had partially set up I took a 3M sanding sponge
and smoothed it out and sharpened the corners.
Little messy for a living room project, but my wife didnt object.

She was out of town at the time...........

[Big Red Machine]

You can also use the polystyrene from building supply which is slightly less vulnerable to cracking and breakage due to handling with its higher density than the EPS.