DIY broadband absorbers questions...

[_Morph_]

Hi.

I am currently building some home-made (and rather cheap) broadband absorbers, and I would like to ask you a couple of things.

The absorbers consist of three layers of rock wool (30kg/m3; 1,57in thick), hence 4,7in thick; the rock wool is held in place by one of those blue styrofoam panels, and the 6in arrangement is packed in a home-made stitched bag made out of ordinary polyester fabric (slight resistance to breathing).
Rock wool side will facing front; styrofoam side to the back, slightly away from the wall.

1) For what i've read, the styrofoam shouldn't provide nothing but a slight acoustic absorption/reflection. It serves solely the purpose of holding the rock wool in place. Are there any side-effects to this arrangement?

2) The absorbers will be wrapped with the aforementioned fabric. But I wonder if the fabric will keep the rock wool particles inside, or will those pesky tiny buggers escape bit by bit?

Thanks!

[Ethan Winer]

Originally Posted by _Morph_

the rock wool is held in place by one of those blue styrofoam panels

Without seeing what you have it's impossible to comment. How thick is the styrofoam? How large? Where is it - on the edges only, covering the 2x4 foot surface? Etc.

I wonder if the fabric will keep the rock wool particles inside

I'm sure that will be fine.

--Ethan

[_Morph_]

Thanks for the help, Ethan!

I thought I had been descriptive enough, but I obviously forgot to mention that. The styrofoam is covering the whole back of the panels (47in x 24in). It is 1,1 inch thick.

[Ethan Winer]

In that case I suggest you not use the styrofoam because it can interfere with the absorption.

--Ethan

[_Morph_]

Ok, Ethan.

I guess it'll be harder to keep the rock wool in place, but I'll manage.

Thanks very much!

[Glenn Kuras]

Originally Posted by _Morph_

Ok, Ethan.

I guess it'll be harder to keep the rock wool in place, but I'll manage.

Thanks very much!

I would think the fabric would hold it in place.


Glenn

[_Morph_]

Hi, Glenn.

I'm afraid it doesn't. I mean, it does keep the rock wool panels inside, but they bend easily. That's why I thought of introducing a panel of styrofoam in the back, to keep it straight.

[jwl]

Morph, that's one of the challenges of rockwool, it's trickier to get nice neat edges. Maybe try a layer of cotton batting between the rockwool and the cloth, with something firmer (like thin cardboard) on the corners to give them more shape?

[_Morph_]

Thin cardboard along the sides. Good call!
I wish I had thought of it earlier.

But does the styrofoam make such a big difference, or just a slight "eq" change?

Thanks!

[Glenn Kuras]

Originally Posted by _Morph_

Thin cardboard along the sides. Good call!
I wish I had thought of it earlier.

But does the styrofoam make such a big difference, or just a slight "eq" change?

Thanks!

You could use the styrofoam on the sides but just not the back.


Glenn

[Old Goat]

I was thinking of using two pieces of carpet tack-strip across the back of the Rockboard teeth up to give it something to hang from. One at the top and one halfway down should be enough, I would think.

[_Morph_]

Ok, guys. Thanks for the help!

I'm almost done and can't wait to try them out.

[_Morph_]

Hello, guys.

I would like to thank once again for all your advice.

The broadband absorbers work quite nicely and lately have been used quite a lot, as multi-purpose panels:

a) Bass traps (in the corners of a large room already fitted with broadband absorbers and quadratic diffusers).
b) First reflection absorbers (on a low ceiling and on a wooden floor)
c) Quasi-portable vocal booth (in a small room, they worked like a charm with a SM7)

They were really cheap and are doing wonders to my tracking sessions!

Thanks once again!