Low profile mini polys ?

Here's a draft plan for mini polys to be used in conjunction with absorptive panels on the ceiling of a low ceiling basement : The aim is to treat flutter echo between floor and ceiling and add a little bit of diffusion. The dimensions are in inches. The average angle is 8° I'm thinking of using 1/8" dense fiber board as the panel and damp it on the inside face with a fine layer of rubber. Also I'm thinking of sealing the cavity with acoustic sealant. Any thoughts ? Thanks in advance, Michel

Just understand that it's not going to reach down very far and you're not very far away from it but it will help some purely to eliminate slap. I'd recommend using some absorbtion in the area where the 2 poly's meet. Bryan

I doubt it will even eliminate slap echo. Not a good idea IMHO.

John & Brian : thanks a lot for the replies. This is for a low ceiling (6.8') basement, so space is limited. I don't want to add more absorption as the RT in the room is already good. The floor is made of laminated wood. I redesigned the device, but in the light of your answers I believe it's still not right :shock: Anyway here's the new design, using round pieces of wood : F.A. Everest in his book says "Any angle between 5 an 10 degrees is usually sufficient for control of flutter echo". I designed the panel with a 8° angle. I assume a significant portion of the bare areas of the ceiling must be treated to make an audible improvement on flutter echo. Do I miss something ? Thanks

I think that that close to the ceiling 8 degrees will be insufficient to stop flutter echos. I've had flutter echos off 6 degrees at 10' so 8 @ 6'8" wouldn't be enough IMO.

John Sayers wrote:

I think that that close to the ceiling 8 degrees will be insufficient to stop flutter echos. I've had flutter echos off 6 degrees at 10' so 8 @ 6'8" wouldn't be enough IMO.

You mean the minimum angle is ceiling height dependent ? Suppose we increase the angle to 13° : Is that would be better ? Thanks a lot

A flutter echo is some kind of mode behavior (wave, not ray) with a pulse too short to develop as a traditional standing wave. John refers (I assume) to angled ceilings where one has a certain angle between large surfaces. Without having really tested this (hence with some reservation), my belly tells me when you make your first or second design ca 2 by 2 ft (independent units) and you hang them spread somewhat, they will prevent flutter. The (additional) difference in impedance between the diffuser and surrounding ceiling will cause diffraction and disturb the conditions needed for flutter. But as said, not tested. But I think other things play a part here than just the angle of this small parts. You also can't see this as just a series of convex diffusers, since the concave parts work as a focusing mirror (and for large waves even as a pseudo flat surface). I think just splitting this stuff up, hanging them with some space in-between one another, and possibly playing a bit with the suspension height versus the ceiling can possibly do the trick.

Hello Eric, I think you're 100% right even if you're not sure ;) I had thought of the advantage of diffraction created by the frames. I'm going to make a few 2'x 2' units, I think it makes a lot of sense especially as they can be orientated at 90° angle , to create a more even dispersion. More news in a few weeks. Thanks a lot, Michel

i would agree with Eric on the individual units - the separation between each 2x2 unit should help with diffraction at certain frequencies. that said, John's point about the angle is that the short lengths of the angled surfaces don't necessarily translate into a reflective surface large enough to stop the echos as the sound hitting it will only reflect for a small percentage and the rest will for all intents and purposes act as a flat surface for the bulk of incident angles. you could build a set of poly diffusers which are shallow enough to meet your needs and add trapping to your space. using peg board can give some Helmholtz effects as well.

Thanks Glenn, I will try a few prototype and I will post the result here. All the best, Michel

The 2' x 2' units on the ceiling, combined with 2' x 4' units on the walls worked very well. Flutter is 99% gone. I also like the sound of those little units. Thanks a lot to everybody. Here's a picture, sorry for the bad lighting

Eric_Desart wrote:

........my belly tells me when you make your first or second design ca 2 by 2 ft (independent units) and you hang them spread somewhat, they will prevent flutter.

:twisted: My belly knows more than I do .....

msikio wrote:

I think you're 100% right even if you're not sure :wink:

Eric_Desart wrote:

:twisted: My belly knows more than I do .....

And I knew about that ;) Thanks a lot Eric

Hey msikio, those units LOOK very cool. Got pix on the construction of those panels?

Thanks a lot :) No pictures of the construction, sorry !