Wasting my time with homemade diffusers?

Posted: Wed Aug 15, 2007 2:47 am

Hi Eric,

I'm glad you saw this message. BTW are we the only ones NOT on holydays ? Surprised

eric_desart wrote:

1) Since such bend panels also have edge diffraction/diffusion I have the feeling he made the panel longer to limit this edge effect on the top ends.

don't the other devices also have edge diffraction/diffusion ?

eric_desart wrote:

Note that the way this is measured... does not really relate to the surface area of the sample (bit simplified)...

Agreed

eric_desart wrote:

3) Whether this is best or not I leave open. What I do know is that I have a lot of experience with polys, always with succes (also using the edge diffraction by hanging them free), and that as far as you go back in history labs are executed with polys, including the own reverberation room of RPG (has additional reasons) itself.

That's most interesting. Funny enough I have in my personal notes done a while back a plan for a free standing poly, using only a piece of plywood mineral wood and strings.

eric_desart wrote:

4) I find this a wrong interpretation of these graphs.

I noticed the level difference in the text and in the graphs... I should have mentioned it, sorry

eric_desart wrote:

Hence whether that's better or not, is not so clear to me. It shows some coloration... But clear is this is a time delay effect for that Schroeder diffuser, which means that another sound is returned/reflected than what you sent to the diffuser. It should be interesting to see a spectral analysis of this graph as well.

I agree fully. Down the road it might be a matter of personal taste and needs, related to individual situations.

eric_desart wrote:

5) I don't do explicit statements about this.

I should have said "Should we understand from this document curved panel are more scattering than diffusive devices ?"

Posted: Wed Aug 15, 2007 3:15 pm

msikio wrote:

eric_desart wrote:

1) Since such bend panels also have edge diffraction/diffusion I have the feeling he made the panel longer to limit this edge effect on the top ends.

don't the other devices also have edge diffraction/diffusion ?

The edge effect of the flat panel can be almost ignored. The Schroeder type must have, but I can't judge the relative importance versus the Schroeder principle at work. The bend panel at the top edges (where you have this hollow bend) diverts rather strong from the main principle. And as you can notice is also used to measure scattering in 2 directions.
But what I do here is only thinking out loud/guessing without knowing the real motives of the author.

msikio wrote:

eric_desart wrote:

5) I don't do explicit statements about this.

I should have said "Should we understand from this document curved panel are more scattering than diffusive devices ?"

Note that this document and study is made to compare methods to quantify scattering, not to study differences in diffusers. Therefore the diffusers in themselves aren't even exactly described or investigated.
They just used 3 very different types, to see how they behaved in function of the rating methods under investigation.
Hence be careful to make explicit conclusions.
I don't like this kind of slogan like things.

What you can see is that bend panels show a smooth diffraction behavior (which confirms what I knew about them), that Schroeder like types show a more lobbed behavior (the 1/4th wave-length resonance influence), which I always had some question marks about (and which is badly documented).
For me the question which scatters more and exactly how much isn't that important.
At least this doc shows that bend panels are good and not some cheap, non-learned, alternative for guys with too limited budget, interest or energy to invest in serious acoustic treatments.

Using bend (or not) panels as diffusers/reflectors is making use of geometric acoustics and is easier controlable.

Eric

This topic sponsored by: