Diffusor (QRD?) - Slightly different design

[gazpianoman]

Hi Guys,
I've designed the following based on a diffusor I saw at Thomann... I'd appreciate your feedback. It had to be really simple to make as it was supposed to be a student project. Will this still be a useful acoustic panel?

Thanks

Gareth

[gazpianoman]

Thought I'd add an indication of the space too... your thoughts on this greatly appreciated too... I've designed it all!

[Jason Jones]

Originally Posted by gazpianoman

Hi Guys,
I've designed the following based on a diffusor I saw at Thomann... I'd appreciate your feedback. It had to be really simple to make as it was supposed to be a student project. Will this still be a useful acoustic panel?

Thanks

Gareth

Gareth,

That is a pretty nice looking panel. But.....as a diffuser...not so good. The cyliniders will be good diffusers at high frequencies, but the repetition will cause problems and they won't be effective at mid or lower frequencies.

You could take that same box and add planks...for lack of a better word...rectangular bars instead of the cylinders. If you arranged a group of 2" (~5cm) bars in a quadratic residue sequence that would work well. It would be heavier and more work, but doable (is that a word?).

Another option would be to use a 1/8" thick piece of plywood and make a poly diffuser. That would also work and be a reasonable amount of work.

Jason Jones

[andrebrito]

Not that good since it would not really act as a grating diffuser. High frequencies are diffracted by the semi cylinders but for the rest of the frequencies it just acts as a plain wall.

[gazpianoman]

Hi,
Thanks for your replies so far...

Jason, are you suggesting something like the attached? That's the Thomann one which seems to fit your description better. I don't think I really understand the finer details of diffusion, I can't get my head around why the sound has to be channelled into parrallel slots in order to get a reduction in lower frequencies... But hey, that's why you guys are in business!

Regarding your second suggetion, I did kind of see my design as a Poly diffusor as it had the bent ply backing to radiate the sound on contact, but with added bars to further disrupt reflection... have I missed the point with designing a poly?

Would you suggest something more like the second attachment would be a better diffusor? I was thinking of maybe using a sheet of fibreglass or something as the backboard to provide a little absorbtion as well? If so does the depth of the 'channells' matter? How do I calculate these? Is incorporating some absorbtion defeating the point of a diffusor? Appreciate your feedback!

Thanks

[jayfrigo]

Originally Posted by gazpianoman

Regarding your second suggetion, I did kind of see my design as a Poly diffusor as it had the bent ply backing to radiate the sound on contact, but with added bars to further disrupt reflection... have I missed the point with designing a poly?

It's such a slight bend that it won't scatter much. The most common poly is the semi-cylindrical, which means that you would use the entire half of a cylinder. Yours was essentially a tiny slice off the top of a huge cylinder. The very small cylinders in front would only be effective at very high frequencies. Also, there is no time-domain component, if that's important to you. Overall, it would do something, but not much.

[gazpianoman]

Ok, so the concensus that the first idea is a nice bit of furniture, but a bit useless!

How about the second one?

Thanks

[johndykstra]

Originally Posted by jayfrigo

It's such a slight bend that it won't scatter much. The most common poly is the semi-cylindrical, which means that you would use the entire half of a cylinder. Yours was essentially a tiny slice off the top of a huge cylinder. The very small cylinders in front would only be effective at very high frequencies. Also, there is no time-domain component, if that's important to you. Overall, it would do something, but not much.

Jay, if you would, could you check out this thread:

http://www.gearslutz.com/board/bass-...-included.html

regarding the purposed room treatments for my room. I wonder if your comment regarding polys here would apply to my space, as I do plan on making quite a few of them.

Also, in regards to time-domain component, is that to say that a poly will scatter the sound, where as a qrd, has a time-varied "bounce back" and thus will have more of a reverberation effect? It being obviously difficult to describe a sound, if you could try to clarify in simple verbage the difference in the two principles.

Thanks alot

John