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In Reply to: RE: Diffusison posted by pictureguy on September 07, 2016 at 21:24:41
A polynomial Diffuser (see picture) is limited in frequency buy its depth and actually profides a lot of attenuation as well (no necessarily good - but it could be) the evective frequency the the 1/4 wave defined by the differences in the depth of the difusor components eg. 3" difference works at 1kHz and up. A wedge or tube diffusor is also determined by its size. By angling a dipole speaker the extension down to lower frequencies can be enhanced. I use a 45 degree toe in on my planars that essentially fire into the rooms corners (one corner has an equipment rack and the other a software rack).
24" x 24" is too small consider twice or three times that. 24 x 72 is a typical side wall diffusor I use for non-dipoles baffled speakers. 36" by 72" for a front wall diffusor behind each speaker.
"The hardest thing of all is to find a black cat in a dark room, especially if there is no cat" - Confucius
Follow Ups:
Polynomial is a new term to me. Though I KNOW it is a math term.
What I want to build LOOKS similar (but not exactly) and is called a 2D QRD.
I would think that as you DIFFUSE the back wave of the panel, you will also reduce its amplitude as you spread the SAME energy out over TIME.
I'm ok with that.
Too much is never enough
more attenuation occurs with w QRD panel because of phase cancellation. one portion of the reflected wave becomes 90 or 180 degrees out of phase with reflecttion from other portions of a signal.
The Drawback of one of these "stepped" QRD like panels when used directly behind a planar dipole that is parallel to the diffuser is that specific integer frequencies get attenuated or theoretically reinforced while other frequencies do not.
In most installations the diffuser is not going to be back wave.
The cheapest way to make non QRD style geometric reflective diffusers to make are plywood or particle board boxes. Vinyl lovers use the crates or boxes behind the speaker or angled against the wall and stacked on each other to the desired height. You can also build some of the cubes as a boxes with a damped tuned port to be a home made "tube Trap" helmholz attenuator.
"The hardest thing of all is to find a black cat in a dark room, especially if there is no cat" - Confucius
Fortunately, the panel and the diffuser are rarely parallel. In my case, they'd be offset by about 11 or 12 degrees. Panels are vertical.
The OTHER kind of diffuser I've seen is the 1D QRD, which is a big box with steps in calculated depths and all the same width. These can be pretty much as LONG (tall) as you wish. I don't have the facilities to construct these, since I'd need a good table saw and MUCH more construction space than currently available.
Calculators I've seen are 'seeded' with a Prime Number which may be key in avoiding 'cogging' frequencies.
How is a 2D QRD behind a panel any WORSE than the bare wall?
Too much is never enough
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