Thanks everyone, this is really helpful!
Sorry to make a mistake, my dividers are 2.5mm (not 25mm!) plywood (I read that 2.5mm would be acoustically transparent or near-to).
These two equations are the same, below?
"The N11 panel can achieve a more economical depth by using
well depth = (well number squared + 2) mod 11" (is the same as the first equation)?
how did you arrive at:
2 3 6 0 7 5 5 7 0 6 3
(maximum depth 7/11)
?
I am surprised to learn that the well width might need to be
wider than 3cm, in relation to the 13.5cm depth?
I think you're suggesting that both N7 + N11 have the same LF cutoff. And to build the N7 shallower (max. well depth = 121mm) to match the LF of the N11 (max well depth = 135mm), yes?
Quote:
Originally Posted by collo  Some numbers might help....
The standard N11 equation..
well depth = (well number squared + 2) mod 11
gives well ratios of:
0 1 4 9 5 3 3 5 9 4 1
(maximum depth 9/11)
The N11 panel can achieve a more economical depth by using
well depth = (well number squared + 2) mod 11
giving well ratios of:
2 3 6 0 7 5 5 7 0 6 3
(maximum depth 7/11)
For your maximum depth of 135mm, these translate to:
38mm 57mm 115mm 0mm 134mm 96mm 96mm 134mm 0mm 115mm 57mm
Giving a design frequency of 811hz Switching to your N7 panel...
Design frequency of 811hz gives a maximum well depth of 121mm
Depths: 0mm 30mm 121mm 60mm 60mm 121mm 30mm
And I agree with Terry - we will require pictures....  |
Sorry, no pictures yet as nothing is built, though I can diagram the room... When I do construction I'll be taking pictures, for sure.
Jason you wrote:
Quote:
Also, the 7's have greater issues with the "flat plate" frequency issue (the design frequency * the number of wells...in your example 728hz *7 = ~ 5Khz) which will limit the high frequency effectiveness of the unit. The flat plate frequency is the frequency range around which your diffuser behaves like....well....a flat plate.  For an 11 diffuser the flat plate frequency is 1Khz*11 = ~ 11Khz.
|
With N7, it seems that my HF cut of 5.7kHz is 'close' to the flat plate Hz (5096Hz). If I raise my N-7 LF to 811Hz, my HF cutoff becomes 5677Hz, matching my well width of 3cm. I would prefer not to alter the 3cm well width, if possible. My plan is to cut 3cmW 1pcf construction foam (polystyrene? - the blue stuff, very hard to cut with a knife, very light, flexible) to the well depths, and face them with 2.5mm plywood. (I am not building much LF absorption into the unit, but the foam will eliminate well resonances.) It makes the build
MUCH easier.
I'm excited to go with the N-11/7/11/11/7 idea, and it looks like I should raise my 7-prime LF to 811Hz.
According to your ideas about the relationship of LF to HF cutoff, how could the RPG QRD-4311 possibly work, with a well width of 1.1" and max well depth of 16". I think then that LF=
404 - HF=6164 Hz. (404 x 4 = 1616Hz, but the unit cuts off at 6164Hz). Please explain why the depth is so great to the very narrow well?
Alton Everest says (pp. 311-12, 2001 ed.):
"The number of wells and [narrowness of] well widths affect the performance of the units. The QRD 4311 having the deepest well depths and the narrowest well widths (feasible from a manufacturing standpoint) gives the highest diffusion coefficient over the greatest frequency range. For comparison, two other units ... the QRD-1925 and QRD-734 are built with primes of 19 and 7 and well widths of 2.5 and 3.4 inches. The performance of these, while good, is somewhat inferior to the QRD model 4311.
So I'm a bit confused here, concerning the LF relationship to well width. My choices are either 3cm (1.18") or 5cm (2") well width, in terms of available materials/construction methods.
I'm making headway, thanks to your suggestions, but would like to clarify the well width/HF/flat plate issue...
Comments? I'm probably missing something.