Thanks, your information above makes the situation much more clear. This option:
"Optional N11 panel ........well depth = (well number squared + 2) mod 11"
is very cool! Thanks.
(By the way, can the above formula be successfully applied for higher N values as well? Does the '+2' constant change?)
Taking your comments into account, please consider these new options, below. I found out I can get 4cm depth EPS board, so:
1x N17
with 5cm wells + 2.5mm fins, fits almost perfectly (89.25cm) into 91cm (3') frame (
1199LF - 3442HF Hz).
2x N11's (squared + 2 option) + 2.5mm fins with
4cm wells (
811LF - 4318HF Hz). The 93.5cm length can incorporate the frame (1.75cm at each end) by beginning and ending with a zero well (same derivatives as you posted, just starting from a different point):
0 7 5 5 7 0 6 3 2 3 6 | 6 3 2 3 6 0 7 5 5 7 0
Well depth = 0mm 134mm 96mm 96mm 134mm 0mm 115mm 57mm 38mm 57mm 115mm "Giving a
design frequency of 811hz." I think 811Hz - 4318Hz looks quite good on paper for this depth diffusor. To continue, looking at 2x N11's with 4cm well width + .25cm fins = 467.5mm, which is over your 424mm Length to diffuse 811Hz. Did I miss a HF problem though, with the 4cm well width (you were recommending 6cm wells)? (If so, would there be a problem with the 2' x 4' x (5.75") N13 made by RealTraps, which likely has an approx. 4~4.5cm well width?)
Easier to build too. However, there's
the unavoidable issue of repetition. Will this symmetry (through 4 periods) create problematic acoustic issues? What are these issues? (Andre, in another thread, cautions against over-repetition of QRD periods.)
Extra notes.
Here is more DIY information on my proposed build. The costs are very low.
I looked at building absorption into the tall wells, but am leaning towards EPS foam (almost no absorption), because it is so much easier and cheaper to build. I think I will get enough bass reduction through the many traps placed above, below and in the corners of my room. If I am mistaken about this, please let me know ...
The problem I have is that the rigid rock wool I can get (in Japan) is costly, and does not provide a solid base for a well face, thus complicating the build. If I go this route, I can get and rip two 4cm faces from cheap 9mm D x 9cm W x 100cm L fir stripping boards -- ($0.55 each = $0.28 per face). But then, it's necessary to nailgun to height suports, nailgun face to fins, then glue/seal the wells - it's complicated.
Today I further investigated EPS "Blueboard" options. Can get 1cm, 2cm, 3cm, 4cm, 5cm depths (each comes as a 91cm x 183cm panel). I can go over 5cm to 6cm as you recommend (yes, doubling a 3cm piece). EPS is very light and stiff (not flexible as I said before tutt), easy to work with and lengths can be cut on a table saw, with the right blade.
I have two construction options for the well faces:
1) My first thought, for beauty as well as density, is to face the EPS with 2.5mm plywood (as I wrote before).
I am also considering though to,
2) use the EPS alone for facing, prime it with a water-based latex color, then shoot it with polyurethane lacquer, creating a harder, reflective surface. What do you think of this foam-face + latex + polyurethane idea? (I was thinking that EPS "blueboard" alone does not make a good reflective surface, due to its low density.)
FYI, even with wood faces, I've priced out a 93.5cm c 93.5cm (3' x 3') diffusor, including plywood faces of 2.5mm plywood, fins, EPS foam, plywood backing, 12mm x 13.75cm wood outer frame (ripped from a plywood panel), silicone sealer, glue, corner braces = $35. USD or less, total cost. If I go with foam-only faces + polyurethane, the price drops and labor drops a lot!
Notes.
I was thinking that my HF (therefore well widths) should remain the same for all N-primes (all diffusors on the wall). It makes the build much easier, too, with one standard. I could adjust width to 4cm or 5cm, but don't you think that if you raise the LF (less depth) and/or build wider wells you are reducing bandwidth to the point that the diffusor doesn't function so well?
And what about that RPG QRD-4311, which seems to go against the HF recommendations? This QRD seems rather awesome...
Quote:
Originally Posted by collo  Pack the N7's out from the wall with 14mm spacers and they will be flush with the N11's |
That will work for sure, and another option, if you choose to keep all backings flat against the wall, is to build up from in front of the backing: place a 10mm EPS sheet panel faced with a 4mm piece of plywood in front of the backing, the same size as the N7, then build the N7 on top of it. thumbsup
I hugely appreciate your input, suggestions, and help with the mathematics. It's an exciting project, I don't want to waste the time and effort due to my inadequate understanding and experience.