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.