[Xenon]

Greetings Andreas,
I'm not sure what you're working on, it sounds interesting. Your Styrofoam 2D diffusor thread is one I've read several times. I hope to try something similar. You wrote:

Originally Posted by Lupo

PS: Congrats on the build! Looks very good.

Thanks!
And you wrote:

Originally Posted by Lupo

What I meant is that you want to be in the far field of the entire sequence. A 2 meter wide sequence needs longer listening distance than a shorter sequence.

Yes, what I don't quite understand is how in QRDUDE, the listening distances are arrived at differently. For instance (taking 135mm deepest well as a basis):

1) for N53, Panel width 2279mm: listening distance = 1656mm

2) but N23, Panel width 989mm: listening distance = 2076mm

So your comment and QRDUDE distance results are divergent, I think. Also you wrote in post #47: "The large number QRD's needs a longer distance to the listening position for all the waves in the diffuser to blend." But if you make a smaller well width (WW), a larger N-period is not necessarily longer than a smaller N QRD? But were you thinking of 'larger but maintaining a specific WW, for the sake of comparison'? Or just 'larger N = greater distance in all cases'? I wrote in post #50: "It seems intuitive that a shorter period length will 'cohere' or "blend" in less distance?" And showed these QRDUDE results:

QRDUDE Calc, listening minimum-distances:
N11(c2) = 254cm
N17(c4) = 212cm
N23(c0) = 208cm

Collo explained in post #51: "The recommended minimum distance to the seating position equals 3 times the wavelength of the LF cutoff frequency."

Do you disagree? Anyway, pragmatically, in a given (typical home/small room) application, the LF may change, but the max. well depth (MWD) is critical to the build. Of course we want the best LF we can get as well, but there must again, pragmatically, be a limit to how much room you want the unit to take up off the wall. In the above figures, following QRDUDE here are the LF numbers (MWD = 135mm) for each:

N11(c2) (473mm Length)= 254cm (list. dist.) = 811Hz LF
N17(c4) (731mm Length)= 212cm (list. dist.) = 972Hz LF
N23(c0) (989mm Length)= 208cm (list. dist.) = 994Hz LF

So the N11 with the least length has furthest listening distance (and lowest LF) and N23 with greatest length has the closest listening distance (and highest LF). On this point, between you and Collo, I'm confused, though I'm not confused about how QRDUDE is calculating listening distance.

It seems probable that actual period length must play a role in the time domain -- this issue has some buzz in loudspeaker design (temporal coherence --though here we are looking at incident reflection and phase).

Well I will pursue my earlier comment: following the Barker Code, in terms of difference, what makes a minus (-) to a plus (+)? Take a look at these four images from QRDUDE:
A

B

C

D


Consider this a thought-experiment, playing with the visual approach. For argument, all have the same MWD and WW. A&D have relative similarities (and what about A&B?), where A&C seem less visually similar. Of course D is N19 (and shorter in length than N23, and with a different LF), but my question is, can A&C, which are both N23, be considered as +1/-1, in that the periodic symmetry in either Barker sequence 4 or 5 (see below), we just need one 'different' array. We've discussed 'flipping' in various permutations. Tangentially applying this logic, A&C would appear to some extent to have an asymmetric relation to each other.

Barker sequences for 4 and 5 periods:
1) 4 periods: C as #3 in a set of 4 N23, with all others as A type [+1 +1 −1 +1];

2) 5 periods (as just above, but C as #4 in a set of 5 N23) +1 +1 +1 −1 +1.

At the distance at which all consecutive periods form a united incident diffusive wavefront (in a perfect world with only one wall), there may be issues. But how distant do you need to be from a multi-period QRD array which is at 500cm in length? And considering the Modffusor discussion above, might just moving wells as with A&C above, be sufficient? Advantages are a much more straightforward build, architectural niceties, possibly a benefit to maintaining the same level of diffusive resolution along the wall (in a small room), easier to dimension, less brainwork to build, time-saving -- did I miss anything (yes, RealTraps surrounds rooms with N13s on every wall surface--just to point out)?

I doubt there can be a definite answer without actual experiment, or some challenging math, but I'd be curious what the ripple tank would produce. And if you look here, at Finite Difference (and the links) it seems there may be a mathematical/theoretical method of determination (beyond my ability--and if this is even the correct application). Your thoughts?