The amount to add inside the modulus varies with the panel order.
I can't give you a formula, but here are the optimums for a few
N7 already at best depth saving
N11 use +2
N13 use +4
N17 use +4
N19 use +3
N23 already at best depth saving
If you're looking at an N17 / N11 combo, you might be best to go for different frequencies for the panels. This will break up the periodicity and let you utilise the full 135mm depth in each case
Your N17 stats are right, but you can do better...
Adding +4 inside the modulus gives you a design frequency of 972hz for your 135mm depth.
Here's the breakdown: (since you were side-shifting the N11's you may as well do the N17 so it will mate up)
Data for One Dimensional QRD (Quadratic Residue) Diffuser
Custom N17 panel: Shifted down 4 depth units and left 8 wells
Design frequency 972 hz
Number of wells: 17
Deepest well in mm 135
Fin width in mm: 2.5
Width of wells in mm: 50
Ratios 0 0 2 6 12 3 13 8 5 4 5 8 13 3 12 6 2
Well depths in mm 0 0 20 62 124 31 135 83 52 41 52 83 135 31 124 62 20
Phase shift in degrees 0 0 42 127 254 63 275 169 105 84 105 169 275 63 254 127 42
LF cutoff frequency 486 hz HF cutoff 3440 hz
Panel width 892.5 mm
Minimum distance to seating position 2124mm (3 times wavelength of LF cutoff frequency)
Your side-shifted N11's come in at:
Data for One Dimensional QRD (Quadratic Residue) Diffuser
Custom N11 panel: Shifted down 2 depth units and left 3 wells
Design frequency 811 hz
Number of wells: 11
Deepest well in mm 135
Fin width in mm: 2.5
Width of wells in mm: 40
Ratios 0 7 5 5 7 0 6 3 2 3 6
Well depths in mm 0 134 96 96 134 0 115 57 38 57 115
Phase shift in degrees 0 229 163 163 229 0 196 98 65 98 196
LF cutoff frequency 405 hz HF cutoff 4300 hz
Panel width 467.5 mm
Minimum distance to seating position 2544mm (3 times wavelength of LF cutoff frequency)
Since these are both shallower panels than normal, either the 40mm well width or the 50mm will be fine. (HF cutoff 4300hz vs 3440 ... I would go for the 40mm for the better bandwidth, but it depends on your needs as far as overall panel sizes goes)
The 424mm panel width referred to earlier is the minimum you need for a design frequency 811hz (one wavelength). The panels can be larger than this though.
The Realtraps dimensions you gave model fine. For the RPG QRD-4311 you would need to know the overall width and depth to model it.
As for adding absorption into the wells, I think that's a whole other area of expertise. The above figures are for the standard maths, assuming solid well bottoms.
phew!!!
