Hi Terry,
Well, yes I have the same question as yourself, if I go with all N11, can't you just flip some upside down, following the Barker code?
Another question: what is gained (beyond a bit of closer mic-ing, and loss of LF), between 2x N11 and 1x N23?
To your thoughts:
Quote:
Originally Posted by terry j  In any case, the point of ease of manufacture is not to be sneezed at. That is the reason why *I* prefer applying the barker code by rotation of the same qrd by 180 degrees. Saves making two different types (normal and inverse). If you are going to do a Mr Ford, do it completely. |
My question is related -- why not just flip some of the N11s (using the +2 constant) as Collo described above, and here:
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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 [LF] frequency of 811hz
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But since Barker fails for 8, 9, 10, 12 periods of the same type, one must have either 5, 7 or 11 periods (etc.) of the same type, it seems. What does 'flipping really do, for an N11? Can you in fact use 8 periods of the same N-prime effectively?
Barker Code Chart
1[-1]
2[-1 1]
3[-1 -1 1]
4[-1 -1 1 -1]
5[-1 -1 -1 1 -1]
7[-1 -1 -1 1 1 -1 1]
11[-1 -1 -1 1 1 1 -1 1 1 -1 1]
13[-1 -1 -1 -1 -1 1 1 -1 -1 1 -1 1 -1]
If 'flipping' worked, then why not substitute 4 N23 for the 8 N11, as this fits in Barker, and just do this: -1 -1 1 -1? If only it were this easy ... 'Flipping' has been mentioned before in other threads 
So there is another way to get close to my 380cm length with 4 arrays (qudude to the rescue):
N23 N23 N19[+3] N23 = 377cm
N19 with a constant of +3 yields: 940LF - 4300HF
(effective: 470Hz - 8600HF)
- - - - - -
Collo, what I meant by "if one is able to arrange zero wells across the frames you are actually getting 100% QRD across the entire array"
Just that in multiple arrays which each have a frame put around all the wells of a particular N-period, the two adjoining QRD arrays are then split apart by the doubled frame width. Wouldn't this part -- the 'flat zero space' between, act like a flat wall between the periods? But if you span the two frame members with a zero well that's part of a QRD array itself (like I had suggested with the N23), acoustically there is no frame -- that is, no extra space between the wells of adjoining arrays -- I think.