As someone who had a graduate-level (post-bachelor's) course in electromagnetic fields, I'll take a stab at some aspects of "phasing" issues.
As long as the drivers in the L1's are connected similarly (i.e.: driven "in phase"), the only source of "phasing" from the L1's would be from differences in the signal path between the input to the two amps and the connections at the speakers (making the assumption that the drivers themselves are as identical as technology allows them to be ... and let's also assume the two amps are identical and the wiring from the "common point" into each of the two L1 amps are the same type and length)
To get a bit technical (as opposed to auditory): a rough "speed of signal in a wire" is 1 micro-second/foot. So, even if the physical layout designer kept each wire in the L1 columns to the minimum length required to reach each driver (which keeps the wiring simplest but is the wrong thing to do for phasing)
, then the worst-case difference between the top and bottom drivers is ~6 micro-seconds. Now, I think that my ears only start to hear a difference when "clicks" (or delays) are more than ~3 milli-seconds apart -- so the difference between the top & bottom L1's may be 1/500 of an audible effect? Of course, if care was taken to make the wire lengths the same going from amp-to-Lowest-driver and amp-to-Highest-driver, then any resulting "phase" differences within the column would be entirely differences in drivers and the two amps involved.
However, another way to look at this is to look at the wavelength (in air
) of the frequencies of interest. That is: at what frequencies will differences in apparent "delays" between the drivers cause a significant phase difference? Roughly speaking, the lowest C on a piano has a wavelength of ~32 ft (8' open organ pipe = 1/4 wavelength on lowest note). So, 5 octaves higher (soprano high C), the wavelength is ~32/(2*2*2*2*2) = 1 ft; at 180Hz, wavelength in air is ~6 ft (B1 cross-over frequency), while 15KHz =~1 inch. (If you want to get precise, check out this link
.) So, if there are differences in wire length along the length of the L1 it *can* cause phase differences of the upper frequencies.
Remember, however, that the speed of an electrical signal in a wire behaves very differently than the speed of sound in air ... a wire signal is much faster (>1000 times faster), and rather frequency independent
... at audio frequencies, anyway.
Note that mechanical systems (e.g.: speakers) can join into resonance. That is, as long as the phase difference is small enough, there is enough "slop" in the mechanics of speakers that they will "self-align" -- begin to resonant -- at a common frequency. So, if care is taken in the signal wiring length, and the use of 'identical' speakers, then a column should exhibit little "phasing" effects.
What are some other implications?
(1) If you use a long cable between the PS/1 (base unit) and the first B1, use the shortest cable you can between a pair of B1's. Even though that "daisy-chain" cabling results in a slight delay between the two B1's, when you physically stack the boxes there is enough "slop" in the physical dyanmics that they will act a single system (the 3db gain often referred to in this forum). (By the way, a resonant floor [e.g. a wooden stage] can also provide that mechanical coupling if the B1's are placed side-by-side. Stacking them just removes the issue of worrying about the flooring characteristics.)
Phasing between the B1's and the L1's is not an issue if the crossover is sharp enough (and will only be an issue at the crossover range)
2) If you use a separate bass amp with a crossover point that overlaps the L1's low end, you can get some "interesting" phase effects rather easily. With or without B1's attached to the PS/1 base can complicate that effect even more!
3) You can begin to appreciate why it is a great idea that any particular "sound source" is only feed through only one L1 column; that is, why one should avoid the "dual mono" operation of two (or more) L1's. No matter how close or far you separate the two L1 columns, there will always be some audio freqencies that will be "out of phase" (as well as geometric phasing effects for all frequencies, which is more complicated than can be explained without a diagram).
This all may not be relevant to what Cliff-at-Bose was interested in discussing; I'm guessing he really wanted discussion if anyone could hear
any phasiness.(corrective editing)