Here's a reply of mine to a question from another part of the forum:

Phasing on this system is perfect. I would invite discussion on this. (pull the pin, throw the grenade, wait...)

Whattaya say, theroetical psychoscientists? Let's play ball!! Who wants to serve?
Original Post
Ok, I'll take a stab, although I'm not a real physics guy. I think you may have been fishing for a discussion of the phasing problems with stacking 25 drivers next to each other in a straight line, and I'll say that if there are problems with this, I couldn't hear them when I went to hear the System at GC Cinci. It sounds like really high end PA gear, no holes or strange peaks that I could percieve.

My question about phasing would be between the sub and the array. My perception is that I hear a distinct separation between the two, even at some distance. Nearly every separate sub system I've heard has this quality and I wonder whether or not anybody else hears this?

If I'm not imagining it, could it be that 180hz is a bit more directional than we think, or that it's critical to line up the drivers as planar as possible? When I heard the system, the subs were about ahead of the line array by the length of the B1's plus some 6 inches. Could that distance create the schism I hear?
Well, I'm no theroetical psychoscientist, but I figure that in any one Personalized Amplification System(tm), all of the drivers are getting the same aggregate signal and they're all pushing/pulling in unison. Therefore, zero system-induced phase shift...

Now time-alignment (coherence?) could be another matter, but I figure that we'd have to get the B1 further than the supplied cable will allow for that to be significant...

Keep those grenades coming, folks. Cliff's asking for discussion here...

[Edited for clarity, I hope...]
Just a thought...

since the B1' are stacked beside, and not under, the L1's the 180Hz-and-under frequencies are mixing in with the upper frequencies as they are pushed out to the audience.

Since the B1's use larger drivers and push more air than the L1's, doesn't it seem that the B1's would defeat the drivers in the L1's that are at the same level on the stage?

I realize that, because the frequecies aren't the same, this wouldn't actually be a phase problem. But it does seem (to me, anyway) that the pure muscle of the B1's would win out, and make the lower L1 drivers kind of useless?

Jeffrey
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)
Amazing that this came back up after October 2003, when we introduced the products. I'll admit here that I was indeed fishing, especially for many of the urban psycho-science myths-of-physics surrounding sound, the sound business and sound equipment. Sort of priming the pump for a general discussion on politics or religion. Never happened; no one took the bait. Our forum readers and writers appear to be a pretty astute group.

Nice contribution Dan, thanks. I for one learned a few things.

Jeffrey: At crossover (about 180 Hz), the B1's and all the L1 drivers playing in unison are in phase and contribute essentially half the acoustical power each. The crossover in the power stand is a pretty steep one, 24dB/octave. So an octave above crossover, the B1's are 24dB down and below crossover the L1's are 24dB down. They get out of each other's way pretty quickly.
"urban psycho-science myths-of-physics surrounding sound"

My favorite of these is 'throw'.
As if.

Ok, so I kind of assumed that the thickness variance in the L1's speaker mounting washers would probably create more phasing problems than Dan's 1 microsecond wire delay. We've also ruled out sub placement due to a 6 foot wavelength at the crossover frequency. So, about my issue with the 'un-integrated' sub sound. Could this be created by directionality? I know 180hz is supposed to be pretty omnidirectional but...

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