Thanks.

-uW

Phase issues in line arrays become more apparent at higher frequencies, because of the distances involved. If multiple woofers are driven by the same signal, there will be no phase interaction between woofers at the lowest frequencies. The frequency where interaction becomes significant is determined by the distance between drivers, and when you get to a point where wavelength becomes close to the distances between them, the speakers will begin to beam and lobes will form.

For frequencies above the point where the system begins to form lobes, sound becomes directional, specifically, it is strongest at positions where the distances between the listener and drivers are equal or multiples of a wavelength. Other positions will cancel out, where where the distances between the listener and drivers are equal or multiples of a half-wavelength, so directionality can be controlled by the positions and phase of the drivers. This is the basis for arrays, and why they are generally built as vertical arrays rather than horizontal arrays - to keep distances equal along the horizontal plane.

So basically, if you're just wanting to build a system with two or four woofers, you can do this pretty easily provided you are willing to crossover low. That avoids the issue of interference, and the drivers act in unison, as a single source. But if you're wanting to run the speakers at higher frequency, then you'll want to put them in a straight vertical line, so that the distance between listeners and each driver is the same.

But be carefull! If you're gonna use a combination of series/parallel coupling of the drivers in order to maintain a reasonable impedance (the only other alternative being using seperate amps for each driver, may for two in parallel), the condition for the reflex box working proberly might well be altered to an extent where it doesn't do that anymore - coupling bass-drivers in series is tricky business, particulary in a reflex enclosure.

I imagine adding a third woofer would create a situation where the outer two interfere with each other around 400Hz. I've considered the 3 woofer vertical "array" as "do-able" for a while now...using 2226J's the nominal z would only be 5.33 ohms, and parallax issues won't be too bad, as the relative distances from the woofer to listener might not vary much.

Add a fourth woofer to the array, now we're still looking at an easy 4 ohm load, with 4 jbl2226J's in parallel. But UNLESS you position the woofers along an arc like Pro Arrays, parallax issues will become more prominent. Maybe not an issue for "home hi-fi". And stuffing a horn in there somewhere for the HF, along the vertical axis, is going to force an even larger gap between at least two of the woofers in the array.

Intuitively, I'm thinking the array format is designed for SPECIFIC pro sound applications, and will create more problems than it will solve if implemented poorly. I'm not clear what characteristics it has that would be so desireable for home use that acceptance of the self-interference and parallax issues would be considered worthwhile. Sam

ps, when the "benchmark" is the performance of a pair of 4 Pi Pro's, you have to get pretty fancy to do any better:) and NOTHING ELSE that fits in such a small footprint is available, period.

• http://www.jblpro.com/pub/cinema/5674.pdf

Bill

• Linus array white paper