Why so few high end line arrays?


To me the intrinsic "wall of sound" of this design are compelling. I recently tried a very nice 3 way w/ stereo subs in my system after 2 years of line array-only listening and the lost impact and scale of eight midbasses/ribbons per side was profound. I was immediately aware of the music emerging from boxes, despite very nice imaging. And it's not that the arrays exaggerate the size of voices and instruments. Does the materials cost dissuade manufacturers? Is it the size? Seems like relatively unexplored territory in high end home audio.
jb0194
Like you, Jb, I have a pair of Selah Audio line arrays. They're very impressive and really envelope you in sound. But yes, they're big and dominate a room, invoking the WAF factor (it did in my case). And yes, the cost of 16 quality drivers per side ups the ante in terms of cost (though Selah's designs are a real bargain).
Also, the sound isn't for everybody. It's very dynamic and 'throws' the sound forward. Some like a mellower sound that draws you in. But the life-size soundstage and realistic dynamics make for a lively sound that's hard to resist, IMO.
They work great at concerts and for sports stadiums....definitely a mistake for home audio, IMHO.

You are getting serious comb filtering from listening close up to multiple drivers with the same bandwidth.
I discuss what I call "LSESL", or Line Source ESL design, in my most recent article at Dagogo.com. I'm referring in that term to the Kingsound King, a large planar (You can tell I'm just a BIT excited about this technology). Quad has used a similar concept in their speakers for years, and we all know how that's been received. To my ear, the multi-driver concept with the ESL technology is a fantastic combo. One can certainly achieve a tremendously satisfying result implementing multiple ESL drivers as opposed to cones.
09-04-09: Shadorne
You are getting serious comb filtering from listening close up to multiple drivers with the same bandwidth.
Not entirely true. Comb filtering is NOT an issue in nearfield listening if the center-to-center distance of the drivers used does not exceed a distance equal to the speed of sound (at ocean level) divided by the highest frequency handled by that particular line of drivers (bass, mid-bass, treble).

Dr. James R. Griffin, Ph.D, has a fairly definitive white paper on the subject titled "Design Guidelines for Practical Near Field Line Arrays"(.pdf) that discusses the subject in-depth. In the paper, he provides all the basic criterion for creating a successful line array:
Center-to-center Driver Separation (Circular drivers). We want our discrete driver array to approximate a continuous line source. This spacing is the separation between the centers of the adjacent drivers in the line and includes any mounting allowances and the flanges surrounding the drivers. In the limit the closest spacing would be dictated by the flange diameters of the drivers although some drivers have truncated flanges that would allow closer spacing. Two different solutions (Table I) for the driver separation guidelines are presented in the literature for circular drivers. These cases are:

1. Far Field. Ureda [3] uses driver directivity to determine that circular drivers need to be positioned within one wavelength center-to-center at their highest operating frequency. Wavelength is equal to the velocity of sound (344 m/s or 1130 feet/s) divided by the frequency. Directivity of the multiple drivers in the line increases until one wavelength spacing is reached and starts to decrease beyond this spacing. Figure 7 illustrates how the sound wavefront is created by a line array. Spacing less than one wavelength creates a constant phase front but comb lines start to form beyond one wavelength separation. At two wavelengths separation the first cancellation occurs. Directivity continues to decrease with more severe comb line effects as the spacing increases beyond two wavelengths.

2. Near field. Urban, et al [1] derives a more restrictive criterion of no more than a half wavelength separation between drivers at their highest operating frequency. Fresnel analysis is used and a disruption grid is used to shutter a continuous line source in their work. This analysis is based upon their desire to place any far field dips (nulls) in the angle off axis response of the array beyond p/2 (90 degrees). This assures that secondary (off-axis) lobes in the sound field are greater than 12 dB down from the on-axis response (main lobe)...

For the tweeter line very close center-to-center spacing is difficult to attain as very small circular drivers would be necessitated for either the one wavelength or especially the half wavelength criteria. Consider operation to 20 kHz where one wavelength is 17.2 mm (0.68”) and a half wavelength is only 8.6 mm (0.34”). Without regard to their surrounding flanges, dome tweeters are available in 25 mm (1”), 19 mm (0.75”) and 13 mm (0.5”) diameters. Hence, with any mounting flange allowance at all, the one or half wavelength c-t-c criteria are very difficult—if not impossible--to satisfy at 20 kHz. But, if we relax the c-t-c criterion, more secondary lobes would appear in the 10 to 20 kHz frequency range. Fortunately, in this octave the ear is less sensitive (per Fletcher-Munson curves) so any secondary lobes likely would be less audible to the listener. Thus, if one wavelength spacing at 10 kHz is adopted as a compromise, then tweeter spacing would need to be 34.4 mm (1.35”) c-t-c apart. While more off axis secondary lobes would be generated in the far field, small flange tweeters are available to meet this dimension. The tradeoff is possible sound degradation from comb lines near 20 kHz.
Darkmoebius,

For the sake of brevity I did not go into as much detail. Yes it is true that a line array of woofers operating below 300 Hz is generally no problem due to the wavelengths of low frequencies. As you go up in frequency the problems start, unfortunately right in the mid range is where it can begin to be a problem.

It is much the same reason that some people argue that center channels are more trouble than they are worth....