Line Array Speaker vs Point Source Speaker

That's quite a compliment Duke!

How do line arrays deal with "comb filtering", or is it not an issue?

Hce4, comb filtering in the vertical plane is dealt with by having the inter-driver spacing small in relation to the wavelengths produced, and/or using drivers that inherently have limited vertical dispersion anyway and therefore little or no overlap vertical overlap (like the full-height ribbons in the modules that make up the Dali Megailne).

In the horizontal plane, we want the inter-driver spacing as small a possible in relation to a wavelength at the crossover frequency. A steep crossover also helps to prevent lobing in the horizonatal plane by narrowing the frequency region covered by two drivers.

Some prosound line arrays have slot-loaded compression drivers flanked by a pair of midwoofers. The slot loading of the compression driver gives it a narrow horizontal footprint but wide horizontal coverage, along with narrow vertical dispersion (which minimizes vertical comb filtering) in a format that allows a fairly low crossover frequency so that the flanking midwoofers don't beam too badly in the horizontal plane in the crossover region. With the right crossover, it should be possible to avoid any deep nulls in the horizontal plane within the coverage angle of the array.

Duke

That's high praise for Soundlabs when it comes from your keyboard, Duke. One thing I've learned to appreciate from my line arrays (which you've listened to in my home)is their preservation of dynamics and detail at low listening volumes. It's counter to the oft-given kudos for high volume listening performance that arrays generally receive. The addition of outboard subs which can be dialed in for low volume output complementary to the arrays makes for one of the most satisfying low listening volume setups for me. Wife and neighbors agree!

Man, I have come to the realization that almost no one has heard an actual line source speaker. A line "array" speaker? Yes. 
    But that means very little.
  But not an actual "Line Array" speaker that can produce the actual "Line Source Theories, Cylindrical, Expanding Wave"?    No. 
 The closest you have heard is a line array. Producing what many call the, "Line source effects". And that? Is not even remotely close to what can be achieved with a correctly implemented Line Source design. Even if in the application of that design it is only 50% capable, "If that", in it's attempt at fully resolving the coherent primary wave which all are after.. That's about where I stand now I believe. And the results are damned astounding. And nobody has ever published it's "Actual" effects! Nor have I ever heard anyone even list them past the few that everyone talks about! And then dismiss them, because the far-field gains are only so much. And distortions can be lessened in another way as well....right? But there is more. So much more....And I cannot be the only one to ever find these "effects"? 
     In truth every line source design I have seen has at some point "Forgotten the original science behind and IN the theory itself". Especially when actually building a speaker, while using that theory as namesake.
      This means that they all are indeed NOT, what they call themselves.
   An easy trap to befall you as I myself fell into it. 
       I then pulled myself out and attacked every problem individually. And had some luck also I believe. Having studied Elec. Current Theories, Particle Physics and Viscous Flow all helped. As did others like Wave Mechanics and String theorem.  But it still all came down to listening....If anyone would like to listen I could arrange it.
       One thing everyone seems to forget though?
  When you build a point source? It is still a point source no matter where it operates.
  When you build an "actual", Line Source? It can only be that, dependent on several environmental criteria having been met. OR, It will simply de-fault and become a Point Source device.
   "Like when an escalator shall cease to move? It simply becomes a stair!
 These basics are written in the original theory. And subject to what I currently call, "Line Source Law". 
       Don't give up! Better things are on the horizon!
                    Scott