[thxgoon]

What are the THX specs again?

Off the top of my head I was thinking something along these lines.
90db 1w/1m
80-20khz

Is there anything else I'm missing, because if not, it won't take much to achieve those results.:huh:

The specs are not all made public, but wide horizontal dispersion with minimized virticle dispersion, high power halding and 12db/octave natural roll off below 80hz should get your sufficiently close in terms of design. Meeting those specs and building something that sounds good is the challenge :R

 

[thxgoon]

Does anyn have ideas on placement of acoustical foam (aka M&K) to better focus the highs?

I believe the foam is used to minimizes edge diffractions... but somebody here knows more about this stuff than me. Using a line array as you are suggesting will help to focus the highs.

 

[thxgoon]

Also note that that S150 used a different tweeter in the center of it's three tweeter array, which received a different output from the crossover. So it's not strictly a line array where every driver has the same signal. The top and bottom tweeters do receive identical signals.

It depends on which model of the S150. In the powered professional version the center tweeter is open back transmission line, otherwise they are all the same. The center tweeter does get a different signal than the outer two but I'm not sure how this works. In the newer models you can select the vertical dispersion pattern of the speaker and I think this works by attenuating the outer tweets.