2035 update...levels match pretty well using "12 dB Pi pad", 1.0mH/10uF LP w/ 4.4 ohm/10uF zobel...average LF level from 100 to 1000 Hz. was flat +/- 1 dB; from 2 to 11 kHz. the HF averaged about 1/2 dB lower than the LF, and from 8 to 16 kHz, HF averaged 1.5 to 2 dB hotter than from 2 to 11 kHz., and varied +/- 2.3 dB's average. HF F10 estimated somewhat more than 17 kHz...these were measured with the 4 Pi on the floor, and the mike about 2 meters away...mike height adjusted to put it in the "line of hearing" from the middle of the two drivers to the listening position, 12 feet away. hf readings averaged for the 8 to 16 Khz. response were "corrected" per data from a net posting.
Since I need to go in and replace the port tubes with shorter ones, I will "boost" the overall HF by about 1 dB, getting it 1/2 dB hotter, rather than cooler than the LF. And seal the HF horn flares to the front baffle...did not see puffs of air, but the newspaper slid under one end of each H-290, gotta be a leak there! a machinist straight edge says the H-290's are not flat...at least the fronts aren't! Drivers are sealed to the rear of the horns with a "certainteed" elastomer plumbing gasket...about 2.75 od, they just fit in between the two bolts. These are "done", and sound great...I'm just putting on the "auction wax" for that last 1% of "shine". Sam