OK now we're getting somewhere. The box vibration was much of the problem in the midrange. It's not accuton mids, but the midrange tone is not distracting anymore.
I added 4 braces per box. 1 side to side in the bottom section below the ports, one front to back in the bottom below the ports, one front to back below the woofer. Then one side to side between the woofer and horn. There's not really any other opportunity to add more permanent cross braces. I need some front to back cross bracing between the woofer and horn as I can still feel significant vibration there where only a thin strip of wood between the driver holes is resisting the woofer motion and pressure. If I glued braces in there it would jail in the woofer. So I have to devise something removable, without screws showing on the outside. Maybe some brackets or something, or just wedge them in somehow to flex the front baffle outward and hold it out in tension so it can't vibrate in and out.
I fine tuned the speaker positions and toe angles with tape measure and adjusted the horn levels for center image using mono recording. The couch was 3 inches off center. With horns crossing about 2 feet in front of me the imaging is excellent. Big thanks to Carl for once again setting my speaker positioning ship on the right course.
The crossover is traditional LR2, which requires the crossed drivers to be out of phase, but it doesn't matter which is reversed. The published design has the horn reversed. I think tweeters should be correct polarity. Imo, ideally LR2 should be a three way so the midrange is out of phase and bass and tweeter can be right. Reversing polarity at the speaker posts changes both drivers, and the speaker sounds more natural to me overall. But the bass is a little weird occasionally. It sucks air when it should blow on kick drum and bass plucks, but it is a lot less distracting than weird treble.
The bass ports are too loud. With Sonos Bass EQ I can pull out 5dB and it sounds about right. Turning up the horn knob just makes the mids recede. I think I can add more internal damping to reduce the efficiency of the bass. If I put it down in the bottom near the ports and away from the woofer hopefully it will damp the ports more than the cone itself. The ports are contributing power up into the 200-300 area, so chilling them out will improve lower midrange clarity too.
So after all these changes it sounds a whole lot better. Definitely into the audiophile territory now. More tweaks tomorrow.
I played Colbie Caillat for my daughter tonight, she gave them the thumbs up. I don't think she ever heard her music played on high end speakers, since none of my previous projects were.
Now my wife is sitting next to me reading a book tapping her fingers and nodding her head to the music without complaining about turning it down or change the song. The CD/horn is very easy to take.