I lucked out and snagged a pair of LS90s off CL that are in excellent condition. I already had a pair of Magnepans, but at the price I paid for the LS90s I thought I would play with them for a while, sell them and recoup all my money.
I thought they sounded really good at the seller’s house and even better when I got them home. Playing pink noise through them I was surprised to find the lower 2 drivers were the ones emanating the midrange frequencies...
Anyway, I downloaded both schematics from this site (thanks!) and decided to make some further refinements to my version 2 LS90s. I moved the midrange reproducers into the top 2 positions of the cabinet and put the bass drivers in the bottom 2 positions. This involved removing all four woofers from each cabinet although I suppose the same could have been accomplished by rearranging the wiring coming off the crossover board attached to the terminal cup.
I was pleasantly surprised to find a 1”thick front baffle and 4 braces in each cabinet. Not surprising were the cost cutting measures of utilizing stamped baskets and thin guage inductors. Over all this is a very well constructed speaker. I took out the 2 layers of fibrous “door mat” type material that divided the internal cabinet volume and rearranged the stuffing to better damp the internal midrange frequencies and to stop blocking the ports. I also removed the plastic trim from the from of the baffle for diffraction reduction.
Put it all back together and...WOW! Imaging and midrange detail are GREATLY improved and the bass is a lot more focused and defined. This project was well worth the 2 hours of my time that it used and it took a speaker that I thought was already pretty darned good to an entirely higher lever.
Oh, by the way... I sold my Magnepans and am keeping the LS90s. :D