Why are the Infinity IRS, Reference 1b, Beta ect speakers passive on the mids and highs?

I have not triamped these, I've never owned them.  I worked for Marcof/SpeakerCraft, we did alot of custom work and I got these to work on years later because of my time there. I worked on the crossovers only... Measured each ribbons output individually, then customized the pads within the crossover.  So without having complete driver measurements, that's why the basic design wasn't changed... better caps and coil or 2 and hand matched pads. 
For me, as long as your amps can handle driving ribbons (some cannot) and you have a very good crossover, this is a no brainer. 
It will take a bit to get these matched, but I would expect excellent results. 

partroysound: If your m/t panel wings move relative to the wings base as much as mine did, I would definitely attach a length of hardwood (or metal rod, like the Quad 2805 and 2905) to the backside of the m/t panel wing near its top, the other end secured to the wings base. A small hinge at each end would work fine. Those wood screws "securing" the wing to its base plate are woefully insufficient for the job. Then, an outrigger fitted to the bottom of the wings base plate will create a deeper footprint (the base plate is too shallow to provide front-to-back stability), locking the EMIM and EMIT drivers in space by preventing fore-and-aft swaying, for increased resolution and transparency. The bass enclosure can also use a wider footprint, again via an outrigger. These measures address and remedy the structural weaknesses of the RS-1b. The drivers and their filters is a whole 'nother matter.

I had a friend that replaced them with custom made active Xover much better depth,stage,bass detail,impact and dynamics.Good luck!!

Having seen a few fixes online, I have to say @timlub is most probably right.

These crossovers were done very "empirically" and I doubt any designer with modern measurement and simulation tools today would arrive at the same crossover designs. Most designers today would absolutely scratch their heads about the choices being made, as well as some of the impedance problems that resulted.

Active crossovers properly designed would be head and shoulders better than the originals, if only from being better measured and better tuned. :)

However, with good passive crossover design and good parts I think they could be brought up several levels today for use with your favorite amps.


Best,


E

I haven't finalized on the crossover points yet. On the tweeter 3500Hz to 4000 Hz is good, the low point on the mid is very tough. 150hz to 160hz leaves a gap to the bass modules. As I drop the frequency the sound doesn't change much until the EMIM's start to distort for being too low. I have tried a Tympani panel for mid bass 70hz to 135hz It sounds good but not a great look.
Marc