Thiel Owners

Beetle - a 3.7 upgrade is quite straightforward since the drivers are so well behaved, there is not much circuitry in there. The tweeter caps could be upgraded to CSAs with perhaps an ultra bypass around the 1uF styrene/tin. Electrolytics to film for permanence. Resistors to Mills MRAs. Film feed coil on the woofer. More upgrade for less cost than the more complex 2.4.

You'll see more from me after the Thiel Audio bankruptcy settles.

Tom

Regarding bass extension: I own the 3.7s and 2.2s. The 3.7s have been in my system ever since buying them last year and I'm preparing to sell the 2.2s.  I was noticing some "crackle" in the tweeter of one of the 3.7 speakers and decided to change out the 3.7 for the 2.2 in an effort to narrow down the problem. Turns out I had a frayed speaker cable. Here's the thing. My perception was that the 2.2 actually offered more realistic bass extension. I had one of the Bach cantatas on for reference. Bach uses just one contrabass, but it needs to be heard. I felt the 2.2 did this better. But, the overall texture of the recording was much better with the 3.7. I could hear the lute in the ensemble readily for instance. That was not so clear with the same selection rendered on the 2.2. Totally nuts, or what?
Todd

More upgrade for less cost than the more complex 2.4. 

The coax has separate XO for tweeter and midrange, right? Ie, not mechanical like the 2.4.

is this pic for all 3 drivers? Or just the coax?
https://hi-fi.com.pl/images/numeryhfim/2012-03/jpg/44-50_03_2012_07.jpg

Stereophile measurements actually indicate deeper bass extension with the 2.2 compared to the 3.7 (!), so your perception seems consistent with actual performance. Note that Tom Thiel still has 2.2s.

The 2.2 bass was our first passive radiator and as such it coupled to rooms better than anticipated and came out slightly under-damped and somewhat (1.5dB) higher in level below 200 Hz. It has the fullest bass of any Thiel product, which was warmly (ha ha) received by the public, but considered by Jim to be in error. Note the 1/3 octave Stereophile graph showing some excess bass. Notice also in the Stereophile review that the cabinet is possibly the quietest Thiel ever, including the new x.7s with curved panels. ( I have a fix for that 300 Hz and ringing, plus a hardening agent for the MDF baffle to increase rigidity. The 2.2 is the first (1990) cabinet designed from the ground up with in-house 5-axis CNC capability. I went wild with braces because they were so downright feasible! Note also the quality of the custom caps - those yellow styrene bypasses were from world-class German film / tin foil. The tweeter was our own from the ground up design for the CS5 - it is a powerhouse, even by today's standards. The woofer is the first iteration of the double cone with curved front and straight back. It is polypropylene with air core and works extremely well. That design became the basis for the present double aluminum with styrene fillet midranges. The most ordinary element is the midrange, but even that "paper" cone has polypropylene fiber reinforcement.

As you might guess, I don't feel the need to make many excuses for the 2.2. As Beetle mentioned, they are my workhorse which I use to critique recordings in the making.

Pops and others have expressed fondness for the pre-coax format. I agree that there is something simpler and cleaner in the wave launch. The coincident coax addresses a fundamental problem with first-order networks: vertical integration of the lobed radiation patterns. The coax solves it. But, IF you get your ear at the correct 35" up, the problem is solved at that listening position, obviating the need for the coax, which does introduce low-level anomalies of its own. The x.7 coax is better because the wavy surface spreads the tweeter-edge wave nicely.

Todd, you are not nuts. There are some significant strengths of the 2.2, and resolution is less in the the bass and midrange. The new caps and treatments will upgrade the overall performance considerably.

Beetle, the 3.7 XO pic you attached is for all 3 drivers. The mid and tweeter have separate motors (unlike the 2.4, etc.) with the midrange XO having the greatest part count (16 compared to 17 for woofer and tweeter combined).