Thiel Owners

Rob Gillum at Coherent Source Service might know. And some ebay, etc. resellers sometimes salvage old gear. Also, Madisound was still supplying some parts in the mid 80s and may have a clue. It was probably made (I don't remember for certain) by Vifa. But a stock driver will not work. The motor was custom designed and everything else was specified by Thiel. Normal woofers don't have the smooth high-end rollout needed for first order slopes.

@tomthiel

I bought some JL Audio subwoofers quite a while ago - and their CR-1 crossover (and an Anti-node DSP unit to use on the subs if I want).

I haven’t gotten around to really integrating them yet. Which again will be pushed off for quite a while.

Truly integrating a subwoofer seems to be a very difficult process. It seems to me so daunting because you are essentially, as a layman, becoming a speaker designer. Whereas the skilled speaker designer carfully selected drivers, crossovers etc to integrate the low woofer frequencies, you are throwing that away and saying "I’ll take over from here" below the low pass filter, say, 80 hz.

I have fretted especially about integrating a sub with Thiel speakers given the entire speaker was designed to be time/phase coherent...but if I’m going to add a sub at, say, around 80 hz down, then the exigencies of sub placement etc means I’ll lose the time coherence for the bass frequencies. Am I not right? That is, unless one is using DSP on the whole signal which could set up a proper delay etc between the subs/Thiel speakers.

How did the Thiel subwoofers maintain time/phase coherency?

Jim designed the subs with LXE controls to be used by "normal" subwoofer installers with their programs, etc. It is indeed very technical and must match the low-frequency roll off of the main speaker. That process is A: a headache rarely gotten right and B: protected turf of the knowledgeable installers.
Jim's patent was on the room boundary portion. Each Thiel passive sub XO was customized for a particular Thiel model to make the best available complementary crosspoint behavior between the main woofer and the subwoofer XO. The "Integrator" is even more sophisticated - I want one. The room boundary controls on the subwoofer tell it the distance from side and back wall to optimize and shope its output and low end roll-off, allowing room placement without concern for reflections, boundary effects and so forth.

I had tried and given up on subwoofers in general due to issues that you raise. Life is too short. However, the Thiel SmartSubs with passive XOs drop right in with no hassle. When I get my room tuning software up and running, I'll be able to fine-tune sub placement. Now they are same ear-path distance as mains, but XOs are never that kind, I'll probably have to tweak a little.

Thanks Tom.

My issue is that I simply couldn't use any of the Thiel subwoofers (despite that I sometimes see them for sale on audiogon!). 
My 2 channel listening shares space with my home theater set up, so the room is packed with speakers already, and the only place I have for subs is under my projection screen along the front wall - behind my Thiel 2.7 speakers.  The Thiel subs are all too large and would intrude in to the picture area, so I had to find the smallest subs I could buy, of good quality.  Fortunately the JL Audio E110 subs fit just right, and come with truly excellent reviews.

But...it is such a headache to do the whole sub thing right that I just haven't got around to it.  Some people spend frightening amounts of their time integrating subs. It's not uncommon for me to read "after several years I've finally got my subs perfectly integrated!"  Yeesh!

The 'sub problem' is what drove Jim to take the bass as deep as possible in each model - because subs are inherently difficult. Bass is a problem in most rooms, regardless of what makes it. Many manufacturers side-step the problem by attenuating the bass and complementarily the top end for easier room integration. One of the factors for migrating from sealed to ported (and passive radiator) bass is that the ported bottom dies faster and therefore stimulates room modes less.