Thiel CS2

@sjbellers, the "Thiel Bass Equalizer" is intended to compensate for the natural bass roll off of the speaker enclosure by boosting the those frequencies affected by such roll off via equalized amplification to restore the bass extension that would otherwise be there. If you are not appreciating a difference there is a good chance that this old device, due to age might need some restoration. The difference with and without is not insignificant. You might be able to send your unit to:

Coherent Source Service – Specializing in repair and restoration of THIEL Loudspeakers

for restoration. FYI, there is promising rumor of upgraded new units that might be available in the future.  

^ The “MCS” is another stand mount Thiel speaker.

Amongst the most reliable and easy to drive of all Thiels. They do best with the typical Thiel recommended spacing. Though techincally amongst the easiest of all Thiels to drive, in practice it's a bit more challanging. Anything bright before them will be exposed, on the other hand the ported bass, though overall quite respectable, can be a bit soft.  With their 6 Ohm nominal / 5 Ohm mimimum 88 dB sensitivity they are not as current/power hungry as most other Thiels. They work best with amps with tight bass and soft highs and IMHO with mid hall perspective. That's not as easily found as might be expected, especially on the cheap.  Still high quality amps can be found reasonably. Though they can work with modestly powered 50-100 Watt p/c amps, they will demonstrate the benefits of added power up towards 250-300 Watts p/c. This might have been the Thiel speakers that had the most tube amp users. Despite many auditions I never felt that tubes did the bass right with them.YMMV!