Thiel Owners

The 2.7 has a huge electrolytic cap bank to roll off the bottom of the midrange where the 8" woofer wants to cross in.

Hi Tom,

Out of curiosity, since the 3.7 and 2.7 share the same midrange/tweeter driver, wouldn't the 3.7 should also has a large capacitor bank as well?  My guess is the need for a large cap bank because the xover freq. is rather low - probably aroud 200 - 300Hz to the bass driver on both speakers.

In a typical speaker if crossing over at 200Hz is required, the amount of cap is probably around 80uF to 100uF depending on various parameters.
I could see the use of electrolytic since using poly cap could be expensive if 100uF is needed.

Andy - same coax but higher crosspoint to the 8" 2.7 woofer requiring 416uF series blocks. 400uF electro + 15 PP + 1uF styrene / tin foil. The lower 3.7 crosspoint needs 226uF as 3x75uF PPs plus the 1uF S/T. ( no Es in the 3.7 signal path.)

As I've mentioned before, Jim wasn't alive to apply his typical methodology, which would have been using the coax he was developing for the 7.3 to feed the 2.5 just as the 2.4 had been fed by the 7.2 and the 2.3 and CS7 were co-developed.
That jujitsu of dropping the 3.7 coax into an 8"model 2 and calling it the 2.7 is not Jim Thiel methodology, but rather a way to use an extant driver in a fall-down product, creating a model 2 more similar to the 3 in performance and cost.

You are right, big film caps are expensive. Note that the 2.4 upgrade requires only 42uF series feed caps.

Your 7b have plenty of current at normal listening levels. In parallel, they can handle 1- 3 ohm speakers effectively. In my testing, I never could tell the advantage of the parallel setting, as my SPL is modest, rarely exceeding 80 DB.

Hi Tom,

Thanks for the info.  I was actually very surprised to find that large a value for the cap at 400uF+.  Is it because the intrinsic impedance of the driver is somewhat low?  Or is more has to do with the time-phase aligned nature of the xover?

Thanks.

Andy -  the circuits control the drivers for a net 6dB / octave slope all the way down, including the interaction with the top end of the port where another pole is added to the top end of the woofer xo. Various conjugate circuits are applied to counteract bare driver anomalies. Since the usable driver range extends more than 3 octaves beyond the crosspoint, drastic measures can be called for.

As I said, I doubt that Jim would have tried to cross that midrange with that woofer, requring so much attenuation. He would have developed a smaller midrange with a higher natural bass roll out, to better match the 8" woofer with less brute force required.