That is the exact combo I have ... JBL 306mk2 with Tannoy TS10. That little TS10 sub is a gem IMO.
Cool.
Stock it sounds great but there was no output at 25 Hz & I wanted to be able to play back music that goes down to 16 Hz. I doubled the capacitance in the crossover to make like it had 25 Hz crossover & I bypassed the subsonic filter that cuts everything below 29 Hz. Then I D.C. coupled the power amp section to insure no loss of drive occurs at 16 Hz. Sub sounds just as good in the zone 30 Hz & above but now keeps going down & down with no loss of acoustical output at least down to 20 Hz.
One could probably do fine without D.C. coupling the power amp but to go lower than 29 Hz you need to bypass subsonic filter. There is a fair amount of music that has synthesizer bass lines that benefit from subs that have good output below 30 Hz.
Doubling the capacitance in this case does not actually lower crossover frequency. It just flattens the response below the resonant frequency of the subwoofer driver system. This resonance is between 45-50 Hz. Actual crossover still takes place around 70-80 Hz acoustically. Electrical output continues to climb until about 17 Hz at 12db/oct compensating for the acoustic roll off below resonance found in acoustic suspension bass drivers.
It still has all the positive character of the original TS10 sub. Absolutely great platform to modify amp & crossover. Only now I have every thing I want.
By the way I have been operating this subwoofer like this for many years. It is a very robust subwoofer system. Driver can handle a tremendous amount of bass. Far more than Tannoy allowed.