use only bass in 3 way speaker?

well I did something like that for fun about a decade ago, I just rotated the two alps pots in my JBL L-166 Horizons to zero so that just the woofer was playing.. faced it backwards.. and plopped my Spica's on top facing forwards.. it was an experiment shall we say. Sounded OK.

Thank you Duke and Xiekitchen. Regarding the crossover topology, I have no idea what it means so I better leave it alone. But thanks. Xiekitchen, I have no such controls on my old speakers, so as above I will leave it alone. I did not realize that it was so complicated. I will have to buy a electrical thingy that will only allow the bass speaker to work. Regards Peter

I dont like that idea.
Just sell the Isophons and get a real subwoofer.

I think you can drive your Isophons with a subwoofer amp, which would allow you to roll off everything above the subwoofer region. No modifications necessary, the variable low-pass filter in the amp, along with its other controls, would give you the tools needed to get a decent blend with your bookshelf speakers.

I've used bass guitar cabinets as subwoofers in a pinch, same basic idea.

Duke