From previous posts all about mixing different impedance cabinets I decided to try isolating one cabinet with a crossover capacitor. The trick worked, the amp did not run hot and the isolated cabinet sounded fine. The only issue was that I had the cap value a little low and it removed a little too much bottom end from the the isolated cabinet. I used a 145 uF @ 250 volt capacitor. This resulted in a crossover point of about 180 Hz. I thought this might be ok based upon the fact that the slope of the crossover was 6db/octave. So I will now rig up a crossover capacitor of between 330 and 440 uf. this will make the crossover point between 60 and 80 Hz with the same 6 db/octave slope. Test results to follow. The isolation results because the amp does not "see" the load of the crossed over cabinet because the capacitor will not pass DC like a voice coil would do, effectively isolating the cabinet from the amp. Therefore if you have an 8 ohm 2x10 and a 4 ohm 1x15 and you want to run them together and your amp will not like 2.67 ohms then the cap is used with the 8 ohm cabinet isolating it from the amp which will then only "see" the 4 ohm cabinet.