JL Audio 113 sub without external crossover

I own Eggleston Works Andra 2 speakers. I am doing exactly the same as you questioned.
That is, running the Andras full out and the JL-113 crossing over at about 55hz with a 12 db slope.
Once the Fathom 113 is calibrated it sounds extremly integrated with the Andras.

IMHO an electronic crossover would complicate or alter the sound purity. Not to mention more $$$ cables .

I agree with Ozzy. I am running the F113 crossed over between 50 and 55hz with my B&W 800's running full-range with no problems and well worth the performance attained.

I have tried it with and without an external crossover. Right now, I prefer using my NHT X2 crossover (only $300.00)w/ XLR inputs and outputs, with the high pass filter at 80Hz, with my Aerial 7Bs. While my Aerials are capable of in room response down to 25Hz, I simply get better bass performance from my F113. Although there might be a very, very small loss in transaprency, this is more than made up for by increased dynamimcs from my main speakers, having been freed up from low bass duties. The NHT X2 will also accept a LFE input if you are doing a combination 2 channel/HT set-up, as I am.

If you run your main speakers full range without a crossover, I don't how is sounds right unless you set the sub to kick in below your speakers lowest frequency range. If your ML Odysseys go down to 35hz and you set your sub to come in at 55hz, you're duplicating the 35-55hz range and I don't see how that could possibly be the optimal setup. If you can download the manual for the Descent, I think you will see that Martin Logan suggests setting the sub to come in BELOW the lowest frequency range of your mains when you run them full range.

Also, why do you believe that you need an external crossover with the F113, but not the Descent?