[Pampero]

^ I agree. It isn't common to achieve a good crossover geometry when drivers overlap in unintended ways. I can see how adding low frequency energy below the useable response range of a speaker's woofer(s) could be accomplished in a relatively seamless manner but that would entail carefully matching the crossover's low pass, level and phase response at a point where the main speakers have no useful output. As soon as you opt for a knee that occurs above the natural roll off of the main speaker you start to have unintended/uncontrolled interactions between the two devices. This will result in additional artifacts that will most likely result in bloat, cancellations and time displacements or a hole in the response curve that defies solution without additional filtering. One may prefer the added warmth of a subwoofer when matched to the mains using only the low pass in the sub, but it is not likely to be a very accurate pairing. If a good quality crossover like the CR1 is employed, the system will be much better aligned than it would be without. It's that simple. This not to mention how much easier it is to achieve proper level and phase adjustments when you have all the tools you need and have the freedom to select the best point rather than one dictated by the mechanical limitations of the system.

It may be that one will be completely satisfied adding a touch of LF reinforcement below the roll off of his primary speakers thereby saving the cash for something else, but the freedom a proper crossover gives the user to balance the sound precisely isn't often achievable using just the low pass on a powerful sub such as a Fathom. The more low frequency energy your main speakers produce, the harder the job will be to accomplish without the proper tools. 802D3s probably fall into that category. I would think they have very good native LF extension. This lends even greater complexity to creating a blend that takes advantage of the system's full capabilities. One will have many fewer options in selecting the crossover point between the two devices which also limits the ability to experiment with varying crossover frequencies.

Not having a crossover in a design that requires one equals energy in the wrong places, not enough where needed, unwanted phase/time and frequency response artifacts, a long shopping list of potential problems.

I think not including the high pass element as a standard feature in the sub itself is the Fathom's biggest disadvantage compared to subs that include a true crossover section in the standard package. It's a bit confusing because JL includes just such a capability in their E series "economy" subs but don't include it in the higher cost Fathom series. It caused me some moments of doubt when looking for subs but I settled on the JL's anyway for their other virtues. Yet I can agree with the advice to try the Fathom without a crossover first to see if you can satisfy yourself without going to the added expense. If you're anything like me though, you will end up with a crossover and be glad you did.

I have 2 F113/V2 and a CR1 mated to a decidedly full range pair of Salon 2s and can link you to my experience which I detailed on the forum some time ago but that probably isn't necessary. Suffice to say it took the crossover to make my package provide the tight and extended bass it now produces. Getting great bass in a typical home environment seems to take it all: careful placement, precise matching of elements, some understanding of small space acoustics and the concurrent requirement for planned treatment that makes the difference in the finished product.