help please

I am finishing up my Leach amp in the next week and at that time will get rid of the old plate amp and use the Leach to drive my sub. For reference, the sub is a shiva in a vented EBS alignment, exactly to the specs on Adire's website.

My question is this: Is a crossover necessary? I think that it might be, and would like to make it active if I do need one. I've been over all the projects at, but all of the sub circuits I see are equalizers. Are these sufficient, without a crossover? I know it's possible to modify the 2/3-way designs to drive a sub, but I don't know which one to choose, or how to modify it. Do you have any recommendations? I've also seen another circuit that John Pomman has,, that looks interesting. Can anyone comment on the quality of any of these?

I am looking for the best quality possible, and hopefully also have at least an adjustable fc from 60-100Hz. I talked to someone last spring who was also offering a similar active kit to the ones listed above, but I cannot find the link anywhere. His circuit also had adjustable phase. Help is greatly appreciated.
Hi Austin

Elliots Project 9 is a crossover. Marchand also sells very similar crossover kits.

The only negative to these designs is that to change the crossover frequency requires you to change several resistors (not going to do this with a pot). PRO audio crossovers do have variable crossover frequencies, but the designs are much more complicated. Rane is kind enough to publish schematics to all of their products online.

This will give you and idea how complicated doing this is.