Best way to hook up a sub?

Is this for a home theater or a hifi system?

If it's for HT, it's easy enough to hook it up. Just use the LFE output from the AV receiver or prepro.

For music, it's a bit more difficult. You might want to look at one of these boxes:

http://velodyne.com/product-accessories/management-systems/sms-1-digitalmanagement-system.html

It's always a bit difficult to integrate a subwoofer with main speakers. One thing I try not to do is to muck with the main speaker's crossovers. The speaker designers have put a lot of work into the speakers' internal crossovers so adding another crossover stage in front of it is going to muck it up further.

Something like the Velodyne helps you adjust the subs output to make sure it complements the main speakers by augmenting what it can't fill rather than using a separate crossover in front of the main speakers.

10-28-12: Doggiehowser writes
Is this for a home theater or a hifi system?

>It's always a bit difficult to integrate a subwoofer with main speakers. One thing I try not to do is to muck with the main speaker's crossovers. The speaker designers have put a lot of work into the speakers' internal crossovers so adding another crossover stage in front of it is going to muck it up further.

Main speakers need an electrical high-pass filter to prevent unacceptable IM distortion unless they're sealed boxes with a high cut-off frequency (80Hz is too low for drivers 8" and under) and even then you may want a steeper roll-off to work around your room's height mode that takes another pair of poles.

For reasonable integration where that's not the case the most reasonable thing is to plug any ports, replace the speakers' two high-pass poles with zeroes, and apply your desired high-pass function where a Linkwitz Transform will give you two zeroes and two poles using one op-amp, a biquad will do it in the digital domain.

A mini-dsp in the digital domain

http://www.minidsp.com/

or Linkwitz wASP (Linkwitz Transforms for both high and low-pass legs, another pair of poles in each to give you 4th order acoustic slopes, optional all-pass for the midrange, pads for a pair of notch filters) in the analog domain will do it

http://www.linkwitzlab.com/Pluto/woofer-asp.htm

You'll want to measure and neither is a plug-and-play solution.

I'm not a big fan of adding another crossover in front of the speaker's crossover.

I like the idea of running my main speakers full range and letting the sub pick up where my mains drop off. I ended up buying the svs pb plus 12. Im happy with it, I just notice alot of the bass I hear coming from my back right side corner of my room, no matter where the sub is placed, which is pissing me off. I ended up hooking it up to the left and right rca pre outs and Im using my xlr out puts for my amp. This seems to be working well with no ground loop hum.

Try downloading the Thiel SmartSub manual. There's a section on subwoofer placement.

I think centre between the 2 speakers is best for a single sub