bass does image above 80hz, and as far as i've heard, quad's do need a sub above 60 (up to 100 or thereabouts) to provide some impact and dynamics to the sound. x-over below 100(@ 60-80) will work, and probably easier, but you won't have much in the way of mid-low bass dynamics...that's the limit of the panels. and as jd97 points out, and correctly, front firing does(!) matter @ 100hz...but he's right in that from 60 down it doesnt.
and yes, the entec x-over just sucks. the best x-over i've heard is a passive RCA type x-over, ala audioconcepts (just a cap in line to the amp inputs), but made by TG audio...1st or 2nd order (forget which) at 100hz (custom built, @ $150), passive, and transparent...which few x-overs are. plug this x-over into your amp inputs, run the subs full range via a 2nd output from your pre, and the subs will naturally roll off @ 100hz (depending on the subs), while the x-over rolls off the mains @ 2db / octave starting at 100hz. works very well.
can't stress how important it is to get the last few hz...lots of stage and size comes with it. presentation just gets huge.
one more tip: elevate the sub, particularly front firing. even if its only a few inches, but better still if its 10" and up...decoupling from the floor reduces the 'muddy' aspect found in most subs...rosenberg mentioned this once..smart guy, gone too soon.
rhyno
