Personally, I'd always try to cross a sub at somewhere between 70hz and 80hz or so. Note: I use an active cross-over and this observation may not apply at all to those who don't.
Getting the kick-drum fundamentals (typically 50-60 hz) directed to the sub has two great benefits, IMO:
1) A decent sub is typically much better suited to moving this volume of air and will do a better job of it than even an outstanding main loudspeaker.
2) Relieved of moving that much air, most main loudspeakers will sound better thru their entire bandwidth.
Per Erik's recommendation, using Room EQ Wizzard (or a variant) will help you dial in smooth response - that's true even if you're crossing higher. Even better, IMO is digital room correction and bass management (Audyssey, etc). Not audiophile approved, but a great solution for integrating a subwoofer IMO.
Getting the kick-drum fundamentals (typically 50-60 hz) directed to the sub has two great benefits, IMO:
1) A decent sub is typically much better suited to moving this volume of air and will do a better job of it than even an outstanding main loudspeaker.
2) Relieved of moving that much air, most main loudspeakers will sound better thru their entire bandwidth.
Per Erik's recommendation, using Room EQ Wizzard (or a variant) will help you dial in smooth response - that's true even if you're crossing higher. Even better, IMO is digital room correction and bass management (Audyssey, etc). Not audiophile approved, but a great solution for integrating a subwoofer IMO.