Go with an 80hz crossover
now run some sine waves from around 120hz to 200hz at high volume through the sub
Listen for strange noises coming out of the port. If you don't hear anything unusual then there's no reason to worry about crossover point. If you hear something, go with a 60hz crossover.
Honestly, one should let the room decide what is the best xover to go with...
One may have capable mains, but in all reality his subwoofer will perform better handling bass even much higher then 80hz. Regardless, his measured responses should be the dictating number at which freq fits best for his particular room.... It really all depends on placement and room response. If he has a huge cancellation at 80hz it would not be wise to just randomly be choosing 80hz.
Many people make the mistake of letting their egos get in the way of choosing a xover.... they buy large main speakers that perform well down low, and then purchase a subwoofer to produce the really low stuff, but just because your mains go that low, doesn't mean they can do the job with the low stuff better then the subwoofers of todays very well designed and performing drivers.
I have Paradigm Sig S8's, but yet I xover at 120hz - We actually tested xover all the way up to 150hz but it just wasn't as clean a measured response for that xover as 120hz. I guess that would mean that I'm a fool and the S8's considered a waste, but in the way I have it setup, they act like a larger line array, and never have to work very hard.... In all reality I probably could have gotten smaller mains - oh well hind sight is 20/20....
My point - Don't use some arbitrary number to decide what you xover your sub/s to your mains - let the room decide by the final measured response.
