Adding sub to Sonus Faver Guarneri Evolutions...need advice where to set crossover on sub


As the title say, I recently pulled the trigger on a Rel T/5i sub to pair with my Sonus Faber Guarneri Evolution monitors. Ultimately when funds allow again I will add another sub. For now, I only have 1.  I have a small room that is 9x10x9 with the back wall only being 3’ tall, above that the room opens up to my family room and kitchen. I listen at fairly low volumes, no more than 75dbs typically. The Evolution speakers start to roll off at 72hz and its -6db point is 43hz. Its -3db point is around 60hz. Any advice on where set the crossover on the Rel would be appreciated.
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I have the Sf Cremona Auditor Ms with a REL B1 sub.  A Sf rep suggested to me to set my Xover on the REL to 45Hz - he actually said for training purposes this model of Sf and REL were used by Sumiko as a test for their field personnel.
Thank you for the reply miner42.  I am not sure what the -6db freq is for the Auditor Ms but at least for my speakers that seems like a decent place to start.  I've got my test tones and SPL meter ready so I can see what kind of freq response I can get.

BTW, did you have any trouble integrating the sub with your Auditors?  Is the sound pretty seamless?

Looking at the graph I would bring the sub in around 50hz-60hz. Don't forget to try reversing the phase on the sub as well to see which sound more linear.

http://cdn.stereophile.com/images/112Sfgfig4.jpg


Cheers George