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.

Cheers George

I agree with a 50-60hz starting point. But in addition to the phase switch the problem with Rel is the phase is either 0 or 180 degrees. The problem there is if the sub is leading or lagging the main speakers flipping the switch then they will only will then be lagging or leading the mains (opposite of the starting point). So what you have to do is either move the sub closer to farther from where you start. The most I ever had to move my B3 is 4". Once you get the phasing right it will be easier to set the crossover point and the gain. I start with the gain high when trying to determine the phasing.

Good luck and have fun
BTW once it's dialed in you should not be able to hear where the sub is located and the monitors will have a full range sound.

As you also said first pick 0 or 180 which ever sounds best then move the sub back or bring forward a few inches to get what’s in-between to further get it in phase.

Cheers George

Thanks guys. I am going to have to read up and get a better understanding of phase and how to test for correct phasing.  
@tboooe I just used my ears but will admit I thought I had it right a couple of times.
I followed the setup procedure outlined by REL.  My B1 integrates well with my Auditor Ms.  My phasing is at 0. 
Your OP question is very difficult to answer. I would suggest bringing in the sub at about 50Hz. This is where the SF's tend to get a little weak. However, the room plays such a large part, that experimentation ( and lots of it) is the word of the day, IMHO.
I have since repositioned by speakers and get my sub dialed in (I think).  In my room, I was actually getting good, flat sub response from 50hz - 40hz.  Once I spent some time moving my speakers around I get +- 2db response from 100-20hz, with a +4db hump at 40hz.  The mid bass and bass in my room is very tight and punchy.  Perhaps my hearing is not good enough, but I didnt find integrating my sub that difficult but I have never had "golden ears".