Do you use a Subwoofer when listening to stereo?

I’ve been spending the past couple days tuning a pair of REL S812s. It’s challenging because I have a mode around 60-70Hz, presumably the floor-ceiling mode. After a bit of tweaking, I think I’ve finally gotten the crossover low enough to avoid audible mode over-excitation. I can still see the mode on the RTA but I don’t notice audible distortion 

I set the crossovers for my usual listening SPL. I think if I played much louder, the mode would be more audible. 

Hello hsw,

     Are you stating that you're using a pair of subs and you're hearing or measuring a bass mode between 60-70 Hz at your listening seat? If so, this just means that at least one of your subs are positioned poorly in your room and in relation to your listening position (LP).  Apparently, your LP is in close proximity, or smack dab in the middle of, a bass room mode which is heard as a bass peak, dip or null.
     When utilizing 1 or 2 subs in a room, and the 'sub crawl' method is used to properly position them in the room and in relation to the LP, one of its major advantages is that this method ensures that there are no bass room modes in close proximity to the LP.
      I suggest you google the 'sub crawl method', utilize it to sequentially locate both of your subs.  Then adjust the volume and crossover frequency controls on both to the lowest settings you can while still maintaining bass performance that sounds good to you (it's solid, powerful, smooth, fast, detailed, dynamic, tonally accurate and it sounds natural).   Only once these steps have been completed,  would I recommend measuring your room to verify results.
     One or two subs in a room, provided they are optimally positioned in the room and in relation to the LP utilizing the sub crawl method, are capable of providing good bass performance, that is bass mode free, at a single designated listening position.  If you walk around the room away from the LP, however, you'll notice there are still numerous bass modes at specific spots in the room, heard as bass peaks, dips and nulls. 
    Utilizing 4 subs in a room in a distributed bass array (DBA) configuration in a room are also capable of providing good bass performance that is bass mode free.  But its main advantage is that it'll do so throughout the entire room and not just at a single LP. 
     If you walk around the room away from the LP after a 4-sub DBA  is installed, such as an Audio Kinesis Swarm or Debra DBA system, you'll notice there are no bass modes of any type perceived at any specific spots throughout the entire room.  

Later,
 Tim
    
    

No, and I never will. Now I do use one in home theater and that's where it stays. I'm not into the boom boom boom when listening intently to my stereo. 

No, and I never will. Now I do use one in home theater and that's where it stays. I'm not into the boom boom boom when listening intently to my stereo.

You might want to open your mind a bit on this.  Properly integrated subs can positively transform a 2-channel system.  Companies like Wilson, Vandersteen, etc. don’t offer subs just to add “boom boom boom.”  IME, once you’ve heard a system with good and well-integrated subs you don’t want to listen without them anymore.  They add much, much more than “boom boom.”

No, and I never will. Now I do use one in home theater and that's where it stays. I'm not into the boom boom boom when listening intently to my stereo.

With 4 subs there's no "boom boom boom" in my room.  If that's all you're hearing when you're listening to movies you could benefit from more subs and/or better setup and/or room treatments.  It's kind of like saying "I don't play vinyl because of the noise".