Pair of Rel S510’s or Carbon Special’s?

I have been there and was an owner of the S510 and now JL. I have a few thoughts about your situation based on my experience:

1) The S510s are too small for a large room with large speakers.

2) I would try the DSP function to see if you can get what you want. Its free and easy. That would be a way better solution than subs. I do not have Roon, though.

3) I would be personally be inclined to take advantage of the Diablo’s sub outputs and get a different brand of subwoofer. REL company encourages high level inputs on their subs. Not the biggest deal. I found low level inputs are more user friendly, plus it eliminates any possible annoyance with pops and noise.

4) There is no substitute for positioning subs correctly. The room will dictate it. I do not know if you will be lucky. REL has an approach of coming in with the bass at a lowest volume level and frequency and time aligning with the main speakers based on moving the sub or speaker forwards or backwards. JL Audio is different in that the goal is smooth frequency response phase centered around 80Hz suggested crossover point and phase control setting.

5) The idea of ’speed’ (lack of resonance?) of the subwoofer does not matter unless the subs are well integrated in to the room.

I have both Carbon Limiteds and Carbon Specials in my two systems.

Both are wonderful and are so much better than my previous Paradigm subs and many I have heard.  I try to avoid the DSP.   I get the word ONLY in where they are going.  I said that.  But moving them one into the corner and one into the side made huge differences in eliminating room nodes.  Like you said and others, feather them in very slightly.  They add foundation and improve everything.  You miss them when they are off!

@ohlala thanks for your perspective.  Regarding the S510’s being too small for my large room and speakers, I think you are right.  But, the fact that I am not feeling the need to fully energize my room with bass, and just wanting to add a bit of slight bass support, that might make the S510’s okay for my application?  And, might make placement easier too, given that I plan to have their output set low?

@nyev 

 interesting subs and delayed phase feature, but to me it sounds like in my case I shouldn’t need a delayed phase feature since the subs will be practically in the same spot as my mains.

Mine are, too, but in order to deal with room modes, the adjustment on delay/phase is not identical on the two of them. After I positioned them, optimally, I then discovered that in order to get the best bass response, they need to be set differently; one wants to be at about 120 degrees and the other is at about 165 degrees. A REL would only allow 0 or 180.