Originally Posted by ergopower
Don, from your posts, originally you had a pair of L12s crossed over to your Maggies individually as a stereo pair. Now you run all your subs as x.1. Just curious why? You had commented that you preferred the ambiance from the stereo setup.
This will be long, sorry...
Why the change? It's complicated... There is the potential for bass cancellation and loss of some directionality using mono subs. Cancellation because, if the bass is for whatever reason not in phase in the L/R channels, then summing the two to a mono bass feed can lead to cancellation. That is very rare IME; most of the time the bass is (or is mixed to) mono anyway for various reasons. Directionality from two things, (1) crossover too high and/or slope too low (leading to significant energy well above the crossover frequency), and (2) potentially (been a while since I read the AES papers on this and I am not a current member) from the initial pressure wave applied to the speakers (e.g. the initial rush of air from a drum strike). Testing showed I am (was) sensitive to around 60 ~ 65 Hz for bass localization. My original system used a fairly high crossover and lower-order (12 dB/octave) so I could localize the bass. I put my single (DIY servo similar to Rythmik) sub in between before moving (much later) to stereo subs.
Fast forward a few years (decades, who counts?
) and now we have the HT revolution. While I had a number of AVRs (Yamaha, Sony, Denon) it was not until a few years ago that I got a dedicated media room and outfitted my more-or-less current system. The room is smaller than originally planned; we added a basement bedroom and associated hallway that not only sucked out a third of my floor space but also trashed my nice prime dimensions. Meaning I have some annoying doubled-up modes. I decided on stereo subs for historical (see above) technical and aesthetic reasons. My Pioneer Elite also had a quirk wherein LFE signals between the crossover point and upper end of the LFE spectrum were lost. The easy solution, sort-of, was to run stereo subs in parallel with the mains after an active crossover (set to ~60 Hz) so they looked like large speakers to the AVR. I played around with mono and stereo subs and frankly did not notice a difference, but after wiring in the crossover and all the amps left it alone. It sounded good.
When I moved to a processor last year (Emotiva XMC-1), it had options for mono, dual mono, or stereo subs. Naturally I tried all three. Did not really notice a difference. When I got another pair of subs (quest to resolve a room mode issue) I tried all three again, but setting up four subs was just way easier using a single mono output and tweaking phase on the subs, plus there are questions about the way multiple subs are handled by the processor (and by most processors, as it turns out). I could not hear any difference, or maybe thought I could once or twice but was never quite sure, and trying out different configurations and adjusting controls on the subs plus repeated runs of Dirac Live got to be way too time-consuming. So today mono it is!
It is also very possible that, in the primordial past, I did not take as much care in measurements (which took much more to do back then, no REW and USB mics), and the subs were not truly properly integrated. The vast majority of my time listening was using a single sub; stereo subs in my own system are a fairly recent thing. I set them up for others who could afford them, alas...
Now I am happy with my little quartet of F12's. I have a narrow null up around 150 Hz I am pretty sure I can fix if I ever get time to tweak again, but other than that the in-room response is pretty flat and 3 dB down around 7 Hz. I can live with that.
HTH - Don