Your experience of moving to two subs

@soix Haven’t tried yet, but the Rythmik F12G is so much faster than the SVS SB2000 that it’s really in a different class. Is a different type of technology altogether.

My plan for when I try putting them into play together is to use a copper power cable on the F12G that I know sounds slower and more smeary and an 11awg 7N OCC silver power cable (which I normally use on the F12G) on the SB2000 to attempt to split the difference in apparent rapidity of response. Not sure if the SB2000 will get anywhere close in speed because of the silver, but my testing in the past showed that it was very responsive to changes in power cables. Much more so than the F12G.

@james633 I totally believe your anecdote. I also think I have a fortuitously sized and featured listening room for low frequencies. My experience has been far easier than the average report about using single subs that I've read. Nonetheless, I'm getting more and more interested in dual subs as this discussion progresses.

Gladmo,

you might be hearing a longer group delay that could make it sound “slow” I have not seen the SB2000 group delay but I was a bit surprised at how high the group delay was on the SB 16 Ultra (link below). It was over 20ms.  You could argue at that low a frequency it is less important but still about twice what JL does with their subs. The only way to overcome the delay is using an active system to delay the mains. Receivers can do this and same fancy highnesses as well.  Well a mini DSP does to but the output stage is junk.  anyway just a guess and thinking out loud. 
 

https://www.audioholics.com/subwoofer-reviews/svs-sb16-ultra/measurements

my 2 cents: you need money for 2 subs to try to 2 subs. My problem solved.

(I have one sub, purely because I lucked out, I could afford zero)

Never heard of the term group delay before, but maybe that’s it. The Rythmik sub uses a direct servo motor system to control transient response precision. The SVS in comparison sounds like the cone is slower to change direction. If it’s phase alignment that’s being referred to, I can confidently assert that it’s unrelated to my comments. Both the Rythmik and SVS have manual phase adjustments.