I think I agree with FirstReflection that the PC12-NSD is more sub than I actually need, but I am really attracted to its cylinder form factor and all the positive reviews I've read. A big boxy sub is just going to look strange in my room since it will most likely be at or near the same height as my TV stand, but concessions must be made in the name of Science....errr a quality aural experience. That being said, the Rythmik does seem like a more logical choice for my room.
If the PC12 works for you, get it, but I strongly recommend TWO, not ONE! I only suggested dual rythmiks because $1000 is less than $1400!
One question I have about the Rythmik is why exactly would I want to turn down (up?) and/or limit the frequency extension? I know the size of my room is the main factor here, but not much more than that.
The presumption is that pressure vessel gain will overload your room below 30hz and cause a bottom tilted, "sluggish" response, signatory of vented loudspeakers.
I'd be inclined to disagree. No harm in having extra headroom. Maybe go sealed because combined with pressure vessel gain you can squeeze response a bit deeper, although nothing sealed will provide meaningful response near that price IMO.
The main thing is that for good bass you need to be able to
1) Experiment with position
2) have multiple physical locations / sources loading the room.
3) Be able to equalize and measure. Sometimes you need to to tame down a rising response as much as 10-12db!!
The above three things are vital and any setup that ignores the above is a lazy, poor setup.
Can I safely assume by the lack of commentary that the Paradigm sub just doesn't have much info out in the world yet? I've heard some people say they love their Paradigm sub (usually higher end) and some people seem to think they are average at best. On paper though, the Monitor Sub 12 seems like a really solid performer, especially at the price I can get it for.
People who own subwoofers always think their sub is the best, especially if it lacks bass below 30hz because then they think it's super tight and fast. Paradigm subs use a lot of watts and small boxes but are inherently limited for those same reasons.
Let's consider the sub 12 for example. A sealed 12" driver being fed 1700 watts.
There's a few problems with this.
The high watts indicate to me two things
1) Low efficiency.
2) Lots of low end boost.
Unfortunately a sealed 12 is limited by volume displacement. Commercial subs like this also abuse protection filters, which takes away any advantage it may have in a small room as far as pressure vessel gain was concerned.
It's small, and it's a 12" driver. Anyone who hears it will think it's tight and accurate, even if all they're hearing is +10db response @ 60hz (seriously, never pay attention to anyone's "stick it in a corner and listen" subjective reviews when it comes to any bass below 120hz)
The thing that is keeping it in the race at this point is the small form factor and relative price to purported performance, but I may end up avoiding it simply because there is no first-hand info available that I've seen.
Small Form Factor. That's what sells. That's all the info Paradigm wants you to know.
As much as I'd love it to be, having two subs in my room is simply not an option unless I figure out how to make them into a bed
Then figure it out!
I really need to stick to bookshelf sized speakers and even that is pushing it to some degree.
While the room is small, there's still only so far a bookshelf, especially the typical budget bookshelf can take you in the lower midrange. A lot of the time people take excellent subwoofers, and then mate them to inadequate mains. Why even spend all that money on the sub???! And then people set their sub 10db hot to compensate, but that just sounds bad!
FWIW I do like Timoteo's HSU recommendation. While there can be some horn resonances heard at higher SPLs, the tuning for those drivers makes them better suited for mating to a sub, than the typical low sensitivity, "45hz" bookshelf that is popular.
My suggestion is still to strongly consider Ascend Acoustics.
Is there anything specific and (if at all possible) tangible about them that you guys didn't like and/or feel were outperformed by other speakers?
I've heard paradigm speakers a couple of times (but not the Signature series mind you) but i'm not expert on them. I don't think they really do anything all that great... some people like that wooly, intimate, blandish sound but to me it's kind of... fake.
I prefer speakers that, reasonably dollar for dollar, are a window to the recording and yes I understand that's often asking a lot. Of course we're all biased for whatever reasons so to you -
no one's opinion matters including my own.
Trust measurements to guide you to a starting point, and then
audition speakers that measure well with your own ears

- BE PATIENT and DO AUDITION!
Remember that a speaker that adds to a recording in its own unique way, is technically
removing from that recording. I can live with sins of omission (IE less absolte detail), but not always sins of commission (IE hot tweeter or mistuned bass vent)
For the last 2 daysI've been listening to these speakers in the nearfield:
EMP Tek E41-B Bookshelf Speaker
...and while they
won't have the kind of output for anything worthy of being called an HT (only so far a 4" midbass can go) I can safely say that these wipe the floor with anything i've personally heard from Paradigm - stereo imaging, bass definition, midrange resolution.
Again, if your ears guide you to paradigm at the end of it all, fine, but if you're just buying based on a quick audition VS 2 other brands, or buying blind, then put some serious thought into it.
I'm not against buying blind either - if the measurements are decent then 30 day audition periods of internet direct brands are very good.
But you have to be able to live with the speakers. They're not a novelty, they're the window to the source material you'll watch whenever you want, so they shouldn't be a distraction!!
I'm
not going to say Paradigm speakers are bad because i can only say such a thing if you've got measurements to back it up -
my opinion is meaningless. I just recommend you exercise due diligence!