Need advice on adding subs

Thank you all for the help.

There is a good thread currently running elsewhere on the site, under the simple title "Subwoofers" (I think). Duke of AudioKinesis and BDP24, among others, have made some valuable contributions, and it is worth reading. Here’s the link: https://forum.audiogon.com/discussions/subwoofer?highlight=subwoofers

That's a great thread. I had looked at that thread earlier and came away from it with some insights and some confusion.  My takeaway from that thread is this:

A sealed box gives the most musical and dynamic bass.  Using two subs instead one would let me crossover at a higher frequency.

That's why I was looking at a pair of Rythmik F12 or F12G. 

One thing that confuses me about that thread.  There appears to be a disagreement about aluminum vs paper driver.  That's the difference between the F12 and the F12G.  Can anyone clarify this for me?

Hello Martyki
Could you tell me more about the subs you used with the DeCapo

The deCapo is beautifully balanced as a stand-alone.  The presence thru treble is gently rolled off to balance the modest bass energy.  As a stand-alone monitor, it's really, really good and IMO one of the best values out there (which is why I bought mine).  When I added a subwoofer (for pretty much the same reasons stated in the OP), I loved the extra weight on the bottom end, but the sound as a whole went dull.  I tweaked it for a long time, but eventually moved on.  

  I agree the Decapo is a great speaker. Chamber music and jazz are great. But, I can't stand to listen to symphonic music on these speakers.

Hi BDP24
Wow. That's spooky.  I was looking at the Rythmik web site and the email notification with your post poped up on my screen.

You buy the DIY kit from GR Research or Rythmik Audio, the co-designers of the sub. It contains four 12" woofers (a pair for each of two subs) optimized for Open Baffle

Ok.  Open baffle? Is this a speaker with out a box?  Because that sounds like the opposite of everything I've read about subwoofers.  That is, that a closed box provides the best bass sound quality.  Ported boxes compromise sound quality to improve volume.

Cjk,

Unfortunately, this was some years ago and I'm not 100% certain of my timeline.  Over the last decade plus, I've used both Velodyne SPL subs and (the far superior, IMO) Rythmik 12" subs extensively (among others, less extensively) with many different speakers.  I still own both sets of subs, tho the SPLs have been relegated to non-critical uses.  I may have well tried both with the deCapo, but I can't swear to it.

In any case, I don't think it was the choice of subwoofer that did in the combo.  IMO, subwoofers work best with neutral to somewhat bright monitors.  I'd call the deCapo neutral to somewhat warm in voicing.

YMMV, but I eventually concluded that the deCapo works better as a stand-alone.  IMO there are numerous monitors out there that work better with subs .... probably because they weren't as skillfully voiced to stand alone.  Just MHO.

cjk: I think the take away re paper v aluminum is that the paper will sound more natural if you are solely using it for music and/or want to x over higher. I bought one that was delivered Friday as part of an experiment- a paper coned 12 in the ebony gloss finish using the xlr’d version amp.
The takeaway, as far as I’m concerned--others may have different views- is that multiple woofers even out the room response.
I have experimented with subwoofers for decades in my two channel audio and was never happy- trying to match them with Quad electrostats. Not only have the subwoofers improved, i think in part due to home theatre and car audio (JL anybody?), but it seems there is renewed interest in and thinking about high quality sub-woof’ing for two channel audio. A lot of what Duke wrote in that thread made sense to me in terms of "apparent" speed- sensitivity to frequency and volume, rather than just timing (if I’m remembering it right, it wasn’t leading edge timing that’s the issue, but ’stopping,’ among other things).
I’m also experimenting with DSP and a bigger old woofer- I have a bunch of Velodynes from the old days- an 18" (size of a coffin) and a 15"- both are well past their shelf life, but I DSP’d the 15" and am x’ing it over very low~ 45 hz. The Rhythmik is running without DSP, placed midwall on the opposite side in a corner-and crossed over a little higher-it’s a weird room. I got the levels matched at the listening position and have only enough loudness that they blend into the multiple woofers in my horn array. With some fiddling around-a few crude measurements, and some listening, moving, and listening, they seem to gel nicely and add a nice further dimension to my listening. I don’t listen particularly loud to begin with, but augmenting the bass--running as a parallel system, no high pass to my main system--has given the system more gravity and spaciousness, more music at relatively sane levels.
The moral, I think, is that these things can work, not just because the technology is better than it was 20 years ago, but because the strategies for placement and dealing with room interactions are more effective.
PS: I can't speak to the open baffle or dipole, one of the others can address. I know that using a dipole like a Maggie was one thing HP used to tout with the Crosby Quad back in the day, but I never tried it. A DIY build makes sense to me even if you have to get some help from a competent cabinet maker. Good luck and have fun. I certainly am, and it has added joy to an already good system.