Need advice on adding subs

I want to thank everyone again for the help. Sorry for the late response. It's been a busy week at work.

As often happens when I post a question here, the answers expose me to the complexity of audio reproduction.

The other thread recommended some authors like Toole. I think I'm going to do some more reading on acoustics to better understand the nature of bass reproduction before I commit to a purchase.

  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

 I have some rudimentary DIY skills so I could probably manage a speaker assembly. I'm a bit cautious about the open baffle. I've noticed that a lot of people are experimenting with these type of speakers. But, audio has a history of technology fads that are initially celebrated but ultimately disappoint.   You have inspired me to get a little more serious about understanding acoustics. I think I need to study more before I start sinking even more money into audio.

I understand your trepidation regarding a new-to-you design (open baffle subs), cjk. But consider this: More than a few people consider one particular type of loudspeaker still the best overall of any yet devised: The Planar, one type of OB; Electrostatic, Magnetic-Planar, Ribbon. They have been on the market since the 1950’s, hardly a fad! OB subs are nothing new, but have long presented unique problems for designers and users, and have never become common, remaining a hardcore OB enthusiast cult item. It was Danny Richie’s vision of mating the OB sub principal with Brian Ding’s Rythmik Servo-Feedback design that has allowed the two gentlemen to solve many of the OB Sub’s inherent weaknesses (lack of output, low-frequency dipole cancellation, size), and create the best musical bass reproducer currently available.

Sound quality fanatics, particularly in Asia, have been using Magneplanar Tympani bass panels as woofers since Harry Pearson came up with the idea in the 80’s. The huge Magnetic-Planar drivers provide a quality of bass reproduction unlike that of any cone woofer. If you’ve ever heard a Tympani speaker, you know what I mean. Taut, transparent, with no-overhang or boom. The Tympani’s reproduce the sound of low register piano strings, acoustic bass and cello strings, and bass drum heads like nothing else! I bought a pair of Tympani T-IV’s specifically for use as woofers with my old Quads, finding no boxed sub to blend seamlessly with them, a common opinion amongst Quad owners. The GR Research/Rythmik OB/Dipole Sub has replaced the T-IV’s in my system. It’s that good!

But it’s not appropriate for every listener, system, and/or room. For those people, there is the Rythmik Sub, the next best thing. Call the guys at Sterling Sound and ask them for their opinion of the dozen F15’s in their mastering monitor systems. Brian offers 8", 12", and 15" models in both sealed and ported enclosures. Later this year there will be the new 18" model, at the request of Home Theater aficionados who appreciate the sound QUALITY of Rythmik subs, but want the output of the "monster" subs popular with the HT crowd.