[tomlinmgt]

I've built a few non-servo controlled h-frame subs in the past using both Alpha 15a and AE Dipole 15, so I'm somewhat acquainted with the sonic characteristics of h-frame OB subs.  Despite all of their merits, the one major shortcoming I had trouble coming to terms with is their inability to reach higher SPL's below around 40Hz. In a 20x22x8 room, I could maybe achieve SPL's in the high 80's with the Alpha 15's and low to mid 90's with the Dipole 15's...far from being able to meet my objective which to approach or recreate a live music event (drums and percussion, in particular since I'm a drummer).  I understand that the 12" servo drivers have a good bit of excursion and are well controlled/powered by the servo feature, but without any sort of box loading is it unrealistic to expect them to meet my objective? Would a double trouble or triple threat get me there in a 19x26x vaulted ceiling to 14' space? I'm currently using a pair of JBL 4648 bass bins which gives me a total of four 15" high sensitivity drivers (2226) with extended ports to lower port tuning frequency to around 30Hz.  With around 300wpc, they can play over 100db at 30 Hz with no evidence of strain, so that's where my personal bar is set.  Seismic infrasonic bass isn't such a high priority for me, but it would be nice to have good extension into the lower 20's. But for certain, I want to be able to recreate the tactile sensation of a bass drum or deep pipe organ note like I can with the ported bass bins, but obviously with the merits of OB bass (musical, textured, no box coloration, less room interaction) and without the issues of bass from a boxed enclosure.
Also, what is the reliability record for the servo amps? And are they serviceable by a competent tech in the event they ever need repair?

[Huskerbryce]

I have 2 double trouble OB subs.  My room is smaller 19x26x9.  I employ 3 sealed servo 15” subs to compliment my OB subs.  However, during music applications I sometimes only run the OB subs.  During many music recordings they sound way more “musical”.  During live concert listening I turn the sealed subs on.  They provide the room loading you would expect.  As far as SPL, I have never tested the OB subs to their limits but I do know 100db is easy to hit.  You would be very happy with them for music.  Id keep your big ones to blend in the low low end.

[Early B.]

I have three double troubles in a 13x20 room and have no problems hitting 20Hz. For your room size, I'd recommend a pair of triples and an additional pair of 15" sealed servo subs in the rear when you really want to rock out. GR Research OB servo subs are the best option for music, especially since you're a drummer and want to hear all the nuances of life-like drums. I'll bet they'll surpass the sound quality of your previous H-frame sub builds, even the venerable AE dipole 15.

[Glady86]

What about two OB six pack towers  like others recommended, you probably need the big bass bins plus triple OB subs.

[JCarney]

HAL at Hollis Audio Labs has made modular open baffle frames that use the GR drivers and Rythmik amps so you can add drivers as needed. I provided a link so you can at least see the frames.

https://www.audiocircle.com/index.php?topic=189217.0

JCarney

[Glady86]

I have the modular type subs. Only have two per side or doubles. Nice way to start, then you can add more if desired. They bolt together.

[Tyson]

The Servo's definitely have more output than the Alphas.  I run the doubles in my upstairs system (music) and the triples in my downstairs system (HT). 

For a space like yours the triples might be enough but it'll be close.  If you really want to be safe I'd add a sealed 15" sub in the back of the room.  Or the suggestion for a full array of 6 servo's will get you there, overkill is my favorite mode.

[tomlinmgt]

Thanks for all the info, fellas.

Many of you recommend one or a few sealed subs to assist the OB subs.  What do you feel would be deficient from, say, a pair of Triple Threats in a room the size of mine that makes you suggest using box subs with them?  I have a pair of 15" Dayton Reference HF subs and enclosure flat packs I've yet to put together, so I have the helper subs if needed...but they aren't servo controlled.  Any issues with mixing OB servo drivers with non-servo drivers in boxes?  Here's a pic of the room to give some idea what I'm working with...

[Huskerbryce]

If you are listening to studio recorded music or even live music in a two channel stereo setup, two stacks of OB servos will sound phenomenal.  During movies and live concert videos it will still sound amazing but in my experience a sealed sub loads the room differently for those big bass moments.  The deficiency would be that “pressurized” thump feel you experience in an Arena at a live concert or in a movie, when a massive explosion happens.  The sealed sub will give you that extra punch in those moments.

[Early B.]

If your budget can handle it, put four triples in that room.

You'll get differing opinions, but I'd avoid mixing OB servo with sealed subs for a simple reason -- they sound different (been there, done that...). I recommended augmenting your system with sealed subs earlier in this thread strictly for budgetary reasons. However, with OB servo subs, more is better. 

P.S. -- that's the nicest listening room I've ever seen!

[tomlinmgt]

If your budget can handle it, put four triples in that room.

You'll get differing opinions, but I'd avoid mixing OB servo with sealed subs for a simple reason -- they sound different (been there, done that...). I recommended augmenting your system with sealed subs earlier in this thread strictly for budgetary reasons. However, with OB servo subs, more is better. 

P.S. -- that's the nicest listening room I've ever seen!

Thanks for the compliment. I'm probably equally enthusiastic about acoustics as I am hifi, so I maybe take it a little further than most. Suffice it to say, the effort pays off handsomely every time I sit down for a listen.

That said, building that room was a bit of an investment, so unfortunately the budget can't support four triples. I'm sure it would be extraordinary. Sigh