[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

[tomlinmgt]

I picked up a pair of Triple Threats a few weeks ago, but only just last night got to try them out for the first time. A friend loaned me his Lii Audio F15/W15 OB's to evaluate and that's what's currently set up in the system, so that's what the Triple Threats were paired with.  Time was a bit limited, so I really only got to try them out in one location... right next to (outboard of) the Lii OB's which put them about six feet out from the front wall and four or so feet from the side walls. The Lii OB's use wings for the W15's and they actually sound very good with all of the positive attributes  of OB bass down to around 80Hz,  but below that lack the sort of dense, robust, physical, room commanding low end I'm getting from the four 15" drivers in bass bins...which comes as no surprise (for obvious reasons).  Adding the Triple Threats with a crossover point on the plate amp of around 70 Hz and filters set first to EXT/12 then to 80Hz/24, rumble off, extension set at 20 and medium damping, I got some fairly satisfying, physical bass that comes close to what the bass bins provide especially as SPL's got into the low to mid 90's, but the drivers in the Triple Threats are really working hard at that volume level with a lot of excursion and I could hear audible distortion from them as SPL levels got pushed beyond mid 90 db...just when it was getting close to being in the room with a real kick drum.

The Lii OB's are filtered with an Ashly active crossover (biamped with Threshold s/300 on the F15's and White Oak Phase Linear 700B on the W15's transitioning around 225 Hz) and I don't have a way to high pass the W15's, so there is some overlap between them and the Triple Threats from 70 Hz down.  But I wanted to hear what sort of chest thump the Triple Threats could deliver, so I kept the crossover on the plate amps set to 70 Hz. I'll play with settings on the plate amps and location of the sub arrays in the room some more before I draw any conclusions, but I fear the Triple Threats won't satisfy my low end desires and demands by themselves...which pretty much everyone here told me would be the case. 

[Tyson]

Try setting the extension filter to 28hz on the triples and then bring in some sealed subs underneath that.  That might give you the best of both worlds.  Worth a shot!

[Early B.]

Yeah, you gotta play around with the settings a lot to get them right where you want them. This could take weeks or months of tweaking. And 70Hz on the plate amp doesn't mean you're crossing the subs over at 70Hz. Plus, you shouldn't get a lot of woofer excursion with distortion at low to mid 90's. Those darn settings need to be changed.

[tomlinmgt]

Yeah, you gotta play around with the settings a lot to get them right where you want them. This could take weeks or months of tweaking. And 70Hz on the plate amp doesn't mean you're crossing the subs over at 70Hz. Plus, you shouldn't get a lot of woofer excursion with distortion at low to mid 90's. Those darn settings need to be changed.

Yes, I'm aware that the 70 Hz crossover isn't a sharp chop at 70 Hz and -24db isn't crazy steep either...and I have no clue what the curve for the W15's looks like in my room. At this stage it's all just a starting point with guestimations based on the relatively short amount of time I've spent with the Lii Audio drivers and listening to what's happening with everything combined. I kinda figured there's a good chance I don't have optimum settings on the plate amps or even location of the sub arrays in the room. Rarely do I ever hit a home run the first swing when I try something new in my system.  It almost always takes a good bit of tweaking and experimentation, especially with speakers and subs. And the Lii Audio open baffle speakers may not be the best main speakers to be using with the Triple Threats for my first attempt since there's a good bit of overlap. I should probably be using something that I can high pass using the outputs on the plate amps.

[Early B.]

Yes, I'm aware that the 70 Hz crossover isn't a sharp chop at 70 Hz and -24db isn't crazy steep either...and I have no clue what the curve for the W15's looks like in my room. At this stage it's all just a starting point with guestimations based on the relatively short amount of time I've spent with the Lii Audio drivers and listening to what's happening with everything combined. I kinda figured there's a good chance I don't have optimum settings on the plate amps or even location of the sub arrays in the room. Rarely do I ever hit a home run the first swing when I try something new in my system.  It almost always takes a good bit of tweaking and experimentation, especially with speakers and subs. And the Lii Audio open baffle speakers may not be the best main speakers to be using with the Triple Threats for my first attempt since there's a good bit of overlap. I should probably be using something that I can high pass using the outputs on the plate amps.

Yeah, and you've got a large room to powerfi, so you'll encounter some limitations when you crank it up with only two lonely triples. It's a good problem to have because the solution is more subs.  

[tomlinmgt]

Try setting the extension filter to 28hz

Just so I'm clear on exactly what each of these filters is doing, I assume the extension filters are like a high pass...so that if the switch is set to 28 Hz, there is no information below 28 Hz (or 14 or 20) going to the sub drivers...correct? 

And the low pass filters are for a low pass at 80Hz or 50Hz with a -24db slope so that the transition from the upper operating range of the sub drivers to the mains is occuring at either 50 or 80 Hz...correct? What is happening at "EXT/12"?

Rumble filter is for filtering out the really low (like infrasonic) stuff...I assume.

And is damping an adjustment to the plate amp's damping factor?

[tomlinmgt]

Plus, you shouldn't get a lot of woofer excursion with distortion at low to mid 90's. Those darn settings need to be changed.

To be clear, the distortion doesn't emerge until I push SPL's beyond the mid 90's...up around or close to the 100 db point where a bass drum strike has sufficient energy that physicality and volume are getting up to live music event SPL's. But it was the content down around 40 Hz and below where I heard the distortion and saw the excessive excursion. The track I was listening to is called "Pillar 1" by Andy Akiho from the Seven Pillars release.
https://youtu.be/FsiF8tbwJR0?si=P8kLNCZDAYPNHbdY

[Bodhi]

I like GT Audio Works OB active subs. Those subs are well sorted and use new drivers and AudioControl RS1000 external bass amps. Unfortunately I can't fit a pair of them (incl: the bass amps) in my apartment, so i'm going with a single Rythmik F12SE sealed servo sub. But if I moved into a house, i'd upgrade to Greg's OB subs for sure (see pic below).

[Early B.]

Just so I'm clear on exactly what each of these filters is doing, I assume the extension filters are like a high pass...so that if the switch is set to 28 Hz, there is no information below 28 Hz (or 14 or 20) going to the sub drivers...correct? 

And the low pass filters are for a low pass at 80Hz or 50Hz with a -24db slope so that the transition from the upper operating range of the sub drivers to the mains is occuring at either 50 or 80 Hz...correct? What is happening at "EXT/12"?

Rumble filter is for filtering out the really low (like infrasonic) stuff...I assume.

And is damping an adjustment to the plate amp's damping factor?

Not sure if this is helpful, but it's all I got...