[rak313]

Danny.

I am pretty new  to speaker design and I am confused about your OB designs.  The only link I could find with a description of the theory was http://www.linkwitzlab.com/woofer.htm.  In this reference, he shows a 6 dB/oct gain that requires equalization to result in a flat frequency response.   

From the reference:
"The woofer requires electronic equalization of the 6 dB/oct frequency response roll-off which is due to front-to-rear sound cancellation."

Yet I don't see this equalization in any of your designs.  For example in the wedgies, or in the OB bass servos.  Did I miss it somewhere or is there some reason why it is not needed?

Thanks

Rick

[nickd]

Rick,
The OB servos have a compensation circuit built into the servo amp. The Wedgie only plays down to around 200HZ and is designed to mate with the OB servos. The mid-bass and lower midrange are supported by cabinet shape (the wings) and I would imagine a bit of Danny's crossover magic for incredibly flat response with very few parts in the circuit.

They are my next build, I am waiting for Danny to complete a matching Servo Woofer stand he has been working on. I want the slam of the 12's but my wife would like the space saving shape of the stands. Who do you think will get their way on that one?

[Danny Richie]

Rick, the servo technology is a completely different ball game.

It compares input signal to cone movement and makes on the fly adjustments to maintain a linear response. So our 12" servo woofers will play flat to 20Hz and hit a -3db in the teens all while doing so in an open baffle. They also have the ability to return to rest approximately seven times faster than an uncontrolled woofer.

They're game changers.

[rak313]

Danny,

After thinking more about this,  I understand how the servo can compensate because it has a sensor in the voice coil and knows it's for an OB design, but what about the wedgies?  Does that need the 6 dB/oct compensation? 

[corndog71]

That guy Linkwitz is a total hack.






(Just kidding)

[Danny Richie]

The Wedgie has a natural roll off to the bottom end that will allow you to run them full range with light power. If you want to really put some juice on them though, a high pass filter inline with your amp will be fine.



So your target crossover point will be just below 200Hz.

[rak313]

That guy Linkwitz is a total hack.


(Just kidding)

S. Linkwitz includes discussion, references, and equations on his web page.  I didn't find any other links that analyze their OB designs. 

Danny's wedgie has a large wing on one side, and a small one on the other, so it's not exactly the same thing.  And I don't blame Danny for not elaborating, as I don't see anyone else doing asymmetric wings, and maybe there is some magic in his design any he doesn't want to explain exactly whats going on. 

[mlundy57]

It looks to me like two different methods. Linkwitz uses active crossovers with separate amplifiers powering each driver while the Wedgie uses a passive crossover with a single amplifier powering all five drivers plus a separate servo bass unit.

I don't understand all of the technical details for what each part of Danny's passive crossover does but it appears that between the crossover and the cabinet design, cancellation effects are taken into account.

The graph is extremely flat from 300Hz out to about 15kHz where it starts to drop off and is only down about 3dB at 20kHz.  By crossing over a little below 200Hz, the 200Hz range, which is about 5dB down, would get a little boost from the bass units which would bring it up around 93dB putting the entire unit (Wedgie and servo bass unit) almost flat from 20Hz to 15kHz and -3dB at 20kHz.

What this tells me is that while the design and components are different from Linkwitz's, the objective of a flat response is achieved by the Wedgies and servo bass unit.

If I have this all wrong, those of you who know more than I do please chime in and enlighten me.

Mike

[Tyson]

The wing really allows you to have your cake and eat it too - it acts as part of the "baffle" allowing bass response to extend lower before roll off, but also at the same time allows the front part of the baffle to be very narrow, allowing much better imaging than is possible with a wide, flat front baffle.  Quite ingenious, really.  I'm surprised more manufacturers aren't copying it.

[Danny Richie]

Tyson really hit the nail on the head.

Without using the side wing to control and shape the response you wind up with a big peak from the front and back wave. And you wind up with an early roll off of the bottom end.

Linkwitz uses an electronic crossover to notch down the peak from the smaller baffle and then add boost in the lower range to gain back the step loss (basically). That approach adds parts to the signal path and runs the amp low on head room by forcing higher outputs down low to keep the response level. It also then requires an amp channel for each driver.

So if you know how to shape the baffle you really can have your cake and eat it too. And the Wedgie has high sensitivity that will allow the end user to drive it with lower cost small wattage amplifiers.

[rak313]

I don't really understand it, but I guess it's not necessary for me to understand it in order to hear its benefits!   And I don't like a lot of op amps in the signal path, so I like your design.

For the 3x SW-8-16FR and HX300 Amp bass servo - do you have an OB box design for it?   How about the 2x 8 ohm OB version you mentioned in one of the threads - are those woofers available yet, and is there a box design to go with it?  Sorry for all of the questions.

I must say - that frequency response looks damn good.

[mlundy57]

I don't really understand it, but I guess it's not necessary for me to understand it in order to hear its benefits!   And I don't like a lot of op amps in the signal path, so I like your design.

For the 3x SW-8-16FR and HX300 Amp bass servo - do you have an OB box design for it?   How about the 2x 8 ohm OB version you mentioned in one of the threads - are those woofers available yet, and is there a box design to go with it?  Sorry for all of the questions.

I must say - that frequency response looks damn good.

Yep. I don't understand it either but I sure do like listening to them.

A side benefit I have noticed is that movie dialog is crystal clear with just the left and right mains, no center channel speaker required.

Mike

[Tyson]

It mystifies me why more people don't use this approach - maybe it's too new?  But then again, I'm mystified by how  few manufacturers use Servo OB subs.  They are also fundamentally better than any other bass system I've ever heard (after 10 years of RMAF show coverage and a ton of local audiophile friends).  Just completely incomprehensible. 

[ACHiPo]

Well I might as well add one more variable to my head scratching search for smooth bass response in my listening room, so a dumb question:  Where do I find out more about servo OB subs, amplifiers, plans, etc.?

Thanks,
AC

[bdp24]

I don't really understand it, but I guess it's not necessary for me to understand it in order to hear its benefits!   And I don't like a lot of op amps in the signal path, so I like your design.

For the 3x SW-8-16FR and HX300 Amp bass servo - do you have an OB box design for it?   How about the 2x 8 ohm OB version you mentioned in one of the threads - are those woofers available yet, and is there a box design to go with it?  Sorry for all of the questions.

I must say - that frequency response looks damn good.

Rick---Danny's cabinet collaborator (Danny makes the drivers, kits, etc., but not cabinets and enclosures) is a woodworker named Ruben (AudioCircle "name" Outofthewoods). He has some threads here picturing the OB sub H-Frames he offers as both flat packs and as completely assembled and finished products (for non-Do It Yourselfers). Ruben has an OB H-Frame design for both two 12" woofers and three 8's. Look in the threads here on the GR Research AudioCircle forum. Look also at the woofer listings on the GR Research website, where Danny has both W-Frame and H-Frame plan drawings with dimensions. If you have any experience with a table saw, etc., they're not too difficult to build. If you don't, Ruben will make you a pair for a reasonable price. Either way, you have definitely come to the right place for OB subs!

[Danny Richie]

Well I might as well add one more variable to my head scratching search for smooth bass response in my listening room, so a dumb question:  Where do I find out more about servo OB subs, amplifiers, plans, etc.?

Thanks,
AC

Here is where you can learn more about the servo technology.

http://www.rythmikaudio.com/technology.html

[Tyson]

To follow up, you get faster and cleaner bass with OB Servo for 2 reasons, and both have to do with controlling overhang, where the bass sound continues past the point of the original signal. 

1.  The first is the servo technology itself.  A servo will stop the woofer from moving much sooner than a non-servo system.  This prevents bass lag which is what leads to bloated bass.

2.  The 2nd reason is the OB approach.  Using an OB bass system causes far fewer room resonances to be excited.  A room resonance is a bass signal amplified by the room dimensions and occurs significantly after (and lasts much longer) the initial bass note.  So with a box bass system, the room itself is obscuring and "slowing" the bass.  OB is a much better solution for bass in almost every room. 

Between the OB and the Servo, you get a bass system that is both objectively and subjectively better than what is possible via other approaches. 

[Odal3]

Tyson - thanks for sharing the explanations and your impressions, which are particularly nice for us who dont have the opportunity to visit the audio shows. Been meaning to ask for a while which OB servo sub setup you like the best (W, H?) as well as driver size and qty.

[Tyson]

I like H-frame and dual 12 inches best - goes lower and louder than the triple 8 inch, and is still the perfect size to act as a "stand" for a midrange and tweeter. 

[rak313]

Rick---Danny's cabinet collaborator (Danny makes the drivers, kits, etc., but not cabinets and enclosures) is a woodworker named Ruben (AudioCircle "name" Outofthewoods). He has some threads here picturing the OB sub H-Frames he offers as both flat packs and as completely assembled and finished products (for non-Do It Yourselfers). Ruben has an OB H-Frame design for both two 12" woofers and three 8's. Look in the threads here on the GR Research AudioCircle forum. Look also at the woofer listings on the GR Research website, where Danny has both W-Frame and H-Frame plan drawings with dimensions. If you have any experience with a table saw, etc., they're not too difficult to build. If you don't, Ruben will make you a pair for a reasonable price. Either way, you have definitely come to the right place for OB subs!

Thanks for the advice.

I already have purchased a kit of a pair of duel 8" for a sealed servos from Rythmik.  see http://www.audiocircle.com/index.php?topic=112798.msg1316435#msg1316435. And about a year ago I was well on my way to finishing a pair of stands http://www.audiocircle.com/index.php?topic=126451.msg1334003#msg1334003 that would incorporate the servos when I got sidetracked.  I am just now getting back to that project.    What I would be interested in for OB servos would be either triple 8" (16 ohm) or dual 8" (8 ohm) versions.  So I am interested in a drawing so I can build it myself.  Ruben does incredible work, but these look pretty simple and within my capabilities. 

Of course, I don't really need these, as I have a pair of LS-6s and a LS-C, but the wedgie thread has me fascinated. As for the servo, I'm completely sold.  For about a year now I have been using a single 2x8" MDF box with the Rythmik HX580 that completely blows me away.  It replaced a 13" SVS PB ultra (which could shake my 25' x 15' x 6.5' to 14' cathedral ceiling room to the point of being scared), and I haven't missed it.  The servo is phenomenal.