[Russell Dawkins]

That's a really interesting point Russell. I don't see the relevance of cone motion feedback in an open system.  Probably why SL relies on ASP/DSP to accomplish his goal.

Servo feedback doesn't make sense in any ported enclosure either, as far as I can see—only sealed.

[Davey]

Servo feedback doesn't make sense in any ported enclosure either, as far as I can see—only sealed.

Why not?
The objective is simply to try and make the cone accurately reflect the drive/input signal, yes?
This correction would not be invalid regardless of the baffling scheme the woofer is operating in.

I would stipulate it probably makes more sense in a closed-box (especially a small box) scenario since you have placed mechanical constrictions on the driver movements.

Dave.

[Shakeydeal]

Well I can't say whether it makes any sense or not. But I know that OB servo controlled bass is the best I have heard in my room, from either a subwoofer or full range speaker.

Shakey

[S Clark]

Well I can't say whether it makes any sense or not. But I know that OB servo controlled bass is the best I have heard in my room, from either a subwoofer or full range speaker.

Shakey

+1  It has been the top rated bass at the RMAF over a several year period.

[Tyson]

Go and listen to the Servo OB system used in the GR Research designs (Super V, Super 7, LS whatever).  I was a skeptic too, it made no sense to me.  But that's the cool thing about direct experience - it often contravenes your expectations. 

I'll leave it to others to argue about "why" it works.  I just know that I've heard some pretty crazy ass bass systems (ported, sealed, box, OB, Infinite Baffle, transmission line, passive radiator, swarms, servo sealed, etc...).  None of them sound as good as this OB Servo implementation.

It doesn't happen very often in this hobby, but on rare occasions you run across something that is just flat out better than everything else.  This is one of those instances. 

[schw06]

Go and listen to the Servo OB system used in the GR Research designs (Super V, Super 7, LS whatever).  I was a skeptic too, it made no sense to me.  But that's the cool thing about direct experience - it often contravenes your expectations. 

I'll leave it to others to argue about "why" it works.  I just know that I've heard some pretty crazy ass bass systems (ported, sealed, box, OB, Infinite Baffle, transmission line, passive radiator, swarms, servo sealed, etc...).  None of them sound as good as this OB Servo implementation.

It doesn't happen very often in this hobby, but on rare occasions you run across something that is just flat out better than everything else.  This is one of those instances.

I believe you and absolutely love the OB bass of my Spatials but I'm curious why nobody from the industry has made a finished stand alone OB servo sub for those of us non-DIY'ers?
David

[Russell Dawkins]

Why not?
The objective is simply to try and make the cone accurately reflect the drive/input signal, yes?
This correction would not be invalid regardless of the baffling scheme the woofer is operating in.

I would stipulate it probably makes more sense in a closed-box (especially a small box) scenario since you have placed mechanical constrictions on the driver movements.

Dave.

Dave, the ultimate objective is to make the acoustic output reflect the drive/input signal. In a sealed system that would be accomplished (in the very near field) by keeping the cone motion matching the input. I guess we have to ignore for this discussion the reduction in output with descending frequency due to coupling with the air. This varies with cone area vs listening distance, but is conveniently compensated by 'room gain' to some extent.

The servo system's attempt to keep the woofer's cone movement in lock step with the input would completely disrupt the tuning of the reflex cabinet. Don't forget that the reflex box is designed to lower the driver/box system's LF extension by resonating at a frequency below what would otherwise be the natural limit. At port resonance, the bass driver's movement naturally is minimal—if a servo correction system were to be introduced, the woofer would be made to move much farther than it should at port resonance and the output around that frequency would be much greater than was intended by the designer because you would be hearing the box resonating as intended, but added to the output of the now-linear bass driver.

In the case of open baffle, I see the advantage of servo feedback being the reduction of spurious resonances in the driver (ringing, for example) and suppression of the driver's fundamental resonance (fs). This would make the system sound cleaner through the bass range but would not in itself compensate for the progressive loss in acoustic output due to front-to-back cancellation. This, again, would be compensated mostly by 'room gain'.

Tyson, I don't doubt that Danny's servo OB system sounds great, but I think it is probably down to more than just the servo aspect of the design; there is a lot going on in the design of the amp driving those speakers. I would love to hear them, as I really love great bass.

[Early B.]

I believe you and absolutely love the OB bass of my Spatials but I'm curious why nobody from the industry has made a finished stand alone OB servo sub for those of us non-DIY'ers?
David

The price would be very high -- probably $8 grand or more for a pair of dual OB servo subwoofers, and no market for it. People willing to spend that kind of money are likely to want a simpler and more elegant freestanding speaker.   

[Tyson]

I wonder why more speaker manufacturers don't use it as the bottom half of a speaker system. It works phenomenally well on my Super 7's.

Especially things like Maggies or other planar speakers would benefit enormously from this type of bass foundation.

[Early B.]

I wonder why more speaker manufacturers don't use it as the bottom half of a speaker system. It works phenomenally well on my Super 7's.

Especially things like Maggies or other planar speakers would benefit enormously from this type of bass foundation.

This is the closest I've seen to what you're referring to:  http://www.spatialaudio.us/lumina

These speakers appear to use the Rhythmik Audio OB servo drivers and amps. Check out the prices and the weight, though.

[PDR]

I wonder why more speaker manufacturers don't use it as the bottom half of a speaker system. It works phenomenally well on my Super 7's.

Especially things like Maggies or other planar speakers would benefit enormously from this type of bass foundation.

I know why.....but if I told you I'd have to kill you......

[PDR]

This is the closest I've seen to what you're referring to:  http://www.spatialaudio.us/lumina

These speakers appear to use the Rhythmik Audio OB servo drivers and amps. Check out the prices and the weight, though.

They do seem to use the Rythmik, I wonder what drivers he uses, Dannys Paper cones?.
No pic of the amps.....they must match the baffles?

[Davey]

Highly entertaining how the crew here steered this thread from Linkwitz on OB to advertising for GR Research servo woofers. 

Dave.

[Early B.]

Highly entertaining how the crew here steered this thread from Linkwitz on OB to advertising for GR Research servo woofers. 

Dave.

That's because the resident expert on OB is GR Research, and the most impressive designs are the ones that use OB servo subs. Linkwitz lost me many years ago when he advocated the use of cheap multi-channel amps to power his designs, and his source at the time was a Walmart DVD player.

[mcgsxr]

Danny certainly has contributed a lot, and offers a nice commercial solution.

I happen to believe that the real value here is the collective wisdom kindly shared by so many.

Buy it or build it yourself, there are a lot of ways to audio happiness.

[Tyson]

I've also heard all the LW designs (yes, all of them) and if we're talking about bass, the LW design suffers from the same problem as every other full range OB speaker - musical bass that lacks punch and impact.  I only posted about the OB Servo subs because they are a better solution for people looking to build an OB speaker. 

[PDR]

Highly entertaining how the crew here steered this thread from Linkwitz on OB to advertising for GR Research servo woofers. 

Dave.

Entertaining? Glad we could make your day.

Stick around, later were gonna take over the full range circle....

[S Clark]

Back to the original quote:
 "It is difficult to screw up an open baffle speaker design to where it sounds worse than your typical box speaker." - Siegfried Linkwitz.

Proof that even smart people exaggerate for emphasis- or perhaps it's taken out of context.  If you read this to mean that some diy OB drivers thrown into a baffle will be better than a cheaply but professionally designed box speaker, I don't agree. 

[Tyson]

Back to the original quote:
 "It is difficult to screw up an open baffle speaker design to where it sounds worse than your typical box speaker." - Siegfried Linkwitz.

Proof that even smart people exaggerate for emphasis- or perhaps it's taken out of context.  If you read this to mean that some diy OB drivers thrown into a baffle will be better than a cheaply but professionally designed box speaker, I don't agree. 

I think he takes professional designer as a default assumption. 

[S Clark]

I think he takes professional designer as a default assumption.

Likely so. But I've heard some awfully good box speakers.  I remember the RMAF where I was stunned by the Serenity 7's.  I thought the TAD speakers were just as good.  Open baffle and servo is great way to design sota speakers, but it's not the only way. If this thread hadn't veered so quickly, it might have centered on whether good OB speakers are easier to design than good box speakers and why.  That might have been more informative.