Subwoofer: Servo or not to Servo ....

[avnetguy]

I'm new to this technology of using a Accelerometer to control/limit a subwoofer's driver but it does sound like a good idea.

My question is, how well does it work and which ones would you recommend for home theater use?

Steve

 

[snickelfritz]

I've had a Paradigm Servo-15 for a few years.
The bass is really clean (no doubling at all), plays really loud, and will not overload, bottom-out or emit bad sound.
Theoretically, servo-subs will start to compress sooner than standard subs though, since the Servo circuit will not allow more than 10% distortion.
(If you have a very large space, you might want two subs to avoid compression at high levels.)

In my 13x17x8 living room, there is nothing about this sub that I dislike and I have never reached its limits.
It sounds very realistic with music and shakes the foundation convincingly with dinosaur foot-stomps.

 

[WmAx]

I'm new to this technology of using a Accelerometer to control/limit a subwoofer's driver but it does sound like a good idea.

My question is, how well does it work and which ones would you recommend for home theater use?

Steve

The effectiveness of the servo system is inversely proportional to the linearity of the transducer. The greater the linearity of the transducer motor, the less effect the servo system will have.

As for specific quantifications of commercial products using this technology: I am not aware of any quantitive tests regarding the matter[E.G.; analysis of performance of the subwoofer with and without the servo system engaged].

-Chris

 

[snickelfritz]

ie: the Servo checks the cone position 3500 times per second, then amplifier power is used to correct the frequency response, apply damping, and prevent the sub from exceeding 10% distortion or overloading.
It works.
The big trick is matching it with main speakers that are equally clean and well behaved in the crossover region.

 

[avnetguy]

So the technology does work ... well, at least for Paradigm.

Now would I be wrong in stating this would reduce (eliminate?) any damage to the sub in the event of clipping from overdriving?

Its disappointing that no quantitive tests have been done to compare the difference.

Steve

 

[snickelfritz]

Servo subs will not overload or damage themselves.
They simply stop getting louder when the threshold set by the servo is reached. (dynamic compression, which usually starts at the lowest frequencies)
This can be noticeable, but unless your main speakers are very sensitive and/or your main amplifier is very powerful, and you regularly play movies at extremely high levels, it's doubtful that you would ever notice this effect.

My B&W CDM 9NT speakers (90db/w/m) powered by an Adcom 5800 (24-26db/w) can reach very high SPL.
(theoretically 115db on peaks at 1m. I've never measured it, but it plays really friggin' loud).

The Servo-15 does not exhibit any noticeable compression or distortion in this system at maximum levels in a medium sized living room.
High level infrasonic bass, such as in "The Incredibles" DVD, always sounds absolutely effortless, natural and clean.
It's difficult to imagine how the performance of this sub could be meaningfully improved, aside from simply increasing the maximum output.

 

[Privateer]

I am not aware of any quantitive tests regarding the matter[E.G.; analysis of performance of the subwoofer with and without the servo system engaged].

Yes there is, on the velodyne DD series you have the option of turning the servo on or off.

 

[Privateer]

Servo controlled subs are superior but that is because they start with quality parts and then go from there. If you want a servo sub velodyne is the king of servo subs and subwoofers as a whole but you will have to demo some products and see which ones you like.

 

[WmAx]

Yes there is, on the velodyne DD series you have the option of turning the servo on or off.

Did you read the statement thoroughly before you answered? Just asking, because your reply does not fit very well with what was said in the post to which it replies.

WmAx wrote:

As for specific quantifications of commercial products using this technology: I am not aware of any quantitive tests regarding the matter[E.G.; analysis of performance of the subwoofer with and without the servo system engaged].

Specifically, I am not aware of 3rd party measurements/analysis of the servo system engaged vs. dis-engaged on a commercial product, so that the effectiveness is quantified, as the initial poster seemed to want, when he asked "how well does it work". While analysis of a particular product will not tell him the effectiveness, universally, it would give him some idea, at least in a limited scope of a particular commercial product.

Do you have a reference or link to such an analysis?

BTW, the more difference produced as a result of the servo system = the lower linearity the motor on the transducer. The servo's sole job is to correct driver error(s) due to non-linear behavior(s).

-Chris

 

[Privateer]

Do you have a reference or link to such an analysis?

Read through this, I do not know how accurate it is.
http://206.225.87.49/volume_10_4/velodyne-dd-18-subwoofer-12-2003-part-1.html

 

[MACCA350]

Definatly go for servo if you can. I upgraded to the Velo DD15 and once you've heard clean bass you'll understand why I'm watching all my dvd's again. There is so much detail that is lost on a less controlled sub.

Not just that but my previous sub(velo ct100e) reached to 28hz whereas the DD15 reaches below 15hz, and I've now found so many movie tracks go this low. I rewatched Alien Vs Preditor and in the scene where the ship passes above one of the people on its approach to the site, I previously heard a low hum as it passes over(I assumed it was a quiet ship). When I watched it with the DD15, Holy **** there is bass allright so loud and low it nearly rattled the door off its hinges and ripped the plaster off the walls

 

[WmAx]

Read through this, I do not know how accurate it is.
http://206.225.87.49/volume_10_4/velodyne-dd-18-subwoofer-12-2003-part-1.html

Thank you for the link. The analyzed subwoofer in the link has a very well designed motor, and the servo feedback system is more of a marketing feature than a useful feature on this particular subwoofer[due to the very linear/high quality transducer used]. However, if one uses the woofer at it's maximum mechanical excursion/incursion[something that should be rarely encountered], the servo system would do considerably more than is demonstrated in the measurements.

-Chris

 

[avnetguy]

Read through this, I do not know how accurate it is.
http://206.225.87.49/volume_10_4/velodyne-dd-18-subwoofer-12-2003-part-1.html

Thanks Privateer, that was a good read.
That's quite the system they have there, overkill for my own use really but I wouldn't mind having it.

While the results for the servo control didn't seem that impressive with small reductions in THD under test conditions, I'd like to see how it would deal with an overdriven signal.

Steve

 

[Jase]

Yes there is, on the velodyne DD series you have the option of turning the servo on or off.

Nope. You can adjust the Servo setting from 1 to 8 (8 giving the tightest bass) but you can't turn it off completely.

 

[MACCA350]

here is some more info on the DD series(DD12 review), it explaines some of the technical side of things.

http://www.velodyne.com/velodyne/news/review_files/DD-12 Hi-Fi Magazine_small.pdf