Descent i and Depthi...Are they really servo controlled?

I am thinking about a sub to go with my new Ethos. I suppose there is a certain synergy to stay with ML. I see they advertise on the now discontinued Descent i and Depth I that they are "servo controlled". There is a lot of marketing that claim "servo control". To me, true servo control means the cone motion of at least one of the sub cones is monitored via an accelerometer and the signal is fed back and compared to the input signal, with an error amplifier adjusting the sub amplifier to minimize the error. Anybody know if the ML subs really do use that technique?

Thanks,

J. Tucker

Here's a link to the info you're after. It looks like the Descent i is a true servo controlled sub.

http://www.martinlogan.com/products/descenti#servo

"Triple-Servo Correction System

A highly sophisticated triple-servo control system for each driver compares input to output and applies automatic electronic correction for any deviation from the original signal. These advanced servos combine with the drivers' inherent linearity and their BalancedForce™ reaction-canceling alignment to yield the cleanest, most accurate bass imaginable, exhibiting absolute minimum distortion."

Why not just listen to the subs rather than worrying about the technology or the design execution contained within?

"Triple-Servo Correction System

A highly sophisticated triple-servo control system for each driver compares input to output and applies automatic electronic correction for any deviation from the original signal. These advanced servos combine with the drivers' inherent linearity and their BalancedForce™ reaction-canceling alignment to yield the cleanest, most accurate bass imaginable, exhibiting absolute minimum distortion."

That is what I would consider "marketing"...not even the slightest hint of technical detail. And yes, I am technologically obsessed. Just can't help it.

Well, all of that aside, the Descent I has more than proven itself as a very capable subwoofer. I have not heard a single disparaging word in the time I've been on this site.

I think the Descent is one of the greatest speakers made by Martin Logan. 3 10" woofers is about the same area of an 18" woofer, but the Descent avoids the problems caused by vibrating the cabinet and resonance. I wish it was continued in the current lineup, perhaps using 3 18" woofers.

Duke said:

I think the Descent is one of the greatest speakers made by Martin Logan. 3 10" woofers is about the same area of an 18" woofer, but the Descent avoids the problems caused by vibrating the cabinet and resonance. I wish it was continued in the current lineup, perhaps using 3 18" woofers.

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while 3x18inch in a star configuration would avoid cabinet issues, the problem with 18inch woofers is that it is too big to be properly controlled for high end audio creating serious distortions. hence current subs use multitude of smaller woofers for a better effect.

Pener said:

while 3x18inch in a star configuration would avoid cabinet issues, the problem with 18inch woofers is that it is too big to be properly controlled for high end audio creating serious distortions.

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I'm afraid that's one of those audiophile myths. A well-designed i.e. properly controlled large woofer, utilized within its intended passband, will produce less distortion than a similar smaller driver, not more. For any given volume, the larger driver is loafing along vs. its smaller brethren.

There are plenty of driver distortion measurements which demonstrate this.

amen to RUR's comments. One of the great distortion reducing design elements of a stat is a simple one: Large surface area. A speaker's distortion climbs with excursion. Since our smallest stat is huge as compared to a small midrange and a tweeter the result is they measure much lower in distortion than most drivers out there. Extending that thought, when we developed the Dynamo 1500, we did smaller woofer, big amp packages but could not reach the SPL/distortion targets. We went to a 15 even though that runs counter to the market hype of "smaller, but faster" woofer myths. Bass is slow folks, rise time is not much a challenge to a good amp/cabinet/woofer design. The 15 may not appeal to the marketing folks, but the measurements spoke. Audioholics, which do measure products, gave it the large subwoofer of the year award.

Peter Soderberg said:

Bass is slow folks, rise time is not much a challenge to a good amp/cabinet/woofer design. The 15 may not appeal to the marketing folks, but the measurements spoke.

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Struth.

Hey Peter, will you be shepherding the Neoliths at the upcoming Newport show? Can't wait to hear 'em.

yup, i will be there although have to leave Sunday to go yet another show(not an audio show). Mike Ware will be running the room. the Neolith's did great at Axpona last weekend with Dennis doing the sheperding.