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The forum is kind of slow lately so I want to revisit a question I never got a good answer to. I'm not sure if the litigation between Velodyne and Paradigm has ever been discussed here. I've wondered if this is the reason Paradigm stopped using servos. Would Paradigm subwoofers work better if they employed servos?

Velodyne Acoustics, Inc. v. Paradigm Electronics, Inc., Case No. C-98-3553, (N.D. Cal. 1998).

This was a patent infringement litigation involving two U.S. patents owned by Velodyne for high-end loudspeakers. Mr. Aitken represented accused infringer Paradigm Electronics, Inc. and served as lead counsel. This matter was settled before the discovery phase was completed.
MajorJuggler had this to say about servos in the Paradigm Sub 1 and Sub 2 thread:

Originally Posted by MajorJuggler
I normally wouldn't jump into the middle of this, but my dissertation topic involves what would be analogous to a servo system, for underwater transducers, so I feel somewhat obligated to respond for the education of others here. I haven't worked with in-air acoustic systems, but I do understand the fundamental objectives and engineering tradeoffs involved with such systems.

The fundamental goals of an in-air servo system are typically to obtain a flatter frequency response, and to lower distortion. There are good and bad implementations of servo systems, just as there are good and bad implementations for everything else in a subwoofer design (not the least of which are the digital control systems, but I digress). It is incorrect to state that the purpose of a servo system is always to compensate for a poor acoustic design, and it is equally absurd to state that a good acoustic design and good control system are mutually exclusive. It can be very difficult to properly design a servo system, to the extent that it is common to only add a servo control to the flagship product line only after all other acoustical design tradeoffs have already been optimized.

There could be many reasons that Paradigm has opted to use open-loop DSP control rather than a closed-loop servo system. The difficulty of ensuring feedback loop stability while maintaining meaningful loop gain immediately comes to mind, as servo stability is particularly prone to higher order mechanical resonances.

One example of a subwoofer that is generally regarded as having both a good acoustic design and a good servo control system is the Velodyne DD-18. For its time, it had low distortion and flat frequency response, and arguably is still a very capable subwoofer, albeit not at the extremely low frequencies.


The only subs using servos I am aware of are Rythmik and Velodyne. Here is an old posting I found explaining the differences:

Originally Posted by Rythmik
I am not trying to shoot down any technology, but if one reads the patents of Velodyne (I have them because they are my prior art), it is not how the servo is applied. Very surprisingly, it is about 1) how the sensor is constructed so that it is air tight without pressure interference from the enclosure and 2) the location of the sensor on the cone. Each problem exposed the shortcoming of accelerometer based approach. And then, Velodyne adds 3) digital sampling to reduces the "hum" noise because the sensor signal is so weak that it needs high gain amplifier to make that signal useful (not covered by patent) And there are other issues with them such as 4) very poor tolerance to overloading so that it needs a limiter to protect it from catastrophic damage (inherited with all accelerometer-based approach). The root cause of the first problem is the sensor does not react to acceleration, instead, it reacts to pressure. It is made of a pressure sensitive material attached with a loading mass. The pressure transmitted by deformation of the sensor casing can caused so called distortion (not harmonic). That is what we call parasitic signals (the signal that we really don't want). The location of the sensor is important because it needs to sit on a structurally rigid part of the cone so that there is no cone breakup mode to affect sensor pick up breakup mode instead of cone acceleration.

Our sensing coil based approach is completely different. 1) we don't use secondary sensing. The velocity signal is picked up directly via BL*v. There is no secondary media. Coils is used in a lot of high fidelity music instrumentation is well proven to its sound quality. 2) the location of the sensing coil is co-located with driver coil. There is no cone breakup mode to worry about. There is no mechanical delay at all. 3) Our sensing signal is so large that it is in the 10 volts or higher range. No op-amp is needed and it can feed back to power amplifier directly. 15 ft distance between amplifier and driver is not even an issue. 4) The system is "unconditionally" stable. It is resilient to overload and that is why we don't put in limiter. I always compare this to hockey playing. Occasionally going out of board is ok as long as it does not destroy the system :)

Velodyne once sued Paradigm for patent infringement. I cannot see the reason.

Most patents are results of trial-and-error. Velodyne's patents are examples. Our patent is based on solid theoretical foundation that very few if any knew how to do it before me. I once talked to European engineers what I was working on. They asked me if I was sure it works because they cannot get it working. The system also gives us good sound without the compromise of limiter to clamp the output. That is why I really consider this is the best trade-off of both world. Imagine if we need to stop or slow down the game whenever a hockey player committing a foul, how many people would still want to watch them? Continuity is the key consideration here.

A lot of customers asked me why you wouldn't just use the driver from A and put together with amp from B to get a servo capable of producing 4000WRMS output. Sound quality is my primary consideration. There is no technological limitation on how much power one can apply to servo. However, so far I haven't heard a good high power one pleasing my ears. I am still looking. I have a customer bought 4 units of DS1500CI just to get sufficient output comparable to those 18" monsters with 2" excursion. But he still admits our sound is cleaner. There is only one way to get clean sound. A lot of the mentality on this forum is that if I can play 170db SPL, no one can beat me in sound quality at 100db. We all know that is flawed because distortion does not scale well. Sure a lot of people would completely dismiss the notion of distortion as they also claim distortion is not audible.

I tend to write a lot and hope I don't bore you guys.
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