The Rythmik-Ascend subs are getting good reviews, at least in part because of the servo.

Velodyne has been making servo subs for many years. Velodyne patented its servo in 1982.

Paradigm also has had its own servo in the Servo 15.

Is the anything new or special about the Ascend servo?

AFAIK servo's all hold down THD, typically at the expense of ultimate output.

If the designer of the Ascend servo has figured a way around this compromise, I would love to hear about it.

have not heard anything about it, i know velo also uses a "dual tandem" motor design... i think its a linear motor, not sure about that tho.

The later Velodyne's use a system similar to that used on JBL's differential drive. Like W15GTI. The Rhythmik's used to use a modified TC Sounds TC1000 platform. The Rhythmik's aren't as tightly regulated as the Velo's. There is some mention of this on Rhythmik's website. They don't use the really strict limiter's that Velodyne does so they will allow some more distortion at loud levels but they also should maintain their dynamics better. The Rhythmik's use a much different (simpler?)system that is not accelerometer based.

Look at Illka's testing of the 12" Rhythmik (a decent performance for a tiny 12") versus the 12" Velodyne he also tested. If you can assume that the 15" version adds about 3db across the board and that you can get a pair of the 15" Rhythmik's (another 6db) for about the same price or less than a comparable Velodyne (or Paradigm Servo 15) they look like a nice option. Not exactly home wreckers but probably quite capable and flexible.

I find it interesting that at least in the 12 inch version, the Ascend-Rythmik does not use any bracing in the box the company makes and sells for its subs.

Recently someone mentioned that the Velodyne DD series, at least the DD-18 has no bracing in the cabinet.

IIRC, folks were very surprised given the density and bracing of the cabinet for the J L Audio F 113.

here's some info from the site:

How is Direct Servo different?

Our philosophy is to make audio products as simple as they can be. Less is more. Our subwoofers put as little into the signal path as possible. This approach applies to our amplifiers, Direct Servo technology and drivers. Most servo subwoofers use an accelerometer, which is another mechanical system with its own limitations. Also extensive protection circuits are required, and these further degrade the signal. As a result, accelerometer based servos are not as accurate as Direct Servo. The superiority of Direct Servo is derived from its simplicity.

demo and more info at this link:

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

Besides the dual-opposed-coil motor, the Velo also comes with a built-in SMS-1. That's worth a little premium, I think.

The later Velodyne's use a system similar to that used on JBL's differential drive. Like W15GTI. The Rhythmik's used to use a modified TC Sounds TC1000 platform. The Rhythmik's aren't as tightly regulated as the Velo's. There is some mention of this on Rhythmik's website. They don't use the really strict limiter's that Velodyne does so they will allow some more distortion at loud levels but they also should maintain their dynamics better. The Rhythmik's use a much different (simpler?)system that is not accelerometer based.

Look at Illka's testing of the 12" Rhythmik (a decent performance for a tiny 12") versus the 12" Velodyne he also tested. If you can assume that the 15" version adds about 3db across the board and that you can get a pair of the 15" Rhythmik's (another 6db) for about the same price or less than a comparable Velodyne (or Paradigm Servo 15) they look like a nice option. Not exactly home wreckers but probably quite capable and flexible.

I get more DB's output from a Single 15inch Rythmik SE, then I did with my SVS PC12 Ultra. It also goes deeper. But again, I don't listen at reference levels. Adding the Second one evened out my FRQ response a bit. But was a tough situation already do to room constraints and placement options for me.

I would seriously recommend the 15 inch rythmiks in the same sentence with HSU, SVS etc etc, having owned quite of few of them, it puts out the cleanest bass I've heard.

And this is for pure HT/gaming in a 3500 cubic foot room.

I have the Rythmik Audio DS15 servo sub and the older V1 Paradigm Servo 15. Since both have 15" servo based drivers and 370-400 watt amps,it is a fiar comparison.

Both sound very very good. The main differences are that the Rythmik will play about louder (about 6db) and slightly deeper (f3 14Hz) than the Paradigm. However there is more distortion when playing the Rythmik at peak volume compared to the Paradigm. This is because the Rythmik doesn't limit the output based on distortion whereas the Paradigm does (very aggressively).

When played at similar volume levels, the Rythmik sounds at least as good as the Paradigm if not better and when asked to, can play louder and deeper, albeit with some additional distortion.

I have no doubt that the Ascend servo sub sounds just as good and is a nice alternative to other subs in it's price range.

Regards,

Dennis

Now that I think about it I'm sure that someone did a direct comparison of a 12" Rhythmik to a 12" Velodyne (DD?:confused:) and had a thread about it here a ways back.

one difference is amp power

If the designer of the Ascend servo has figured a way around this compromise, I would love to hear about it.
The person behind Rythmik is Brian Ding, and I believe he has a patent on his Direct Servo technology. There is a section dedicated to Rythmik subwoofers on the Ascend forum.
http://forum.ascendacoustics.com/forumdisplay.php?f=49

Brian posted that he will be away this week. If you ask him a question, he can get pretty technical if you want him too. There is also a lot of information at Rythmik's site as posted before.

I think he and DaveF really hit it off because they are both true engineers.

I know some are into ultimate output. These subs are not about that. I have heard a fair amount of subwoofers, and I would put the Rythmiks up against any of them when it comes to sound quality, and if you factor in price, I think they are a no brainer.

one difference is amp power

Rythmik answered this question in another thread, basically comparing a Bash amp (not sure what amp the Velo uses) to a class A/B amp and efficiency and power of a servo based sub. Dave F, said the Rythmik amp peaks at 700 watts.

The Rythmik-Ascend subs are getting good reviews, at least in part because of the servo.

Velodyne has been making servo subs for many years. Velodyne patented its servo in 1982.


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 :-)


Paradigm also has had its own servo in the Servo 15.


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


Is the anything new or special about the Ascend servo? AFAIK servo's all hold down THD, typically at the expense of ultimate output. If the designer of the Ascend servo has figured a way around this compromise, I would love to hear about it.


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.

Brian is it... Your explanations are never even in the realm of boring....

Always appreciate you stopping in here to lend us your incites and knowledge towards the servo design. You certainly know your stuff, and have certainly made quite a name for yourself with your products...

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 think Brian is referring to me! I do have 4 of the 15" Rythmik subs that I built, and I also built a dual 18" Maelstrom-x sealed sub. I have compared them using a lot of different music. The Rythmiks sound better, no doubt about it. A high quality bass note is hard to put into words, but it's like that judge and pornography--you'll know it when you hear it. A kick drum smacks your chest cleanly, and it's done, ready for the next note. No overhang, no muddiness, just a pure bass sound. It's not quite the same with the Maelstrom--just not as good. With room gain in my HT, the Rythmiks put out gobs of bass down to ~10Hz.

I think Brian is referring to me! I do have 4 of the 15" Rythmik subs that I built, and I also built a dual 18" Maelstrom-x sealed sub. I have compared them using a lot of different music. The Rythmiks sound better, no doubt about it. A high quality bass note is hard to put into words, but it's like that judge and pornography--you'll know it when you hear it. A kick drum smacks your chest cleanly, and it's done, ready for the next note. No overhang, no muddiness, just a pure bass sound. It's not quite the same with the Maelstrom--just not as good. With room gain in my HT, the Rythmiks put out gobs of bass down to ~10Hz.

Fatawan,

Thanks for chiming in here.

Brian