Axiom Home Page Forums General Discussion Technical Questions Subwoofer Servo Technology

Axiom may ber aware of a engineer Brian Ding and his tiny startup company called Rythmik Audio out of Austin Texas. He markets a unique subwoofer technology called direct servo. Among the DIY community Rythmik seems to have an outstanding reputation. And although I'm far from an electrical engineer, after reviewing his web site rythmikaudio.com I'm thoroughly impressed by the simplicity and elegance of his design.

I am sure Axiom could license this technology for a song (Ian are you listening???).

It's somewhat of a alternate technology, I think it could provide some excellent synergy with the DSP approach used in the 500/600. In fact it seems more sophisticated that static DSP in that it provides real-time servo feeback and by all accounts provides serious distortion reduction and extended frequency response.

And no I don't have the slightest connection to Rythmik, monetary or otherwise.

Yeah, he only has 2 posts so far. One about an Outlaw, and the other this "plead" to Ian.

Welcome to the forum Peter. I am sure that Ian and Alan are all over the audio technology, and they probably hear of new technology before any of us do as well. Then they probably weed through the good and the bad, and design their own goods. But then again, I get no gain from Axiom (the company) monetary or otherwise...

It does look like this rythmik guy is on the avsforums, and there have been some good response to what he's doing. Like others said, I'm sure that the pros know what they are doing.

DIY bass trap I just finished. I'm getting to be really good with this audio stuff.

Wolf, are you catching large mouth or small mouth bass with that trap?

Sorry guys. I thought this was a technical forum - my mistake.

It is a technical forum, but again, look at it from our point of view. A new guy pops in, talks up a new type of technology that at least most of us have never heard of (thus the reason you posted, to share information, and thank you for that). Your tone and content of your message sounds like an advertisement, which is what this forum tries to steer away from. This isn't AVS. Good people over there, but a lot of bad apples as well.

Axiom forums have been known for being open and friendly, and when posts are made that seem to want to steer it down the dark path of some of the AVS forums, you will see some resistance. Also, in defense of the others. BrenR has a dry sense of humor (I like it). DrunkenWolf is new, sort of, around here, and he is just trying to add humor. It isn't a slam against you at all.

You will not find another audio (and visual for that matter) forum on the web with a stronger sense of community and light-hearted enjoyment for the A/V world than Axiom's. Give it a little time, and build up your reputation before coming across as someone scouring the web looking for forums to post a message that sounds like an "ad", and you will fit in just fine.

Great Post, Nick.

Peter, you are most welcome here, and I hope you've not been offended. Try to understand that every now and then we get new posters whose only aim is to hype a product or service.

Having just become acquainted with Rhythmik (I assume that's Brian using that screen name) in a subwoofer shootout thread over at AVS, and being being pleased, so far, with his posting style, giving you the benefit of the doubt, I'll assume you meant only to inform us of something new you find interesting and exciting. I hope you'll understand that it's not easy for us to be certain that is the case.

Regarding Bren, you'll find his sense of humor to be an acquired taste. However, once acquired, it can be a constant source of amusement (and sometimes, amazement ).

Alright, alright, I reread my post and I did sound like a some cheesy company rep masquerading as a spontaneous loyalist. But trust me, somebody like Rythmik probably can't afford ANY marketing and if he blows his fledgling reputation with sleazy posts he's permanently sunk.

Also about the licensing angle, I am totally disinterested other than I'd like to see more technically advanced Axiom products come to market, and hey, I thinks it's cool when the small entrepreneurial inventor makes good.

Anyhow.... I was hoping to find someone who actually knows something about physics and electrical engineering who could discuss why Axiom went DSP when low cost servo technology is available.


P.S. I've never seen the AVS forum - what's the deal with them?

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I'd like to see more technically advanced Axiom products come to market,

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Umm, the DSP onboard the new Axiom subs were Axiom designed and then programmed with months if not years of efforts by Jim, an Axiom tech guru whose programming expertise is obviously very good. Call me crazy but designing and programming computer chips is considered cutting edge technology and not expensive, if you have the time to do it (DSPs on modern receivers are virtually a couple of bucks per unit these days).

I watched Jim during this building process for the prototype EP600. He had dozens of sheets of programming code to work through, tweaking each individual Hz until the DSP made the driver work in producing an equal peak (flat response) across the sub range. This would have been followed by testing in the anechoic chambers followed by more tweaking. Since this specific code would ONLY work for a single speaker design (change the cabinet, change the acoustics), the same had to be done all over again for the EP600. Jim has probably coded near half of the Windows XP OS in his DSP programming of the EP subs.
The result?
The EP500 has less than a TWO DECIBEL variation from the average across the 20-95Hz spectrum!! This is phenomenal and better than the reproduction i've seen with parametric EQs and DEFINES the most accurate sound reproduction possible (a straight line frequency response)!!



Creating a speaker with a flat response is NOT an easy feat (if it were then everyone would have made one by now), if not impossible without advanced DSPs to control the output; so to say that Axiom DSP technology is not advanced, is somewhat off the mark, no?
Many audio components are simple things like copper wire and analog signals. Many more "technically advanced" (e.g. digital speakers which you plug into a wall) are not exactly audio bliss. Sticking a new fangled miniature plasma screen on the side of a speaker with touch screen controls for a whopping 8 band EQ to say it is more technically advanced does not make a good speaker.
Have a look at the extensive and advanced research that Axiom does in the course of creating and tweaking their speakers over the decades. The appreciation of this work comes from reading about it and seeing it first hand, something that many audiophiles never take the time to do.

Hello peterb,

There is nothing new about servo-feedback design in subwoofers and Axiom isn't interested in servo-feedback designs. These have been around for decades and used by such subwoofer brands as Velodyne, PSB and Paradigm in numerous models that deliver very good performance, better than would have been achieved without servo-feedback integration.

However, Axiom believes that our DSP design in the EP500 and EP600 subs is superior to the older servo designs in a number of important ways. Without going into a long dissertation, using a custom-written DSP algorithm that contains all of the traits of our particular dual-voice-coil driver, the enclosure, our amplifier and the expected performance goals results in an integrated system that delivers much more linear performance and optimal output well into the sub-sonic region.

Moreover, using a custom DSP algorithm means that the sub can never be overdriven or damaged. The algorithm was arrived at throught constant measurements and test of the driver, the amplifier and the enclosure, with any non-linearities (deviations from the desired frequency response) compensated with new instructions in the digital code.

Me thinks you take offense WAY too fast. What I meant was:
"I'd like to see more, technically advanced Axiom products like the 500/600 come to market..."

Also, I didn't say or even mean to imply that DSP was a simple or unsophisticated technology. However, servo feedback systems, because of their dynamic nature, offer capabilities that are beyond what's possible with a static DSP implementation. Not that this is always the best or most cost-effective design, but intrinsically it's more complex and adaptable.

And please don't take offense (I own several Axiom speakers)but... a flat FR to 20 Hz at only 90dB is very good, but given the current competition, far from earth shattering performance.

I agree that the 500 and 600 subwoofers put out by Axiom are really outstanding, and I have never heard one! These subwoofers have really gotten people to notice Axiom, even some people that don't care for Axiom speakers (with or without valid reason). Audio gurus from all sorts of magazines, design groups, and installers are praising the outstanding audio of the EP500 and EP600.

Peter, I think that you are reading too much into Chesseroo's post. He isn't coming down on you, just stating some facts, and asking you to consider them compared to your statements (like when he typed "No?"). It is just to spark conversation. Don't get discouraged or frustrated. Go ahead and keep posting your thoughts and even better some facts about the technology, then we can all speak to it with some technical insight.

I'm always interested in learning. I aspire to inclusiveness.

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I was hoping to find someone who actually knows something about physics and electrical engineering who could discuss why Axiom went DSP when low cost servo technology is available

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I think Alan answered this question above. Axiom - at its heart an R&D company - believes the DSP path offers superior performance.

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However, servo feedback systems, because of their dynamic nature, offer capabilities that are beyond what's possible with a static DSP implementation. Not that this is always the best or most cost-effective design, but intrinsically it's more complex and adaptable

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I'm going to suggest "debatable" here rather than "intrinsic". Your earlier comment about finding "somebody who actually knows something" leads me to think that your assertions about the "intrinsic" benefits of certain technologies may come from other sources. Care to cite them? "Technical" Forum and all that.

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a flat FR to 20 Hz at only 90dB is very good, but given the current competition, far from earth shattering performance

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Are you going to suggest the alternatives by name and cite the quantifiable data, or just leave this hanging out there? What's "better"? How do YOU KNOW it's "Better"? How much does "better" cost? How are we measuring "better" this week?

Look, I'm not trying to be a hard case here. I like fun new blinky stuff that plugs in as much as the next guy. You are advocating and defending technology that is "different" - not "new" - while dancing perilously close to "Axiom doesn't know what they're doing if they're not pursuing THIS".

I liked Alan's reply. And yes, I do get grumpy before lunch.

So cute the way y'all spring to defend Axiom's honor against any perceived slight. Touching really.

I love Axiom, I buy their products, I know the whole story about Floyd Toole, the NRC etc. But do they represent the last word in audio? Are all technical approaches other than theirs wrong, a priori? Give me a break.

A priori?
Interesting choice of words considering it was used in an incorrect context. A priori to what?
The sentence doesn't make any sense without a reference.
Neither does your argument about how Axiom should be pleading at the doorway of Rythmik Audio for their amazing, "new" technology.
I guess i'll just go back to defending my Tannoys...oh i mean my Monitor Audi...no no, my Axioms because that's where my heart and soul of speakers is at and i have nothing better to do.

Main Entry: a pri·o·ri
Pronunciation: "ä-prE-'or-E, "a-; "A-(")prI-'or-"I, -"prE-'or-E
Function: adjective
Etymology: Latin, literally, from the former
1 a : DEDUCTIVE b : relating to or derived by reasoning from self-evident propositions -- compare A POSTERIORI c : presupposed by experience
2 a : being without examination or analysis : PRESUMPTIVE b : formed or conceived beforehand

I know, let's have idiotic fights about everything!


Geez, people, Peter's just trying to make a suggestion.

Peter, everybody's just protecting the brand they love and our hosts.

Again, I hate everyone this week.

I would like to see some facts to back up the claims, that's all.

Peterb, you've been asked to provide technical details, like TomTuttle did a little bit ago.

As I've said a few times already too, you wanted to start a technical discussion, or so your post on 08/08/06 at 8:19am central time stated, yet you haven't provided any technical facts. PLEASE do, and I WANT to get a good discussion going here.

My request for technical data is not an insult to you, or some bash of the technology, so please stop taking it that way and just shoot some facts and data at us and we can get past this bickering.

That's okay, Ken. We hate you this week, too.

I read most of the thread at AVS, and actually spent a fair amount of time digesting the info at Rythmik. I thought the AVS thread was the usual train-wreck and that the Rythmik stuff was pretty compelling, in that "our products have cool technology - buy them" kind of way. Seriously, I can see that the theory behind active-servo subwoofer design is seductive. Heck, by the time I got done, I was ready to buy/build a sealed box sub just to see for myself (if I had the money, that is). I can see how a discussion of the various theories, philosophies and approaches to reproducing sonic and sub-sonic content could be interesting.

And I think the right forum for that is AVS. While there are several Axiom board regulars who are armed for the science involved, our hosts have already succinctly explained their philosophy and approach. I mean, why belabor it here? The phrase "asked and answered" comes to mind.

Those of you that are interested should check out the AVS thread and the Rythmikaudio site. Pretty cool stuff, most of which clearly dwells upon the scientific theories (which are admittedly beyond my level of expertise) rather than the demonstrable real-world impacts on my personal listening environment.

You academics go have a ball with this. I'm going to go enjoy some music instead.

Nicely done Tom.

Thanks, Dave. Have you started the Halloween installation yet?

What's the plan for this year?

For this year the plan is to hijack some Axiom threads

Seriously, not much this year other than some needed maintenance and replacing some of the lighting. Not much as October we are going to FL for 2 weeks. Maybe I'll have time to make another tombstone.

For 2007 I am hoping to add something new, but haven't determined exactly what- trying to brainstorm some great new ideas.

In the world of speakers, Axioms are sui generis. That tidbit of knowledge is not a priori, but rather a posteriori.

You need to add your old Tivo Avatar to the archive in the Water Cooler.

Hey, thanks for the plug, Tom! What a guy.

Yeah, Dave, post away. Here's the link.

Okay guys, I'm on it...

just as soon as I figure out what Peter is saying

Yeah, Dave, Peter(buko)is tossin' around some lawyer-like talk(although I'll raise his a posteriori with an ex post facto)for the simple fact that Axioms are in a class by themselves, as determined by experience, not speculation.

Now that's a post I can agree with!

The last time I heard "a priori" was in philosophy class in college. AFAIK, peterb used it correctly here. Too bad he didn't follow up his other assertions as well.

He and Stone__Man are right about the vigorous Axiom defenders, to a degree. As expected, there's a range of tact/diplomacy in our responses to a challenge, with people such as Jack and tomtuttle on one end of the spectrum and BrenR on the other. Wasn't it tom who said God loves diversity?

Well, I guess whether he was a troll or not, we circled the wagons and scared 'im away good, huh?!

This is my first post to this forum. Please be easy on me but I have to chime in here. I am in a debate with some gentlemen on the audio circle forum about the Rythmic sub. To me the Rythmic sub is hype. They claim to "achieve lower extension and flatter response in a small enclosure" - from the Rythmik website using their patented servo technology. For starters, servo tech has been around for years High Gain Servo™ Technology Patent by Velodyne in 1984 just to name one.

They claim their subs work in a 2 cubic foot enclosure to me this is not a small enclosure.

Here is the website… http://www.rythmikaudio.com/

I can see how the axiom sub using DSP is using new technology but the Rythimic sub uses old technology and claims it as their own. Or this is how I perceive it after reading their website.

I am of base here or am I on the right track?

Well let me add my voice to the chorus that Brian Ding is a terrific sub designer. While it's true that servo technology has been around for some time, Brian has spent six years tweaking and researching it in order to get better linearity, low distortion and deeper response than what one would normally have from a servo controlled sub. He has developed some propretary techniques to achieve these objectives which is why he suggests his technology DirectServo requires a special driver and a dedicated amp.

I've always had a keen appreciation for how a well designed sealed sub can perform and with that in mind I spent a week or so last summer conversing with him about the upcoming 15" version. He was very open about his ideas. From what I gather he started tweaking the servo sealed box 6 years ago with a 15" NCA driver. He preferred that driver because of its low inductance so that the zero phase crossover in the impedance curve was in the order of 150hz. Because that driver was expensive to make he later used a modified 12"TC Sounds driver which used a propretary short circuit ring in the servo mechanism to help achieve his design goals.

For the amp he likes using his own designed A370SE which is now shipped with a torrodial transformer, instead of the EI type. I don't know what else he has done to the amp except that it seems to match well with the enclosure and driver. The dedicated amp is critical to achieving low distortion levels in his subs. The extra SPL gain is mainly from high BL value and the larger enclosure.

While I do not suggest I know all the intricacies in his ideas or design, there is no doubt he has developed modifications which push the servo technology to the next level. It has been targeted at the DIY market but I believe its only a matter of time before he starts mass producing those subs. Judging by the many positive comments he has a strong following. It would be a mistake to dismiss the Rythmic subs as using old technology which he is calling his own.

I was afraid.

But that was actually quite civil, illuminating and interesting. Bravo!

Wow that was very interesting and enlightening! That was just the information I was looking for! 
Sounds like a good concept but with today’s crop of super woofers is the servo control really necessary?

Matt

Thanks Tom. I'm finding insomnia helps my posts.

If you are looking for a well priced sealed design, a good servo mechanism makes a big difference in performance. The Rythmic and Paradigm Servo are good examples and even the more expensive Velo DDs use a digital servo control. IF you don't mind doing some DIY stuff the Rythmic subs are pretty cheap for their quality and excellent servo technology. Servos add alot for not much extra cost.

I had an opportunity to listen to a pair of JL F113s "super subs" a couple of nights ago and they were very impressive, powerfully tight sealed subs with no servo. Instead they have 2500W amps and a massive 70lb driver but they retail for over US$3000 each.

>>Instead they have 2500W amps and a massive 70lb driver but they retail for over US$3000 each.>>