Rythmik Audio 18s

[davef]

The new SVS 16'ers have a 1500W amp. I wonder how this power will translate into sound compared to Rythmik? the sealed box model is only 19.5" wide... DSP vs. accelerometer? I wish I had a bunch of new subs in my room to play with. Affordable high value audio is getting better every day.

DSP is not comparable to servo. DSP is one method (actually, a lesser expensive method these days) for equalizing / contouring the subwoofer's response as opposed to equalizing by analog means. It means the LFE signal that is being sent to the sub is once again converted to digital - then various filters are applied to the digital signal, and then it is once again converted to analog so it can be amplified and then sent to the woofer.

Regardless of how good the DAC's are - each time an analog signal is converted to digital and then back again, information is lost.

Servo is a real time solution whereby the woofer sends a continuous signal back to the amplifier, so that the amplifier makes sure the woofer is properly tracking the signal being sent to it.

DSP does not have any effect on overall sound quality other than adding additional features and a simpler way of implementing eq. In fact, because of the additional A/D D/A conversions, it has a negative effect on the purity of the original signal being sent. These days, there are way to many A/D D/A conversions taking place in the audio chain. DSP in a sub would be more beneficial if the LFE output itself were digital.

I'll take servo any day of the week when it comes to sound quality in a subwoofer.

[billy p]

The most important aspect of the sub IMO is the driver itself....efficiency, inductance...motor strength...distortion.... will shape or identify the SQ...long before a servo or DSP is put in chain.

I suspect even you Dave would be impressed with the TSAD specs at DB in the Funk subs...I'm using no eq....and its awesome...its basically an extension of the Towers only better...

[sludgeogre]

The new SVS 16'ers have a 1500W amp. I wonder how this power will translate into sound compared to Rythmik? the sealed box model is only 19.5" wide... DSP vs. accelerometer? I wish I had a bunch of new subs in my room to play with. Affordable high value audio is getting better every day.

A servo sub is managing the backwave radiation inside the box to heavily reduce it, other subs can't do that, or just have overbuilt boxes to manage it. It means that the signal the servo sub produces will be more accurate. Normal subs need a bigger amp to deal with the deleterious effects that they can't manage. Also, Rythmik subs are direct servo, so they don't use an accelerometer, they use a sensing coil that is in the same magnet gap as the voice coil. The sensing coil sends feedback to the amp and corrects the signal being sent to the woofer. The result is a much more accurate signal.

This is why I don't understand why more companies don't implement a direct servo design. It must just be difficult to do correctly, or they just want to market giant amps and boxes, because people like big amps and big boxes, especially ones that shake a lot. It's probably more of the latter and some of the former. I mean my Dad put floor shakers in his theater as well as having a big rumbly sub. It was too much for me. I prefer accuracy and gut punching depths of rock solid sub 20 Hz bass that Rythmik subs provide. When I first heard that kind of bass from my dual F12's, it scared the hell out of me and I was immediately thrilled as my heart instantly sank because my neighbors must have been freaked out. I was immediately addicted.

DSP is not comparable to servo. DSP is one method (actually, a lesser expensive method these days) for equalizing / contouring the subwoofer's response as opposed to equalizing by analog means. It means the LFE signal that is being sent to the sub is once again converted to digital - then various filters are applied to the digital signal, and then it is once again converted to analog so it can be amplified and then sent to the woofer.

Regardless of how good the DAC's are - each time an analog signal is converted to digital and then back again, information is lost.

Servo is a real time solution whereby the woofer sends a continuous signal back to the amplifier, so that the amplifier makes sure the woofer is properly tracking the signal being sent to it.

DSP does not have any effect on overall sound quality other than adding additional features and a simpler way of implementing eq. In fact, because of the additional A/D D/A conversions, it has a negative effect on the purity of the original signal being sent. These days, there are way to many A/D D/A conversions taking place in the audio chain. DSP in a sub would be more beneficial if the LFE output itself were digital.

I'll take servo any day of the week when it comes to sound quality in a subwoofer.

I love this post. This is true audiophile engineering here. Keep the signal pure and do as much as you can to keep it that way at every step. This is why I love my Schiit Bifrost Multibit so much. It stays out of the way of the music. It's so accurate, I constantly notice new things. I'm listening to Wedding Nails by Porcupine Tree again and I never really noticed how much ambient keyboard there is in the background before. You can't discover new and incredible details in music you've listened to for years on a system that is constantly screwing with the signal you send it.

[curtis]

I love this post. This is true audiophile engineering here. Keep the signal pure and do as much as you can to keep it that way at every step.

I believe this is why Dave spends so much time on getting the drivers in his speakers "right". Doing this means there is less interference needed by the crossover.

[billy p]

I believe this is why Dave spends so much time on getting the drivers in his speakers "right". Doing this means there is less interference needed by the crossover.

Having control of the driver design from the ground up is what makes Rythmik, Funk, JTR, Seaton and Svs for that matter so unique. Dave relationship with his OEM is likely unparalleled...geting the right driver for the given task helps eliminate some of the added processing to reach the desired results.

Most of the DIY community don't have this available to them and why off the shelf parts need plenty of tweaking but if done right can be made to sound just as good.

Not trying to play devil's advocate here but I can guarantee you any sub from the Seaton, JTR or Funk will sound great with or without a servo.... JMO.

[RythmikAudio]

If you imagine all drivers are same out of the factory, then the benefits of servo is just improving distortion and make the bass sound less boxy. Let us assume that for a moment. The Achilles heel in stoping boxy sound is the cone itself. We all build thick wall enclosure to stop the internal boxy sound from coming out through walls. But how about the cone? Does the boxy internal sound just magically avoid the cone? So after we build a thick wall enclosure, all the boxy sound now comes out from the cone. Servo reduces that boxy sound coming through the cone by up to 10x in energy becasue servo fight against any unintentional cone movement that is not in the signal source. To measure that you need to place another driver in the back of the enclsoure to emulate a source of boxy sound. Then you measure how much the cone moves under this pressure. One measurement for servo and one measurement for nonservo and you get the improvement. That is how much clarity servo can improve.

Now if you look at another real world issue called variation which servo also helps. Variation consists of aging, unit to unit variation and batch to batch variation. There is an JL audio discussion on the version of firmware in those subs even for the same model. Why did they do that? It is batch to batch variation. It is like in a factory that you recalibrate your tool once in a while. Servo makes that easy because it is a close loop system that all variations that I have named above are reduced by the servo feedback.

[billy p]

Thanks for explaining thing in layman terms. Rythmik was on my short list...hence my curiosity when I heard about the upcoming 18" designs.

Unfortunately...a single sealed 18"...was not in the plan at this time....so I had to focus on those mfg who offer the compact design I need for my current needs.

I'd like to experience a Rythmik product one day...in hindsight...I could have waited I suppose, given the current delays, not sure on when the new 18" will be coming out.

Unfortunately, most of the local folks I know are into DIY designs.... thankfully...I have not gone down that rabbit hole, nor do I have any future plans in doing so.

[N Boros]

DSP is not comparable to servo. DSP is one method (actually, a lesser expensive method these days) for equalizing / contouring the subwoofer's response as opposed to equalizing by analog means. It means the LFE signal that is being sent to the sub is once again converted to digital - then various filters are applied to the digital signal, and then it is once again converted to analog so it can be amplified and then sent to the woofer.

Regardless of how good the DAC's are - each time an analog signal is converted to digital and then back again, information is lost.

Servo is a real time solution whereby the woofer sends a continuous signal back to the amplifier, so that the amplifier makes sure the woofer is properly tracking the signal being sent to it.

DSP does not have any effect on overall sound quality other than adding additional features and a simpler way of implementing eq. In fact, because of the additional A/D D/A conversions, it has a negative effect on the purity of the original signal being sent. These days, there are way to many A/D D/A conversions taking place in the audio chain. DSP in a sub would be more beneficial if the LFE output itself were digital.

I'll take servo any day of the week when it comes to sound quality in a subwoofer.

That is a really helpful explanaintion of the differences! This is really simple to understand as well. I do have a follow up question though. Filtering the analog signal in real time sounds kind of tricky. Is it kind of like just a sophisticated graphic equalizer boosting or cutting frequencies that differ from when the true signal is supposed to be (where this difference is measured in the accelerometer)?

[curtis]

That is a really helpful explanaintion of the differences! This is really simple to understand as well. I do have a follow up question though. Filtering the analog signal in real time sounds kind of tricky. Is it kind of like just a sophisticated graphic equalizer boosting or cutting frequencies that differ from when the true signal is supposed to be (where this difference is measured in the accelerometer)?

I can't explain it like Dave, but servo control is not a filter in the same sense as an EQ. It tracks the position of the woofer vs the output of the amplifier. It corrects in real time rather than preset filters....so it can handle anomalies such as the environment, memory, etc. On top of what the servo does, you can apply traditional EQ to it...as evidence of the parametric EQ on the amp.

and as sludge said, the Rythmiks use a sensing coil, not an accelerometer.

[davef]

I can't explain it like Dave, but servo control is not a filter in the same sense as an EQ. It tracks the position of the woofer vs the output of the amplifier. It corrects in real time rather than preset filters....so it can handle anomalies such as the environment, memory, etc. On top of what the servo does, you can apply traditional EQ to it...as evidence of the parametric EQ on the amp.

and as sludge said, the Rythmiks use a sensing coil, not an accelerometer.

Curtis is correct. By design, Rythmik woofers have an additional specialized coil in the motor assembly. This coil generates voltage due to its movement within the magnetic gap of the woofer (which is in unison with the cone itself). From this voltage source (which is fed back to the plate amp) - acceleration and woofer position can be determined and instantly compensated for in real time.

There are a few reasons why you don't see many manufacturers going this route:

1. It is very complex. You are not going to see this from other ID manufacturers or in the DIY crowd as it really does take a highly educated and experienced engineer to properly design. This is not something that can be modeled by software and it throws typical woofer design (which rely on Thiele Small parameters) into the garbage. With Servo, T/S params are practically meaningless as they are compensated for by the servo functionality. This is what Brian mentions in his post - T/S params for any woofer will change over time as the compliance of the suspension system changes.

2. Rythmik's method of servo is protected by patent. The other method of servo is by use of accelerometer mounted to the moving mass (typically on the cone itself or the former). This is patented by Velodyne.

One of the reasons, amongst many, that I am so fond of Rythmik's subs is that I have a lot of experience with servo and its many benefits. I was privileged to be an engineer for a company that was at the forefront of subwoofer design, this was back in the late 80's early 90's when subs were just starting to become mainstream. Back then we had only one real competitor - and that just happened to be Velodyne. I spent a lot of time with the late Dr. Lester Field, a part owner of the company I worked for and a brilliant PHD'd engineer. He spent a lot of time measuring and evaluating Velodyne subs and I was there to assist him. We blew up a lot of amps back in those days (and a few $4k B&K mic capsules), but it is a very fond memory for me as Doc (as I liked to call him) was one of my major influences, a true mentor.

More importantly, even way back then - we realized the rather dramatic improvements servo brought to subwoofers. I assisted Doc in his evaluation of developing our own method of servo, but sadly, it never came to fruition due to his passing.

A decade later, as we (Ascend) started to develop our own line of subwoofers - I was introduced to a little known DIY company called Rythmik. Brian and I had many discussions back then and I knew he was the real deal, exceeding my own knowledge of subwoofer design (which was extensive). After he sent me a fully assembled F12 - (all while I continually evaluated many ID offerings such as HSU and SVS) - I was both disappointed and hooked. Disappointed because I knew right then that I could not outdo this design in terms of sound quality (and sound quality over quantity was my goal) yet at the same time instantly hooked because this sub measured better and sounded better than anything else before it. I had data stored from close to a hundred different subwoofers from so many years of work in this field. In fact, it was the only ID sub I had measured that actually met its published specifications...

I instantly scrapped nearly two years of work on our subwoofer line - instead choosing to focus on assisting Brian in bringing these incredible servo subs to market.