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Thread: Rythmik Audio 18s

  1. #31
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    Default Re: Rythmik Audio 18s

    Quote Originally Posted by curtis View Post
    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.
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    Good Sound To You!

    David Fabrikant
    www.ascendacoustics.com

  2. #32
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    Default Re: Rythmik Audio 18s

    I have had 3 servo subs designed by my friend Arnie Nudell, who I believe is the inventor of the servo subwoofer. Since he retired I can't afford to buy his stuff. I was going to go with dual Rythmics but decided on a design without forward facing drivers because of my infamous terriers. When the day comes, I will be buying a pair of Rythmics.
    Here is an article about Arnie and page 2 covers the Servo Sub.
    http://www.stereophile.com/content/a...0M11R5wcT0P.97

    Having Dave chime in on the forum is special and unique....Thank's

  3. #33
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    Default Re: Rythmik Audio 18s

    Quote Originally Posted by taigovinda View Post
    I have a 3-yr-old so drawn to down-firing. Is DIY (or Salk/Rythmik) the only option for down-firing right now? I was able to access an a D15SE link on Ascend via google search, but couldn't get there from within the Ascend site and it seems like it's maybe not part of the current offering.

    My room is about 8000 sq ft and I have an Outlaw LMF-1+ that doubles as end table, will probably get rid of when upgrading to Rythmik... what size of Rythmik would be appropriate for this room? I was told at one point that the best bet is two vented high-powered 15's... that the quality difference from sealed to vented Rythmik is not that much anymore and vented just has higher output. I would like to be able to use the sub(s) as end tables or coffee tables ideally; not sure from a cost/WAF/sound quality factor whether a center-of-room coffee table sub (maybe 2x12 or 2x15) would be better or maybe one on each sidewall - one of the two could be an end table. Or if the 18 comes out before I jump in, maybe just one that sits where my current one is... Also not sure if these big subs - especially when down-firing - can be held to the right height dimension.

    A lot in there - any input appreciated!

    Tai
    I am sorry Tai but the Rythmik D15 is no longer available. We have one here in the shop that I can offer to you, but we no longer have the appropriate packaging for shipping so you would have to arrange for a local pickup (if you are near our office)
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    Good Sound To You!

    David Fabrikant
    www.ascendacoustics.com

  4. #34
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    Default Re: Rythmik Audio 18s

    Both HSU and Outlaw have affordable down firing subwoofers. They are cheap enough to get a pair.
    I use a pair of outlaw 12" now and I am satisfied...I'll give them a B grade. Servo is tighter.

    B.

  5. #35
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    Default Re: Rythmik Audio 18s

    Quote Originally Posted by N Boros View Post
    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)?
    No - Servo is not about EQ in the conventional sense. Servo is about controlling the movement of the woofer. Generally speaking, it doesn't boost or cut frequencies.

    Think about it this way - we have a B12 bomber that is about to drop a bomb and fire a guided missile. Both of these are aimed at hitting a specific target. For clarity, that target is the frequency the woofer is supposed to reproduce and the projectile is the woofer cone.

    With a bomb, all the calculations are made in advance and once the aircraft releases the bomb - all we can do is cross our fingers that it hits the target. If the casing of the bomb has a dent on it, or if a big gust of wind comes, for many different reasons - that bomb might not hit the target.

    With a guided missile (a servo system) - the missile itself is constantly relaying feedback to the propulsion system (the amplifier) so that no matter what variables might come up - it will hit its target every time (woofer precisely reproduces the signal).

    In Brian's explanation, imagine adding another woofer into the box. This woofer will control the movement of the other woofer due to pressure. Nothing can be done about that by conventional means. In a subwoofer box, there is tremendous pressure - that pressure acts like another woofer and fights against the woofer.

    With a servo controlled woofer, the movement of the woofer by those external forces (or any other forces) will be compensated for by sending a signal to the woofer to oppose those forces. It is important to keep in mind that a woofer in itself is a voltage source, push that woofer in and out with your hand and it will generate a current. Try it yourself, grab a flashlight bulb, connect it to the positive and negative of the woofer inputs and simply push that woofer cone back and forth and watch the light bulb. The speed and how far you push down on the woofer will directly affect the light given off. It is from this information (the feedback from the woofer movement) that Brian's works his match so that the woofer is properly tracking the signal, regardless of frequency.
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    Good Sound To You!

    David Fabrikant
    www.ascendacoustics.com

  6. #36
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    Default Re: Rythmik Audio 18s

    Quote Originally Posted by taigovinda View Post
    I have a 3-yr-old so drawn to down-firing.
    Tai,

    I'm a little confused by why you prefer a down-firing subwoofer. From what I understand any bass coming out of just about any subwoofer should be omnidirectional, which means that it shouldn't sound different if it is down-firing or not (unless you are crossing it over very high). I think that the orientation of the woofer is more of a design choice related possibly most to aesthetics than performance.

    If you prefer a down facing driver so that the child doesn't possibly play with the woofer, then that does make sense. But, I can say that I have a 2 year old and 5 year old child and have had bookshelf speakers on stands for the entire time. My wife was really concerned about the speakers tipping over on them when they were first born, but it really isn't that big of an issue. We watched them closely at first making sure they know not to mess with them, and they quickly learned. It really isn't an issue now. I'm glad now that I didn't choose my speakers based on being able to wall mount them, just because I was worried about them tipping over on the kids.
    Last edited by N Boros; 10-11-2016 at 09:40 AM.

  7. #37
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    Default Re: Rythmik Audio 18s

    Dave, Curtis and Brian,

    This discussion about how the servo technology in the Rythmik subwoofers work has been very helpful. I have a much better understanding now. I think that comparing what most other subwoofers do with simple DSP cannot be compared at all to what Rythmik is doing with the servo technology, as you have said. This would be like comparing the the old Ford Mustang from the late 60's to early 70's with the new Mustangs from 2004 until now. Starting in 2004 Ford decided to go back to the body style that so many loved in the muscle car era. During those early years the body styles were quite close. In both cars you could get the option of likely the Ford 302 engine, either an automatic or manual transmission and both were rear wheel drive. But, the similarities ended there. It isn't even a contest comparing the performance between the two cars. Fuel injection vs. carburetor in terms of performance and fuel economy, computer for engine and transmission vs. well... no computer, handling abilities vs. ability to go fast as long as it is in a straight line, Antilock 4 wheel disc brakes vs. maybe disc brakes on the front, bluetooth GPS integrated into a nice stereo head unit vs. AM/FM and maybe a clock, etc. If your only concern is the look of these two cars and going fast in a straight line then either would do that just fine, but if you are looking for performance past that then the two are quite different.


    I used to be into restoring cars in improving their performance of them, but gave that up about 7 or 8 years ago. My old pickup truck that I was driving while restoring and was my only vehicle to get back and forth to work kept breaking down at very incontinent times and finally I had enough. If I was choosing which Mustang I would restore while driving, I would definitely choose the old classic one. The new one is far too complicated to work on for many things. But, if I had $30,000 to $40,000 and really liked the body style of that particular Mustang, I would definitely just get a new one. I think this is really similar to the DIY subwoofer community. I think if I spent some time and wanted to make a hobby out of it, I could put together a nice DIY subwoofer using DSP technology and it would sound pretty good after all that time and effort. Honestly though I am to the point where I would rather spend the extra money and not have to worry about fixing any quirks and troubleshooting things when I just want to sit down and listen to some music or enjoy a movie. Not only will the extra money buy me this ease of use where things should just work most of the time, but I think that if I go with a Rythmik I will be getting a big difference in performance as well.
    Last edited by N Boros; 10-11-2016 at 10:31 AM.

  8. #38
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    Default Re: Rythmik Audio 18s

    Quote Originally Posted by N Boros View Post
    Tai,

    I'm a little confused by why you prefer a down-firing subwoofer. From what I understand any bass coming out of just about any subwoofer should be omnidirectional, which means that it shouldn't sound different if it is down-firing or not (unless you are crossing it over very high). I think that the orientation of the woofer is more of a design choice related possibly most to aesthetics than performance.
    Downfiring woofers have gravity acting on their forward/back motion. This is just another force that creates inaccuracies in the final signal. In front firing woofers, gravity is acting perpendicular to the woofer motion and does not effect woofer travel differently across the woofer's motion. In downfiring systems, it does. The pressure inside the box works against the cone as mentioned previously by Rythmik and Dave, but now you're adding complementary force to the woofer as it pushes forward, and impeding the motion as it draws back. This means you have to correct for more forces through servo or EQ.

    Since we're on the topic, I'm not sure if a downfiring sub gives an advantage by using the floor as a re-radiating area, or by using the short distance between the cone and the floor as a way to increase air velocity of the wave as it leaves the woofer? This is what some speakers do that are vented on the under-side of the speaker, such as Zu's speakers. It makes sense to me, but I'm not sure how the physics of it actually end up in the real world.
    -Alex
    PS4/Nvidia Shield --> Emotiva XMC-1 --> Emotiva XPA-5 --> Ascend Acoustics Sierra Towers and Horizon Center w/ RAAL tweeters (L/C/R), HTM-200 SE (Surrounds), 2x Rythmik F12 subwoofers

  9. #39
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    Default Re: Rythmik Audio 18s

    N Boros, Alex,

    Yes, consensus from what I've read in various places is that the two form factors are equivalent in sound or maybe side-firing is a bit better. My concern is indeed that my son likes to climb on my current sub and smash toys against it; also the look of down-firing could appear more like an end table and less like audio equipment, even by purchasing a stock one and adding veneer. The fact that the down-firing is not readily available does change things for me - guess I'll have to either train my kid or else pay about 2x.

    For an 8000 sq ft room, would F15HP x 2 (non-vented) be right? In terms of output levels, I don't have a sense of how it would compare to what I have currently, the one vented Outlaw... or how it would compare to just one F15HP. I've read somewhere that output gain from adding identical subs is a lot less than going up a size, but I'm not sure that when the 18 does come out it would be the right form factor for me trying to be at end table height. The room is 33 x 15 x 16 (high point of sloped ceiling), the sub(s) would go against the side wall(s) close to halfway back in the room.

    Thanks.
    Tai

  10. #40
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    Default Re: Rythmik Audio 18s

    Quote Originally Posted by taigovinda View Post
    N Boros, Alex,

    Yes, consensus from what I've read in various places is that the two form factors are equivalent in sound or maybe side-firing is a bit better. My concern is indeed that my son likes to climb on my current sub and smash toys against it; also the look of down-firing could appear more like an end table and less like audio equipment, even by purchasing a stock one and adding veneer. The fact that the down-firing is not readily available does change things for me - guess I'll have to either train my kid or else pay about 2x.

    For an 8000 sq ft room, would F15HP x 2 (non-vented) be right? In terms of output levels, I don't have a sense of how it would compare to what I have currently, the one vented Outlaw... or how it would compare to just one F15HP. I've read somewhere that output gain from adding identical subs is a lot less than going up a size, but I'm not sure that when the 18 does come out it would be the right form factor for me trying to be at end table height. The room is 33 x 15 x 16 (high point of sloped ceiling), the sub(s) would go against the side wall(s) close to halfway back in the room.

    Thanks.
    Tai
    Indeed, totally support your decision based on your kid and your room, no problems there, just discussing the physics of it.

    FWIW, I own two F12's in a pretty big open room and it gives SCARY amounts of bass when called for. I run them at about 1/3rd volume each, normally. I think that two F15HP's would totally rock your world.

    Finally, the grilles that come with Rythmik subs are pretty beefy frames, so even if your kid is pawing at it, it'll give them a good amount of protection. SVS also has some models that have metal grilles on them for more protection, but they're small, overpriced, and not servo subs.
    -Alex
    PS4/Nvidia Shield --> Emotiva XMC-1 --> Emotiva XPA-5 --> Ascend Acoustics Sierra Towers and Horizon Center w/ RAAL tweeters (L/C/R), HTM-200 SE (Surrounds), 2x Rythmik F12 subwoofers

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