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Rythmik L12 Subwoofer Review

Hidde

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I gathered from his description that voltage feedback from the small transducer coil was the primary input to the servo control. So, no, this is not a transconductance amplifier.

You seem to be interested in redesigning his scheme to what it could be.....I'm just relating to you what it IS. If you have some suggestions to improve his product, I suggest to contact Brian Ding directly.

Dave.
I think he uses the signal that is generated by the woofer. It definitely works, whether it's worth all the effort for the amount of gains that you get is arguable. Motional feedback after all is SIGNIFICANTLY more difficult to design than the "normal" kind of subwoofers.

I'm very interested in the design of MFB subwoofers. I don't really aim for redesigning his scheme. I highly prefer Grimm Audio's approach (I also think their subwoofer is the best money can buy at the moment, regardless of price). Their design methods are published on the designers website which can be found here: https://www.rmsacoustics.nl/audiodesign.html in case you or someone else is interested.

Rob, the designer, is also somewhat active on the dutch forum MFBlabs.nl. Though there hasn't been an update in a while.
 

DonH56

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I completely disagree. I own a Rythmik L12 for my bedroom system. And I own 2 of the same DIY 18" Sealed Dayton Ultimax's powered by an iNuke6000 for my large HT.

The 18" Ultimax is in a different league, especially for high SPL listening. It easily competes with the likes of the SVS SB-16 and Rythmik F18. Now in my relatively small bedroom it would be way overkill and the Rythmik L12 is a wonderful sub to listen to for that space. In terms of bass quality, I prefer the Ultimax's in my large mid-field setup over my Rythmik in a small near-field setup. And the Dayton has the output equivalent of 8 Rythmik L12's. For $1400 to build two of them, there is no other product that can come close to the Ultimax's.

I am going to guess that you had no room correction running with the Ultimax's. It is the only way the Rythmik would sound like an improvement.

Every sub need room correction, but especially a DIY sub like the Ultimax. The Ultimax does not have a flat frequency response. The Rythmik L12 has a flat frequency response only because it is running DSP inside of its plate amp.

Both my HT and bedroom setups are running DIRAC through MiniDSP's. Both setups have 99% of their bass performance extracted from the room. And the Ultimax is the undisputed champ.

There is no DSP within any Rythmik design.
 

Dj7675

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I completely disagree. I own a Rythmik L12 for my bedroom system. And I own 2 of the same DIY 18" Sealed Dayton Ultimax's powered by an iNuke6000 for my large HT.

The 18" Ultimax is in a different league, especially for high SPL listening. It easily competes with the likes of the SVS SB-16 and Rythmik F18. Now in my relatively small bedroom it would be way overkill and the Rythmik L12 is a wonderful sub to listen to for that space. In terms of bass quality, I prefer the Ultimax's in my large mid-field setup over my Rythmik in a small near-field setup. And the Dayton has the output equivalent of 8 Rythmik L12's. For $1400 to build two of them, there is no other product that can come close to the Ultimax's.

I am going to guess that you had no room correction running with the Ultimax's. It is the only way the Rythmik would sound like an improvement.

Every sub need room correction, but especially a DIY sub like the Ultimax. The Ultimax does not have a flat frequency response. The Rythmik L12 has a flat frequency response only because it is running DSP inside of its plate amp.

Both my HT and bedroom setups are running DIRAC through MiniDSP's. Both setups have 99% of their bass performance extracted from the room. And the Ultimax is the undisputed champ.
Hmm... I guess I’m trying to figure out what you disagree with my post on......
-They are smaller.... I mean much much smaller
-In my case, this means I have flexibility to position them to get a much flatter response (mitigate nulls). Right now they are in front right and back left corners.
-Having 2 provide plenty of output for me (For movies I listen at about -10db)
Not disputing the UM18-22 has more output because obviously it does. It is just that there are times when smaller subs have advantages too in regards to frequency response if the larger subs cannot be placed around the room to help provide smoother bass.
Basically pick the subs that get you flatish frequency response and the output you need. This will be different for different people/rooms
 

CumSum

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Hmm... I guess I’m trying to figure out what you disagree with my post on......
-They are smaller.... I mean much much smaller
-In my case, this means I have flexibility to position them to get a much flatter response (mitigate nulls). Right now they are in front right and back left corners.
-Having 2 provide plenty of output for me (For movies I listen at about -10db)
Not disputing the UM18-22 has more output because obviously it does. It is just that there are times when smaller subs have advantages too in regards to frequency response if the larger subs cannot be placed around the room to help provide smoother bass.
Basically pick the subs that get you flatish frequency response and the output you need. This will be different for different people/rooms

I disagreed with your assertion that the Rythmik L12 was an upgrade over the 18" Dayton Ultimax, but I see that was for your particular situation where the small size of the Rythmik L12 helped you get better placement which is very important to the sound. I just wanted to clarify that head to head, the Ultimax is a much better subwoofer in sound quality, output and value. But it requires room correction otherwise it will not sound very good.
 

Dj7675

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I disagreed with your assertion that the Rythmik L12 was an upgrade over the 18" Dayton Ultimax, but I see that was for your particular situation where the small size of the Rythmik L12 helped you get better placement which is very important to the sound. I just wanted to clarify that head to head, the Ultimax is a much better subwoofer in sound quality, output and value. But it requires room correction otherwise it will not sound very good.
Thanks for clarifying... agree with you on output. I would say with eq they both would sound the same. Value of course would be dependent on time spent, DIY skills etc. All the ultimax subs are a great DIY value for sure and are great subs. I had 2 UM18-22 for several years.
 

Bhh

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Hi guys, just wanted to thank everyone for such a great discussion following the review here. I’ve learned a lot and really appreciate everyone’s contribution.

As I mentioned earlier, Amir had a lot more tests planned for this and we just ran out of time since I’m on a short leash with regards to home auditioning this and there are so many delivery/shipping delays at the moment moving this thing from one coast to the other takes a while.

Thanks again,
B
 

Trdat

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Yeah, for sure. I'm not in the camp that would cross subs over at anything above 120hz. And even then I'd prefer to keep to 80 or 100hz in most cases. I can see the argument though, that if you already have multiple subs, especially if you're using 4 in the corners, that you might be able to achieve better quality 100-200hz by using the subs that high. Localization also seems like less of an issue in that case. .

I have dual 12 inch subs, sealed DIY and they can play well up to 200hz according to the frequency response measured in room. I am a big fan of crossing over at higher ranges purely because of the bigger bass. In saying that, after heaps of experimentation anything over 160 gets too boomy, and under 90 just does not cut it for the slam and bass your trying to achieve. To be perfectly frank, during listening sessions I change it around 150 for old skool techno and around 90 for most other genres and live recordings.
 

Trdat

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No and no.

The amplifiers are sourced from a manufacturer and then a daughter card added to implement the servo within the existing circuitry. The transducer has a small voltage feedback coil to provide the servo input, and there is also a small value resistor in series with the woofers driven coil (which is monitored across) to provide another input to the servo.

Brian Ding considers the specifics of all this proprietary. Suffice it to say, there's nothing fancy going on here at all. The concept is ages old.

Dave.


Are you suggesting we can DIY direct servo technology? How so? If I have understood correctly...
 

Trdat

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Wow thanks for kicking off subwoofers with the -to me- most interesting brand. To me, the most important thing about a subwoofer for music is the speed at which it can respond.

My suggestion for a subwoofer measurement would be to test its ability to track a square wave at E0 (20.602Hz) at a reference level. How fast can it incline and decline, and can it hold steady at the top and bottom of the square? I think that's where you'll really see a big difference in engineering quality.

I am not in-tuned with the science but I do agree that one of the most important aspects of a sub woofer is its repeated capability of continuously producing bass notes with how fast it can stop and start.

Although, I have come across many discussions(personally) where experts vehemently deny that anything like fast bass exists even an amateur audiophile understands that wavelengths at that frequency are slow. But there is no doubt that a sub must exist that produces this type of bass and it should be number one on a measurement list to define a subs quality. I know an impulse response gives us a lot but something should be invented in terms of testing for a continuous barrage of repeated bass.
 

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RayDunzl

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I am not in-tuned with the science but I do agree that one of the most important aspects of a sub woofer is its repeated capability of continuously producing bass notes with how fast it can stop and start.

Let's look at a woofer.

Experiment:

A "tick" as a time alignment tool
35Hz sine test tone
Fade in over one cycle so it doesn't "click" too much at the beginning of the wave.
Output via JBL LSR 308

First Trace - test signal
Second trace - the in-room response (with some EQ)
Third trace - the in room response - defeated the EQ in case that was making trouble.

You see the tick, and its echoes in the room
Then the recorded "bass" tone.

I wonder if this bass is slow or fast.

1585120218894.png


Forgot to try the stop part, and included time scale. Had to zoom out a little...

1585120747824.png
 
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RayDunzl

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Francis Vaughan

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I am not in-tuned with the science but I do agree that one of the most important aspects of a sub woofer is its repeated capability of continuously producing bass notes with how fast it can stop and start.

Although, I have come across many discussions(personally) where experts vehemently deny that anything like fast bass exists even an amateur audiophile understands that wavelengths at that frequency are slow. But there is no doubt that a sub must exist that produces this type of bass and it should be number one on a measurement list to define a subs quality. I know an impulse response gives us a lot but something should be invented in terms of testing for a continuous barrage of repeated bass.

There is a curious sort of mental model that thinks that a sound source like say a bass drum can only be reproduced by a sub-woofer, and so the slam of a bass drum might become muted and "slow" if the sub-woofer is not "fast" enough. But there is nothing special about a bass instrument. All instruments have energy across a wide range of frequencies. Apart from say a flute, musical instruments are awash with harmonics. Violins are a sawtooth, over-driven electric guitar is a square wave at heart. We don't get worried that the mid-bass driver is unable to reproduce the thrash and yowl of these instruments. That is the job of the tweeter. Bass is no different.
Of course integrating the energy from the various drivers isn't trivial. Time delays, and importantly, group delay matter. But once got right that slam you want is going to be there perfectly.
The answer is most certainly not in trying to create some sort of high bandwidth sub-woofer. That is a recipe for all manner of horrors, not the least of which will be making integration with other speakers impossible at a fundamental level.

Impulse response is just one way of representing the response. It is the dual of frequency response. Albeit with some advantages and some problems when used in real life. A continuous barrage of repeated bass won't tell you anything other than the thermal properties of the sub. You will find everything that characterises the sub in that one impulse response. The trick is using the transforms to tease it out into more easily digested form. Taking the fourier transform of an impulse gets you the complex frequency response (which is a fancy way of saying frequency response and phase.) There is enough to get things like group delay and the like. It is all there.
 

RayDunzl

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Apart from say a flute, musical instruments are awash with harmonics

Not to disagree too much, but...

The flute spectrums I've looked at had plenty of harmonic content.

1585123318795.png


The closest I've come to a pure sine here at the house is blowing across the top of a beer bottle. 2nd harmonic down over 40dB


1585123277919.png


And, here is the electrical signal of a single bass guitar note awash with harmonics. It took several tries to keep the 2nd harmonic level lower than the fundamental:

1585123491745.png
 

RayDunzl

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The better beer bottle image:

Grolsch 330ml Beer Bottle. 0.4% THD.

Not bad...

1585123936267.png
 

QMuse

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Not to disagree too much, but...

The flute spectrums I've looked at had plenty of harmonic content.

View attachment 55680

The closest I've come to a pure sine here at the house is blowing across the top of a beer bottle. 2nd harmonic down over 40dB


View attachment 55679

And, here is the electrical signal of a single bass guitar note awash with harmonics. It took several tries to keep the 2nd harmonic level lower than the fundamental:

View attachment 55682

I believe that frequency of the fundamental tone of the beer bottle can be changed by varying the content of the beer inside. :D
 
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DonH56

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How do they do the HT modes, PEQ and low pass?

All analog circuits. That is the way I designed my DIY sub way back around 1980 before DSP was really a thing. Analog filters (EQ), feedback control (LDI -- linear, differential, integral), and delay ("phase") adjustment (using an analog all-pass filter). People tend to forget that DSP "everywhere" is a fairly recent innovation in the history of electronics, and often a simple analog design is easier and cheaper to implement. As an analog guy I am biased, natch, but I do have a fairly deep experience with DSP and if I were doing it today would likely go that route using a miniDSP or some other processing solution (got Mitch's book, have not had time to buy the SW and play with it).
 
D

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Are you suggesting we can DIY direct servo technology? How so? If I have understood correctly...
Certainly. In fact, that's exactly what Rythmik does. Their amplifiers are sourced from somebody else and then modified in-house to implement the servo scheme. They spec drivers with the small coil for this application.
DIY servo approaches of this sort have been around for many decades. I can remember seeing a DIY servo subwoofer project in Audio Amateur magazine back in 1976, or so.

That said, I don't see much point in DIY'ing when something like the L12 is available for just $550. A person could tear it apart and fiddle for a good learning experience though.

Dave.
 
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