What To Do?

[speakerman39]

Congrats.. Now you can enjoy yoru sub without fretting about if you purchased the best sub for your needs.

That is correct. Can't send a B-stock back. Once it is here I am stuck with it regardless. Really doesn't matter anyways as I would NOT pay for the shipping back on the ULS-15 MK2. The L12 is costing me $50 to send it back. That hurts enough. Just have to see how I like ULS-15. Chances are, I will be more than happy!

Cheers,

Phil

 

[shadyJ]

That looks like it is in the inch range to me (but hard to get any precision)!
What do you think, Shady?
My understanding of the Servo system is that it offers an added level of control which keeps the drivers behavior linear, so where a driver might have to be "over-designed" to get 1" of linear throw, with servo, that same driver might get 1-3/4" linear throw.
I am not sure the Rythmik Servo subs can be gauged using the same yardstick as the typical designs.

It's hard to say how far it is. An inch maybe, but how much of that throw is linear is the question. That is why you need to have an RTA present with a test tone.

As for added control, once the coil gets too far from the gap, the cone is out of control. I don't think anything can help it at that point. The servo technology looks to help reduce non-linear motion, but I am guessing it only really helps when the moving mass of the driver is already under control of the motor. If the coil is in a magnetically wonky area or if the suspension is beginning to inhibit linear travel, I don't see how a feedback mechanism can correct for that.

 

[KEW]

It's hard to say how far it is. An inch maybe, but how much of that throw is linear is the question. That is why you need to have an RTA present with a test tone.

As for added control, once the coil gets too far from the gap, the cone is out of control. I don't think anything can help it at that point. The servo technology looks to help reduce non-linear motion, but I am guessing it only really helps when the moving mass of the driver is already under control of the motor. If the coil is in a magnetically wonky area or if the suspension is beginning to inhibit linear travel, I don't see how a feedback mechanism can correct for that.

Okay, totally making up numbers here, but say 1 watt moves the driver 0.1" in the "safe" linear zone. However, in the "wonky" zone, it only moves 0.08" for an additional 1 watt. The servo is monitoring it in real time and sees it is not moving far enough to maintain linearity, so it compensates by sending ~1.2 watts thus maintaining linearity in a non-linear region for the given driver.

edit: I realize that the relationship between wattage and displacement is not linear, but let's just go with it for the purpose of this attempt at an explanation. trying to work in a logarithmic relationship with only convolute things.

 

[3db]

It's hard to say how far it is. An inch maybe, but how much of that throw is linear is the question. That is why you need to have an RTA present with a test tone.

As for added control, once the coil gets too far from the gap, the cone is out of control. I don't think anything can help it at that point. The servo technology looks to help reduce non-linear motion, but I am guessing it only really helps when the moving mass of the driver is already under control of the motor. If the coil is in a magnetically wonky area or if the suspension is beginning to inhibit linear travel, I don't see how a feedback mechanism can correct for that.

Instead of tossing out information that may be incorrect, I suggest talking to either Brian Ding or Enrico to get the correct information. You make far too many assumptions in your analysis.

 

[shadyJ]

Okay, totally making up numbers here, but say 1 watt moves the driver 0.1" in the "safe" linear zone. However, in the "wonky" zone, it only moves 0.08" for an additional 1 watt. The servo is monitoring it in real time and sees it is not moving far enough to maintain linearity, so it compensates by sending ~1.2 watts thus maintaining linearity in a non-linear region for the given driver.

edit: I realize that the relationship between wattage and displacement is not linear, but let's just go with it for the purpose of this attempt at an explanation. trying to work in a logarithmic relationship with only convolute things.

I see what you are saying, but there seems to me a couple problems with your example. First of all, by 'wonky' zone, I mean where the permanent magnet field loses its predictable strength over the voice coil. This usually happens when the coil leaves the magnetic 'gap' of the top plate. It would be hard to precisely compensate for that when the magnetic field is unpredictable. At this point the driver is past xmax, the cone/VC assembly is not in a well-controlled region, and I don't see a servo mechanism faring any better here than conventional designs. I would guess that the servo mechanism can only control the moving assembly when motor itself is in control of the moving assembly. I see the servo mechanism as a fine-tuning of the motion of the woofer on top of that of the driver. The case may be, the worse the driver, the less effective the servo mechanism. But the problem with that would be, the better the driver, the less the servo is needed. Perhaps there is a point of of driver quality where servo technology holds a maximum return. That is speculative, of course, and the guy who knows the answers is Brian at Rythmik.

 

[shadyJ]

Instead of tossing out information that may be incorrect, I suggest talking to either Brian Ding or Enrico to get the correct information. You make far too many assumptions in your analysis.

I qualified all of my statements that they were just guesses, not concrete data. But I would love to know how the servo feedback system holds an advantage in regions where the driver motor itself is losing control of the moving assembly. The theory behind servo feedback would not seem to be beneficial at this point, as far as I understand it. It can not make a driver better than its physical limitations, it can only make better use of the driver's abilities.

 

[PENG]

I qualified all of my statements that they were just guesses, not concrete data. But I would love to know how the servo feedback system holds an advantage in regions where the driver motor itself is losing control of the moving assembly. The theory behind servo feedback would not seem to be beneficial at this point, as far as I understand it. It can not make a driver better than its physical limitations, it can only make better use of the driver's abilities.

I agree with your concept but are you assuming the driver in the Rythmik in fact has a lower limit or that is one of your "guesses? That could be one of the assumptions 3 dB referred to..

 

[3db]

I agree with your concept but are you assuming the driver in the Rythmik in fact has a lower limit or that is one of your "guesses? That could be one of the assumptions 3 dB referred to..

I'm not guessing at any thing Shady nor am I making any assertions to how the servo behaves and how and when it corrects the movement of the coil. I wont pretend to guess how it works. All I'm saying is get the facts from Rythmik and translate into English so that everyone understand whats going on.

 

[shadyJ]

I agree with your concept but are you assuming the driver in the Rythmik in fact has a lower limit or that is one of your "guesses? That could be one of the assumptions 3 dB referred to..

I am not sure what you mean by lower limit?

 

[PENG]

I am not sure what you mean by lower limit?

cone excursion, didn't you mention something about that before?

 

[PENG]

I'm not guessing at any thing Shady nor am I making any assertions to how the servo behaves and how and when it corrects the movement of the coil. I wont pretend to guess how it works. All I'm saying is get the facts from Rythmik and translate into English so that everyone understand whats going on.

My questions were directed to shady, not you at all.

 

[3db]

I questions were directed to shady, not you at all.

Oops Sorry PENG. For some absurd reason, I thought Shady posted that.. Must have been multitasking or something during the reply . *lol* That was supposed to be my response to post 86.

 

[shadyJ]

cone excursion, didn't you mention something about that before?

Still not sure what you mean. Of course the driver will be excursion limited at lower frequencies, at least. The sub is likely amp limited at upper bass frequencies.

 

[Nate Heidne]

Do it, you won't regret any of it

 

[PENG]

Still not sure what you mean. Of course the driver will be excursion limited at lower frequencies, at least. The sub is likely amp limited at upper bass frequencies.

I am going to try one more time as I am not sure you are just avoiding the simple question by playing with words. Of course we all know everything has limits but you were comparing the SB2000 and the L12 if I remember right.

In my post#87 I asked whether your talk about the SVS' driver having more throw than the Rythmik was an example one of the guesses or assumptions you made. If it is then I can see 3db's point. I used the word limit because to me you were implying the Rythmik L12 was driver limited in terms of "throw" relative to that of the SB2000, to the point that the servo amp feature cannot offset this advantage. If you still don't understand my simple question then don't bother, and thanks anyway.

 

[shadyJ]

I see what you mean. You didn't specify limited with respect to the SB2000, and I thought you were referring to the servo drive alone which is why your question seemed weird. I don't know that the SB2000 does have a greater xmax than the L12, but I think it probably does, although not a whole lot more. As I said, I don't understand how a feedback correction system could help when the motor is losing control of the voice coil. If there is a disagreement on these points, that is fine, as this is all easily testable. If anyone has these subs and a halfway decent calibration mic, they can test any of these predictions.

 

[3db]

I see what you mean. You didn't specify limited with respect to the SB2000, and I thought you were referring to the servo drive alone which is why your question seemed weird. I don't know that the SB2000 does have a greater xmax than the L12, but I think it probably does, although not a whole lot more. As I said, I don't understand how a feedback correction system could help when the motor is losing control of the voice coil. If there is a disagreement on these points, that is fine, as this is all easily testable. If anyone has these subs and a halfway decent calibration mic, they can test any of these predictions.

I've since played that piece quite a bit louder than what I had recorded on that you tube video and I still didn't hear anything bad coming out of the sub. It did scare me a little doing it because I don't want to damage the sub. I didn't hear any thumps or anything indicating that driver hit its hard limits. The feedback mechanism is to prevent losing control of the driver but I suppose, it can compensate for stupidity.

 

[PENG]

I see what you mean. You didn't specify limited with respect to the SB2000, and I thought you were referring to the servo drive alone which is why your question seemed weird. I don't know that the SB2000 does have a greater xmax than the L12, but I think it probably does, although not a whole lot more. As I said, I don't understand how a feedback correction system could help when the motor is losing control of the voice coil. If there is a disagreement on these points, that is fine, as this is all easily testable. If anyone has these subs and a halfway decent calibration mic, they can test any of these predictions.

I did say I agreed with your concept. However, the validity of your claim hinges on your assumption/guess that the SB2000 driver has more "throw", albeit your guess could well be an educated one as I am quite sure you know a lot about subs regardless of your apparent bias towards one particular brand. So yes I agree the servo (basically a feedback system) design can enhance and/or make better use of, but cannot extend the physical travel limit ("throw") of the driver. I admit when I used the word "lower limit" I should have said "lower cone travel limit than that of the SB2000...or something like that".

 

[Steve81]

I don't pretend to understand the servo, and I have yet to see a review where they really provide any measurements of what the servo provides (I guess it would be almost impossible to isolate the servo though it seems you could disconnect the wires providing the feedback loop).

Since it seems to be a continuing topic here, I'll chime in with a few cents. There are a couple good sets of measurements of Rythmik subs to look at, the FV15HP by Josh and a sealed DIY 12"er by Ilkka.

http://www.data-bass.com/data?page=system&id=51&mset=50
http://www.hometheatershack.com/forums/subwoofer-tests-archived/5756-diy-rythmik-audio-direct-servo-12-sealed-56l.html

Now there are obviously limits as to what the servo can do. You can see from Ilkka's data set on the that distortion can only be controlled to a point. However, one area where both measurements agree is with respect to compression. If you look at Josh's chart titled "Long Term Output Compression (Magnitude)", you'll see just how neatly its controlled by the servo mechanism. Obviously port compression is still an issue, but that's clearly beyond the scope of what the servo can deal with. The story is similar in Ilkka's testing. Aside from where the driver is displacement limited, output increases at a predictable rate.

 

[KEW]

Since it seems to be a continuing topic here, I'll chime in with a few cents. There are a couple good sets of measurements of Rythmik subs to look at, the FV15HP by Josh and a sealed DIY 12"er by Ilkka.

http://www.data-bass.com/data?page=system&id=51&mset=50
http://www.hometheatershack.com/forums/subwoofer-tests-archived/5756-diy-rythmik-audio-direct-servo-12-sealed-56l.html

Now there are obviously limits as to what the servo can do. You can see from Ilkka's data set on the that distortion can only be controlled to a point. However, one area where both measurements agree is with respect to compression. If you look at Josh's chart titled "Long Term Output Compression (Magnitude)", you'll see just how neatly its controlled by the servo mechanism. Obviously port compression is still an issue, but that's clearly beyond the scope of what the servo can deal with. The story is similar in Ilkka's testing. Aside from where the driver is displacement limited, output increases at a predictable rate.

What I was really referring to was a comparison of "with" vs "without" servo so we can see what, exactly, the servo adds!
That may be impossible.