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#21 Ricci

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Posted 07 April 2016 - 06:14 PM

I watch It's Always Sunny too. Another favorite for mindlessly stupid and funny was Blue Mountain State. The "oil change" episode was priceless. I'm not following on ATHF either? What's that?



#22 Ricci

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Posted 07 April 2016 - 06:17 PM

Not sure if this thread is for quick side-topics but I'll take my chances of getting Beast-like infractions. :). Anyway, here's something interesting on Audio Fluidization regarding landslides, which basically means the deep bass from rocks crashing create vibrations, which in turn reduces the friction resulting in longer landslides. This had been predicted in the late 70s but computers weren't powerful enough to simulate it until recently.

http://www.engadget....ow-like-rivers/

 

Very cool. That's exactly what this thread is for.

There's a pm group of about 6 of us that's probably been going on for a couple of years and the topics are all over the place but there has been some really good technical discussion as well that got some of us thinking that it was a shame it wasn't public. Figured it might be time for a thread for whatever.



#23 Ricci

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Posted 07 April 2016 - 06:24 PM

To both Lilmike and Ricci - my large coil adjustment method works.

 

 

I don't doubt the method. I checked it and read the paper when you sent it to me. It works quite well. Not 100% dead nuts but very close and worlds better than not using it. It's a good thing somebody took the time to verify and easy button it. I give you props there.

 

I still hesitate to trust it for complicated high order alignments, with unknown drivers, where you are using your best assessment and judgment from the info given. That's just me though. I wonder have you simulated a driver like the old MTX 9515 or the LMS 5400 and used it? I have not. Those are outlier drivers that despite having huge coil mass behave close to expected without the "large coil" tweak. Of course those types of drivers are few and far between.



#24 Ricci

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Posted 07 April 2016 - 06:53 PM

I'm not sure if you are referring to my remark in the SI DS4-18 thread, but just to clear things up, I don't doubt for any instant that your testing pushes the drivers to their excursion limits.  My comment concerned the visibility of Le non-linearities, which may not be revealed very well in your sine-sweep tests.  The reason is that your tests don't measure high frequency distortion *while the driver is simultaneously being pushed to full excursion*.  By the time the sine sweep hits the high frequencies where Le modulation is likely to show up, the driver just isn't being pushed out to its limits any more.  Only with an impractically large amp would it be possible to do this with sine sweeps.

 

Wasn't referring to your remark. I had meant to respond to it but forgot.

 

I agree that this is something that would be very intriguing to look at. It's been discussed a few times years ago. I even tried a few things at home but couldn't work out a feasible, quick way to get it done with what I had to work with. I don't think the spectral contamination the way Illka or myself tried to do it was a good way for a few reasons. Firstly generating the spaced individual tones as part of one signal took some work with NCH tone generator. It'd be best to work it into a wav file sample that could be triggered. That wouldn't be too hard. Most of the RTA or spectrum analyzer settings I looked at required quite a bit of time to settle in and capture the content with high resolution. The signal was murder on the systems. At least it sounded like they were dying a quick death. Even at levels well below maximum the spaced non harmonically related tones sounded awful. I couldn't really tell too much between different systems using it when looking at the recorded spectrum. In short difficult to setup, took time, caused a ton of heat in the voice coil, didn't clearly show much difference visually and made me fear damage to the drivers worse than any other signal I've ever used.

 

A lot better option would be to use a sine tone to produce large driver excursion and then run pink noise or perhaps a sweep through and capture it that way. I'd lean towards PN on this I think. Logistically though there are a lot of questions. How do you standardize this? Each system has a different native FR such that some frequencies are emphasized more than others. Do they get EQ'd flat? This alone becomes a ton of work. Let's assume no. What excursion level is the driver pushed to? That is difficult to standardize. Do we settle on a normalized voltage versus impedance? What frequency of sine wave is used to generate the driver excursion when impedance varies widely as does the resonance of the system and excursion profiles? 40v into one driver might cause 20mm with a 15Hz sine while another might be at only 12mm. I'd guess that you would want multiple measurements with the driver excursion pushed to various levels. I'd like to see how things change at higher excursion versus lower as would everyone I assume. What level is the PN or sweep signal for the response shape relative to the sine signal producing driver excursion? Equal? Do they both get scaled by the same amount for each measurement?

 

This is the kind of stuff I start thinking about with new measurement types. It has to be relatively quick, easily setup (relative to the gamut of other stuff already being done), intuitive to interpret the results and standardized enough that the results from various drivers can be compared meaningfully. If it takes a dedicated reconfigure of the measurement gear or an hour and a half to complete it for one system I'm just not going to be able to include it. I'm all for doing something like this but would need some help figuring out the best way to tackle it and standardize it.



#25 diy speaker guy

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Posted 07 April 2016 - 07:30 PM

I don't doubt the method. I checked it and read the paper when you sent it to me. It works quite well. Not 100% dead nuts but very close and worlds better than not using it. It's a good thing somebody took the time to verify and easy button it. I give you props there.

 

I still hesitate to trust it for complicated high order alignments, with unknown drivers, where you are using your best assessment and judgment from the info given. That's just me though. I wonder have you simulated a driver like the old MTX 9515 or the LMS 5400 and used it? I have not. Those are outlier drivers that despite having huge coil mass behave close to expected without the "large coil" tweak. Of course those types of drivers are few and far between.

 

Both the 9515 and the LMS were measured by you and were included in the study.  Both of them simulated closer to your measurements with the adjustment than without.

 

In addition, the LMS was measured by you in both the sealed box AND the Othorn IIRC, and in both cases the simulations were closer to the measurements with the adjustment than without.

 

Sure, sims with those drivers aren't incredibly inaccurate even without the adjustment but the adjustment does make things closer to reality.

 

Just for the record, normalized inductance (Le/Re) for a few examples (t/s measured by you):

 

Dayton UM 18 = 0,36

Dayton HO 18 = 0.4

MTX 9515 = 0.4

LMS 18 = 0.94

UXL 18 = 1.63

FI SSD 18 = 3.07

 

In general the ones with the higher normalized inductance are the ones that deviate the most from the normal (unadjusted) sims.  Although it's not totally linear there is a pattern, this is the charted data for normalized inductance (Le/Re) vs Bl multiplier (the amount I had to adjust Bl in the sim to make the sim match the measurement).

 

35co94g.png

 

Looking back at the paper, the sample size was 22 drivers (every driver of this type measured by data-bass), some of which were measured in multiple enclosure, so there were 30 measurements.  (Not 50 like I said before, not sure why I thought that.

 

A larger sample size would help to make the generic adjustment method better, because as you can see the dots on the chart don't follow the line perfectly but you can see a very distinct trend.  And the trend line is mathematical equivalent of the generic adjustment formula.

 

Even better results are had if you don't use the generic adjustment but use the curve fit method for the particular driver (the method that was used to derive the generic formula).  This requires measured t/s parameters and a sealed box measurement though.  But if you have those you just adjust Bl until the sim matches the measurement and that's the Bl value you should use for subsequent sims with that driver.

 

So yeah, the LMS and the 9515 and all of the rest of the 22 driver samples all simulated closer to the measurements with the adjustment than without, in sealed, ported and horn enclosures.  And yeah, I trust the method enough to design horns.  I'd probably use the curve fit method  with measured t/s and a measured sealed box FR (not the generic formula) for a big expensive horn, but the point is that I trust it.  I'm not saying the method is perfect but it's close enough to design with and much closer than not using it at all.

 

Without measured t/s parameters at the very least, forget it.  If you don't have at least that you probably won't get a good result from this type of large excursion driver no matter what you do.



#26 maxmercy

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Posted 08 April 2016 - 12:42 AM

I watch It's Always Sunny too. Another favorite for mindlessly stupid and funny was Blue Mountain State. The "oil change" episode was priceless. I'm not following on ATHF either? What's that?

Aqua Teen Hunger Force.  Idiocy at its best, but hilarious at times.  Episodes are either great or trash, not real in-between, and best of all, only 12 mins long.

 

JSS


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#27 BeastAudio

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Posted 08 April 2016 - 02:11 PM

Aqua Teen Hunger Force.  Idiocy at its best, but hilarious at times.  Episodes are either great or trash, not real in-between, and best of all, only 12 mins long.

 

JSS

 

Wow, blast from the past. I used to watch a little of that, but never got heavy into it.



#28 Bossobass Dave

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Posted 08 April 2016 - 05:25 PM

I'll start off with some points I wanted to make related to discussion in another thread that is getting way off topic. Each one of these subjects could be its own topic.

 

3.)There has been a few remarks about not knowing whether the driver was pushed to the excursion limits during the max long term or burst tests here. EVERY driver has been. There is no question about this. The burst testing is only stopped when there is a clear indication of driver distress (usually mechanical noise) in the deep bass or the amp runs out. Below 30Hz the amp never runs out. The one case was the XXX overhung coil. The amp clipped right about the time the driver was done anyway. This was because the suspension had tightened dramatically and the motor had lost a ton of force with the coil that far from center in an undersized box. Same thing with the long term testing. That test is almost always stopped by driver excursion and bad noises indicating mechanical limitations are imminent. Severe thermal compression in the upper bass of 3dB or more is another good sign to stop but this almost always occurs at a point where the driver is out of excursion anyway. The CEA-2010 data may not be the maximum output of the DUT. That info is also available for nearly all systems though under the static charts section. The numbers in red are the maximum level attainable by the device limited by driver excursion. In the case of the XXX you could mount it IB and it will never put out more than about 111dB at 20Hz same as in the 4 cube cab. Power required will go way down as would distortion but that is the displacement limit. It is not going to put out any more maximum SPL in the deep bass. The 2-120Hz sweep used for the long term test covers the entire bass FR. While you may see slightly more output from a system with the CEA-2010 or MAX bursts broad band there will usually be one band or another that is very close. Note that the bursts are 1/3rd octave spaced. The sine sweep covers every frequency in the bandwidth and it will find the worst case frequency for induced driver excursion in the sealed cab. It may be a very narrow small area, but if the driver threatens to blow apart or smash itself to death there, that becomes the voltage limit for the long term testing. If the driver coil doesn't melt first of course. Some drivers like the XXX this occurs up near the impedance peak at 30Hz due to the high qtc and resultant excursion profile. Others such as the 19 with a very low qtc in the same cab are limited by excursion at 10Hz or lower rather than 20-30hz.

 

 

 

 

Of course, you know I disagree with the notion that every driver has been optimally tested regarding excursion. This is only because readers split decibels as though they were truckloads of food in a world of starving people.

 

As I mentioned in the other thread, a small sealed box does several things, among which, being the most relevant on this subject, it induces asymmetrical (non-linear) excursion. This causes an increase in THD and changes excursion measurements.

 

There is no chance that mounting the XXX in 4 cubes vs in an IB will result in zero difference other than required input power.

 

Without an accurate means to measure excursion, you simply can't make that assumption. Anyone would have to agree that comments like; "It looked like the cone was moving about 25 mm in one direction...", "...mechanical noise set in" are absurdly inaccurate gauges for actual excursion behavior and distances.

 

In any case, my argument was not whether or not the driver was pushed to full excursion. It's the CEA 2010 number that matters, not the obscure no-THD-limit number. If the XXX excursion capability claims are anywhere near accurate, it should be capable of AT LEAST +3dB more output than the RF 19" driver. Instead, the results show the XXX giving -6dB less. That's a 9dB swing for a single driver.

 

To test a "DIY" driver (vs a commercial subwoofer "system"), each driver should be in a Vb that yields a calculated Qtc of .707. Otherwise, especially when comparing an extremely low Qts driver like the original LMS-Ultra-18" or RF-19" to the extremely high Qts RE-XXX, the CEA-2010 burst numbers are meaningless as a comparative tool.

 

Of course, that's not practical. Instead, there should be a calculator for HT eligibility that factors box size. There are enough program savvy readers out there who could whip that up toot suite if there was ever a discussion about the parameters instead of the go-zillion discussions about which driver posted higher CEA numbers.

 

Personally, I don't care either way. There are many more important factors in designing and building a subwoofer system for HT Than yakking over 3 mm of Klippel verified one-way throw. But, to dismiss the fact that every driver is tested in the same box by referring to a metric that I believe is all but useless begs a differing opinion.


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#29 lilmike

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Posted 08 April 2016 - 05:55 PM

"As I mentioned in the other thread, a small sealed box does several things, among which, being the most relevant on this subject, it induces asymmetrical (non-linear) excursion. This causes an increase in THD and changes excursion measurements."

 

Thanks for posting this Dave. Sometimes, I miss the obvious. 



#30 lilmike

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Posted 08 April 2016 - 06:22 PM

@ DIYSG

 

"To both Lilmike and Ricci - my large coil adjustment method works.

 

I developed it by curve fit matching MANY sims to measurements with a very simple adjustment.  And then the cherry on top was when Ricci posted the measurements of several long excursion drivers in Othorn and my method worked remarkably well - the adjusted sims had a much higher degree of accurate correlation to the measurements than normal sims and that's when I knew for sure it really worked."

 

I never meant to imply that it doesn't. I read the paper on the day that you linked me to it. I don't dispute your results at all, and I applaud your efforts in figuring out what needs to be adjusted to "match" things. 

 

Since you've demonstrated that there is a clear need to "adjust" things and showed us a way that works, I am left questioning the simulation tools I rely on. That throws my "trust the math" assumption out the window, which is a fundamental one I was taught early on when it comes to computer modeling. I am pretty sure that I'm not nearly smart enough to vet, let alone write, my own simulation codes. I can still measure the inputs and the results though, and I am reasonably-good at making the actual build match the model.

 

We're just coming at the problem from different directions. I can definitely see the correlation in your work, I am searching for causation. I want to understand the "why". See, "B" is, and "L" is. These are both pretty basic fundamental physical characteristics of a moving coil permanent-magnet motor. While I can't measure either B or L directly with my gear, the BL product can be easily and accurately measured. "Adjusting" it just flies in the face of my "measure the inputs" rule. The biggest question I have now is what "input" are we not measuring correctly or accurately? 

 

What's the missing piece? It certainly appears to be related to inductance. Certainly, larger coils and motors have larger issues with keeping inductance effects in check. As you state, even with the additional inductance parameters measured, most simulation software doesn't know what to do with the additional information. 

 

Again, I really want to make this clear. I am asking questions so that I can understand what is going on, I'm not questioning your approach, or the need to do something different. If I can't "trust the math", I need to know when to worry and what to change, because I am working with some large-coil/long-throw drivers right now. 


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#31 Ricci

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Posted 08 April 2016 - 06:33 PM

Mike I think a few of us are wondering those same things. See the reduction of BL method does work quite well at matching the overall response shape, however sometimes it can result in the sensitivity being off some. If you tweak the LE as well you can get a bit closer still in some cases. Unibox has the ability to use a 3 part complex inductance (requiring measurements because no one publishes this) and if you combine this more detailed inductance model with tweaks to the BL it can get even closer still. I found that even with Unibox's inductance model I still couldn't get a close enough match. Most of the commonly used simulators don't even have this ability either. As to why the BL tweak works, when as you say those parameters should be verified and known that is the question. I believe it does have to do with inductance but how exactly I've not spent much time considering. If you haven't tried the "large voice coil" option in HR give it a shot.



#32 diy speaker guy

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Posted 08 April 2016 - 06:59 PM

Yeah, I never studied why, only how to sim more accurately.

 

It does present as though the motor strength is less than the t/s specs indicate in terms of qtc, although the bl adjustment does leave the adjusted sim a couple db less than the measurement (this part was never addressed in the generic formula).

 

It does appear to have something to do with inductance BUT drivers like the UM and HO (as measured by data-bass) have remarkably low normalized inductance, .36, .4.  There are pro drivers have have higher normalized inductance that don't appear to suffer from this issue.

 

I wondered if the 3 point complex inductance model would fix the sims, Ricci just answered that question,  It appears it won't.

 

Djim brought up this in a diyaudio discussion about this issue:

 

 

 

The force field (BL) is a constant and cannot change. Losses have to be compensated with Re. The problem here is in the inductive reactance (XL), which opposes the change in current and becomes the dominant force here. You can increase or lower this force by increasing or lowering the force field (BL).  If you look for driver indications: high Le and/or high Mms (for its size) in relation to a low EBP value.
 
 
Driver_Overview_03.jpg
 
That chart was included in his post but I can't get it in the quote.  Trying to fight the formatting lost most of my post so I'll have to retype the rest.


#33 diy speaker guy

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Posted 08 April 2016 - 07:16 PM

I haven't looked into the info in that post very carefully, perhaps I should.  But when it comes to reactive inductance, higher math and imaginary numbers, that's where the math goes above my head.

 

There are pro drivers that have higher normalized inductance than some of these large excursion driver (like UM and HO, normalized inductance is very low as measured by data-bass) and the pro drivers don't seem to suffer from this issue while even the lower normalized inductance high excursion drivers do.  i don't know why.

 

I do know that my early adjustments involved adjusting Re instead of Bl, but (IIRC) the Bl adjustment turned out to be faster, easier and more accurate.  The Re method made for a significant sensitivity change (obviously) and it was just to hard to fix that in a generic way.  The Bl adjustment always leaves sensitivity a couple db lower than the measurement but I didn't bother to do anything about that issue.  It's pretty consistently a couple db though.

 

The Bl method does not seem to give as accurate impedance results as an unadjusted sim - the difference is small and it's just the width and height of the impedance peaks that were off, not the frequency of the peaks IIRC, so it was decided to use the adjusted FR and excursion for the Hornresp generic adjustment but to leave the impedance unadjusted.  This really bothered me but I couldn't think of a way to resolve that.

 

Because of the question brought up by that, and the sensitivity being a couple db low, it was decided to make the "large coil" adjustment only available in the Loudspeaker Wizard, not in the main program.  I was ok with that because I don't use the generic adjustment anyway, I use the Bl values that I derived when adjusting the sims to match the measurements, which will obviously give a more accurate result.  Subtle in most cases, but some of the drivers were clearly outliers in the chart I posted showing normalized Le vs Bl multiplier.

 

The point here is that I'm not a driver designer or physicist, I didn't even try to study why these large excursion drivers don't sim accurately.  i just don't know.  Maybe it has something to do with Djim's post, maybe not.  All I know is that when faced with a problem, I start with the most accurate inputs I can.  In this case that didn't help but I did notice that the measurements at data-bass looked remarkably similar to sims where I had added a bit of Re to simulate heavy power compression.  I tried adding a bit of Re, it worked.  I refined the method with the help of LTD02 and David McBean and it got pretty good and I was able to make it a generic formula.

 

So I have no idea why it works or why it's even necessary for this type of driver.  But it does work.


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#34 diy speaker guy

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Posted 08 April 2016 - 07:24 PM

Of course, you know I disagree with the notion that every driver has been optimally tested regarding excursion. This is only because readers split decibels as though they were truckloads of food in a world of starving people.

 

As I mentioned in the other thread, a small sealed box does several things, among which, being the most relevant on this subject, it induces asymmetrical (non-linear) excursion. This causes an increase in THD and changes excursion measurements.

 

There is no chance that mounting the XXX in 4 cubes vs in an IB will result in zero difference other than required input power.

 

Without an accurate means to measure excursion, you simply can't make that assumption. Anyone would have to agree that comments like; "It looked like the cone was moving about 25 mm in one direction...", "...mechanical noise set in" are absurdly inaccurate gauges for actual excursion behavior and distances.

 

In any case, my argument was not whether or not the driver was pushed to full excursion. It's the CEA 2010 number that matters, not the obscure no-THD-limit number. If the XXX excursion capability claims are anywhere near accurate, it should be capable of AT LEAST +3dB more output than the RF 19" driver. Instead, the results show the XXX giving -6dB less. That's a 9dB swing for a single driver.

 

To test a "DIY" driver (vs a commercial subwoofer "system"), each driver should be in a Vb that yields a calculated Qtc of .707. Otherwise, especially when comparing an extremely low Qts driver like the original LMS-Ultra-18" or RF-19" to the extremely high Qts RE-XXX, the CEA-2010 burst numbers are meaningless as a comparative tool.

 

Of course, that's not practical. Instead, there should be a calculator for HT eligibility that factors box size. There are enough program savvy readers out there who could whip that up toot suite if there was ever a discussion about the parameters instead of the go-zillion discussions about which driver posted higher CEA numbers.

 

Personally, I don't care either way. There are many more important factors in designing and building a subwoofer system for HT Than yakking over 3 mm of Klippel verified one-way throw. But, to dismiss the fact that every driver is tested in the same box by referring to a metric that I believe is all but useless begs a differing opinion.

 

If they are all tested in the same box they all "see" the same asymmetrical air spring.  Your proposed method of testing in different box sizes would mean they would all see a wildly different air spring.  The only way to eliminate that as a factor would be to test in IB.  There are a bunch of reasons that would be preferred to testing every driver in a different box size, some of which would require dramatically different sizes to obtain the same qtc.  Anybody can use any driver in any size box from very very small to IB and there can be very good arguments for any given size based on design goals.  So basing all testing on a qtc value isn't going to make the tests any more standardized except in the single metric of qtc.  Nobody is going to build a .7 qtc box for a XXX anyway.  They are either going to use it in a small box or in IB.  The chances that someone would make a huge sealed box just to get a .7 qtc are slim so what would be the point of testing in that box size?  In this world of flat packs most people are going to stick their drivers in the smallest available flat pack they can get away with, so arguably Ricci's test method of using the same small box size for everything is pretty useful.

 

Calculated qtc won't work either.  If you sim the qtc and build that box and measure the qtc, these ultra high excursion drivers will measure a whole lot different qtc than simulated.  That's a fact.  The higher the normalized inductance the more chance you have of being further off the measured qtc vs simulated.  As normalized inductance goes up apparent motor strength (compared to what you would expect from the t/s parameters) goes down.

 

These two things alone make your proposed test method as useless as you clam the current test method is.  Ideally I'd like to see IB testing for all drivers but even that won't cover ALL the bases.



#35 Ricci

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Posted 08 April 2016 - 07:43 PM

Of course, you know I disagree with the notion that every driver has been optimally tested regarding excursion. This is only because readers split decibels as though they were truckloads of food in a world of starving people.

 

As I mentioned in the other thread, a small sealed box does several things, among which, being the most relevant on this subject, it induces asymmetrical (non-linear) excursion. This causes an increase in THD and changes excursion measurements.

 

There is no chance that mounting the XXX in 4 cubes vs in an IB will result in zero difference other than required input power.

 

Without an accurate means to measure excursion, you simply can't make that assumption. Anyone would have to agree that comments like; "It looked like the cone was moving about 25 mm in one direction...", "...mechanical noise set in" are absurdly inaccurate gauges for actual excursion behavior and distances.

 

In any case, my argument was not whether or not the driver was pushed to full excursion. It's the CEA 2010 number that matters, not the obscure no-THD-limit number. If the XXX excursion capability claims are anywhere near accurate, it should be capable of AT LEAST +3dB more output than the RF 19" driver. Instead, the results show the XXX giving -6dB less. That's a 9dB swing for a single driver.

 

To test a "DIY" driver (vs a commercial subwoofer "system"), each driver should be in a Vb that yields a calculated Qtc of .707. Otherwise, especially when comparing an extremely low Qts driver like the original LMS-Ultra-18" or RF-19" to the extremely high Qts RE-XXX, the CEA-2010 burst numbers are meaningless as a comparative tool.

 

Of course, that's not practical. Instead, there should be a calculator for HT eligibility that factors box size. There are enough program savvy readers out there who could whip that up toot suite if there was ever a discussion about the parameters instead of the go-zillion discussions about which driver posted higher CEA numbers.

 

Personally, I don't care either way. There are many more important factors in designing and building a subwoofer system for HT Than yakking over 3 mm of Klippel verified one-way throw. But, to dismiss the fact that every driver is tested in the same box by referring to a metric that I believe is all but useless begs a differing opinion.

 

I did not say that the tests were optimal regarding excursion. We all know that they are not due to the varying performance characteristics of each driver. What the tests do indicate is how each driver behaves when given the same amount of space to operate. In that way it is all comparable directly. Every driver has been pushed to its mechanical excursion limit. This is a fact you can choose to believe or not. The sound a long throw driver makes when it is about to have something bad happen mechanically has zero to do with THD or air spring distortion. It isn't a harmonic distortion. In some rare cases the drivers do not make obvious mechanical noises and they will break abruptly like the LMS or UXL. Saying that "mechanical noise occurred" is absolutely not an absurd comment. These are not subtle noises we are talking about here like listening for nuances in recordings between speakers. These are noises no speaker should ever make.

 

Your point about ASD is a good one and something that doesn't get discussed much. An interesting comparison is the SI 24 compared with the HST18. Unfortunately I don't have distortion measurements from the exact same voltages but it is easy to see that the 24 has far lower distortion than the 18, yet the distortion profiles and overall shape are quite similar. we know that the motors on the 2 drivers are very similar if not the same as is the coil. They are brothers at least if not twins. I believe the cause of the increased distortion levels on the HST, in the deep bass at least, have to do with the much smaller air space, 1/4 that of the 24 and the reduced efficiency requiring much more power through the coil which increases BL distortion. I believe that accounts for the increase in the upper bass range.

 

A general observation I have on distortion performance is that a stronger motor and lower qts, or lower system qtc results in less overall THD and likely lowers the effect of ASD too. The greater efficiency lowers the amount of power in the coil/motor and lowers BL distortion. I didn't say that there would be no difference at all between the XXX in 4 cubes versus 100 cubes other than the efficiency. Nearly everything will be different except for the excursion limited maximum output which was what was being discussed. The IB will have better efficiency, flatter response, better deep bass sensitivity, likely much lower deep bass distortion, less compression with long term signals, etc. Basically win across the board other than size. It will put up higher CEA-2010 distortion limited numbers in the deep bass as well. It will not have any greater maximum output in the deep bass. Once the driver is out of displacement it's done. It's not going to somehow put out 113dB at 20Hz if a 100cube cab was used. The cone cannot move that far. 111-111.5dB is it unless you want to chance breaking the thing and getting a re-cone. It may be able to eke out another 0.5dB before it dies, or not. I didn't want to chance it due to the "noises" it was making. Putting it in IB will absolutely drop the THD by a large amount so the CEA-2010 scores would go way up. It's not going to give the driver another 10mm of stroke though.

 

The burst scores are distortion limited. A lot of drivers fail well before even reaching the claimed xmax. Unless they do make it to the maximum excursion in the small 4 cube box like the LMS, they will see the numbers go up in the deep bass in IB. That's most of the drivers tested not just the XXX. How much is unknown. I do believe that drivers operating at a much higher qtc in the test box to begin with would see distortion drop more than those that are a lower qtc in the test box. So the XXX for example would see a greater distortion reduction and subsequent increase in the burst scores in the deep bass compared with the 19 for example which should also see an increase in the burst scores and reduction in THD but likely to a smaller degree since it is already much lower qtc to begin with.The 19 was about 2-3dB on average below it's maximum displacement with the burst scores from 10-25Hz. The XXX on the other hand varied greatly much like other high qtc, high inductance drivers and was not able to produce 10Hz very cleanly until well below it's displacement limits and xmax rating. A little closer at 12.5Hz, closer still at 16Hz and then once getting into the area of the impedance peak where efficiency is higher it comes close. Right at the maximum efficiency of the cab at 25-31.5Hz there is a dB or less difference between the THD limited burst output and the maximum before damage. This type of performance is common with the high inductance drivers. They do not like being driven below the system resonance and the distortion is much higher. If you look at the Max SPL limit in the red column for both drivers it shows that the 2 drivers are neck and neck as far as total displacement capability.

 

XXX SEAL 4.5 CU FT CEA2010.PNG

T3S2-19 SEALED CEA-2010.png

 

On paper going by just the xmax claims the XXX should have a bit over 2dB more output than the 19. The measurements show different and this goes back to some of the discussion on the ways xmax is stated and what that number is actually worth. The XXX claims 54mm and has an additional maybe 5 to 6mm before it breaks the spider triple joint on the motor top plate " volcano". It will move that far physically but calling 54mm a true xmax number is far fetched to say the least. Just looking at the surround and spiders on it immediately indicates that those are going to be bottlenecks and nowhere near linear at that much stroke even if the BL is (on the split coil). The surround is the real issue on it. It gets stretched tight well before then. A real world useful xmax on it would be maybe 40mm with a 55-60mm xmech. I've mentioned this same info a number of times over the years. Still has excursion well beyond most anything else up until a few years ago. The 19 is rated at 34mm xmax and has a bit more sd. On paper it has 2.5dB or so less displacement capability. Measurements show different. The 34mm spec is a genuine coil overhang spec with no adder. Coil winding height -Gap depth / 2. Most long throw drivers claiming this much excursion have nowhere near that much physical overhang or mathematical xmax.

The 19's 34mm xmax is a legit useable amount of excursion where the driver is still very linear with low distortion and no where near bottoming out. Plus it is Klippel verified. Hehe...The XXX's 54mm claim is not apples to apples at all as the driver is well into heavy suspension non linearity and huge distortion by that point with the mechanical limit just a few mm away. 40mm is far more realistic for it. The mechanical limit on the 19 is right around 47mm or perhaps even a bit more as far as I've been able to gauge it. The two drivers have near identical total displacement despite what any paper specs might say. You can't compare what amounts to a conservative xmax rating to another drivers xmech. This is exactly the type of thing that made me start doing the testing of drivers.

 

 



#36 lilmike

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Posted 08 April 2016 - 08:23 PM

"I haven't looked into the info in that post very carefully, perhaps I should.  But when it comes to reactive inductance, higher math and imaginary numbers, that's where the math goes above my head."

 

Join the club. I know enough about this stuff to recognize that I don't know nearly enough to fully understand it. 

 

I wish I had the time to experiment, measure, and learn more. Not likely any time soon.

 

"If you look for driver indications: high Le and/or high Mms (for its size) in relation to a low EBP value."

 

This is an interesting point. I may not have encountered this sort of deviation, because most of the drivers I have worked with aren't going to fall into that bin. The lowest EBP driver I have done any real work with lately is my Shiva X2, and it has a fairly low inductance and a low Mms. Though the CVX 15 has a higher Mms and is higher inductance, the inductance still normalized out to slightly over 1 mH/Ohm IIRC, and it has an EBP up over 80.

 

That may be changing soon. I haven't seen specs on my new driver yet. I anticipate EBP will fall between the two, but I should have some room before I reach saturation, so I can add a bit more B if needed. I expect that though Le will be mitigated to the degree possible given my budget, Le will still be higher than I'd like to see. I do hope that I can keep it below 1.0 mH/ohm though. Since it is an 18 with a long 4"/4 layer coil, I expect that Mms will be high enough to warrant applying your correction approach.

 

I also need to run your correction approach on a recent build that was an educational experience. I think I have a full understanding of what went wrong and why, but it does warrant a quick check, and the sim's already in HR. 

 

"So I have no idea why it works or why it's even necessary for this type of driver.  But it does work."

 

I get it. Thanks for the explanation, I really do appreciate your effort.

 

I'm just trying to understand the "why" behind the observations because it is my nature, sometimes my questions can come across as more than I intend them to be.



#37 diy speaker guy

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Posted 08 April 2016 - 10:15 PM



 

"If you look for driver indications: high Le and/or high Mms (for its size) in relation to a low EBP value."

 

This is an interesting point. I may not have encountered this sort of deviation, because most of the drivers I have worked with aren't going to fall into that bin. The lowest EBP driver I have done any real work with lately is my Shiva X2, and it has a fairly low inductance and a low Mms. Though the CVX 15 has a higher Mms and is higher inductance, the inductance still normalized out to slightly over 1 mH/Ohm IIRC, and it has an EBP up over 80.

 

That may be changing soon. I haven't seen specs on my new driver yet. I anticipate EBP will fall between the two, but I should have some room before I reach saturation, so I can add a bit more B if needed. I expect that though Le will be mitigated to the degree possible given my budget, Le will still be higher than I'd like to see. I do hope that I can keep it below 1.0 mH/ohm though. Since it is an 18 with a long 4"/4 layer coil, I expect that Mms will be high enough to warrant applying your correction approach.

 

I should have spent some time going over his chart and relating the Le Mms and EBP.  It would have been a lot easier if he laid his chart out like I did, by normalized inductance (Le/Re low to high) instead of alphabetically.

 

His chart looks at a lot of things I never did - Mms, normalized Bl (Bl2 / Re), EBP, and he didn't look at normalized inductance at all.  Inductance has to be normalized of course, Le means nothing without Re.  If Le is 4 and Re is 2, that's incredibly high inductance.  But if Le is 4 and Re is 16 that's very low inductance.

 

I latched onto Re as an adjustment right away, because looking at data-bass measurements and comparing to simple sims qtc was obviously higher than expected in the measurements, and I'd seen that before, when I add Re to a sim.  So I was always laser focused on the two parameters that electrically raise qtc - Re and then later Bl.  I never even thought to look at relative Mms, normalized Bl or EBP, so I have no idea if his statement "If you look for driver indications: high Le and/or high Mms (for its size) in relation to a low EBP value. " is going to pan out under close scrutiny or not.

 

But as my normalized inductance vs % Bl adjustment scatter graph shows clearly, there is a trend between the amount of normalized inductance and the amount of Bl that will make the sim match the measurement.  I'm pretty sure there is an even more accurate way to tweak than my method but I couldn't justify more than a few weeks on the study and didn't know what to look at next.

 

 

 

NOW - if I was going to design a multi thousand dollar horn with this type of driver here's how I would do it, and this is what I would recommend to you.  (I would NOT use the generic formula, as you can see on the scatter graph there are outliers, if your driver is an outlier your results won't be as accurate as they could be.  The generic formula is an "easy button" for people that can't or don't want to do what I suggest here.)

 

Get the driver in hand.

Measure t/s parameters, both cold and warm.

Put the driver in a sealed box.

Measure FR, both cold and warm.

Sim the box you just measured with measured t/s parameters.

Adjust Bl until the sim matches the measurement (you will notice that sensitivity will be a couple db low in the sim but the curve shape will match really well once Bl is adjusted.)

Use that Bl value for the subsequent sims to design the horn.

Come up with a sim you like for the project.

 

These next steps are not 100 percent necessary but they should eliminate any concern over the adjustment method being less than perfect, just a little additional insurance and it doesn't cost anything but time.

Sim the horn with the cold AND the hot measured t/s without any adjustment.

Sim the horn with the cold AND hot measured t/s WITH the Bl adjustment.

If all 4 of these sims provide a usable performance envelope in the same horn then it's almost guaranteed not to fail, I don't see how the final product could possibly turn out bad.

These 4 sims will be quite different, the cold t/s without adjustment in particular will be vastly different than the hot t/s with Bl adjustment, but it should just be a matter of one being much more damped than the other and the low knee will shift a bit.  The measured performance of the finished product will very likely fall somewhere in between these two extremes and if you measure the finished product with the driver cold it should match your adjusted cold driver sim pretty well.

AND since you have already simulated the worst case scenario from a box size perspective (sim with hot t/s parameters with the Bl adjustment) you know for a fact that the box will be big enough, even with a bit of power compression thrown in the mix.

 

This is a lot of extra steps, but it's what I would do considering it's free to play with sims and building a multi thousand dollar horn costs several thousand dollars.  I do trust the method but it's in my nature to go the extra mile to ensure success.  The wide range of conditions that these extra 4 sims will provide should guarantee success beyond any doubt and satisfy everyone from the person that doesn't trust the method to the persona that is overly worried about power compression.  If you can get all 4 of these simulated scenarios to sim well in your horn I don't see how it could possibly fail.


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#38 lilmike

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Posted 11 April 2016 - 08:15 PM

Well, step one will be measuring things, that's a given. I really prefer measuring the Vas of larger drivers with a test box, so I'll have a small sealed cabinet on hand anyhow. 

 

I'll see what I've got to work with when I get the driver in hand. Thanks for the detailed explanation of how you'd approach things.

 

I did try the large coil option on my Shiva model. Though there is a shift that is sort of in like with what I measured, it doesn't explain all of what I observed. My other experiments suggest a more obvious explanation for my results. Oh well, I turned a sheet of ply into fancy firewood, but I hopefully learn some things in the process. Not the first time, and certainly won't be the last. 



#39 MKtheater

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Posted 11 April 2016 - 09:22 PM

Ricci, on your measurements comparison you have the xxx hitting 96 and 97 dB max, not 99.  Either way for $850 it was a great value, the mid bass lacked though compared to others now, like your 19(much more expensive) and the 24.



#40 Ricci

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Posted 12 April 2016 - 01:05 AM

Ricci, on your measurements comparison you have the xxx hitting 96 and 97 dB max, not 99.  Either way for $850 it was a great value, the mid bass lacked though compared to others now, like your 19(much more expensive) and the 24.

 

James,

CEA-2010 is not always maximum burst output. It can be but seldom is in the deep bass. Please read the post above and look at the burst charts provided for each driver. ;)






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