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Old 1st August 2007, 03:20 AM   #81
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Quote:
Originally posted by CeramicMan


One possible answer: Curve fitting.

Another possibility: a DC offset before the start of the impulse, or after it finishes

No need to these, P18's FR curve in that region is noticeably smoother than L18, you just need to know what to look for. The CSD results are no suprise, I posted on this above with the details. That is a reason why CSD can be useful, it is visually easier to see those. But they are also already in the FR of the drivers.
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Old 1st August 2007, 03:32 AM   #82
PB2 is offline PB2  United States
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Default Re: Re: Re: There's little agreement as to which is best

Quote:
Originally posted by dlr


My comments never related to those drivers, I responded to specific erroneous statements that are proveaby false. I will be posting at my site, after I have time to finish the work, empirical proof that hard cone resonance peaks can indeed be absolutely controlled. Would one do that with all of them? No. Could that be done? Yes. Is that practical? No, not without DSP. But the fact that they can be is the topic of the discussion here. I will also do small signal and large signal measurements, though I don't plan on doing any compression tests requiring significant voice coil heating.

I have also, for many, many years, used CALSOD to recreate with fine detail every single tiny peak in a measurement up to 20KHz, even in large drivers, and have that mode used to generate the Hilbert-Bode phase. The phase thus generated matches precisely the measured phase. Raw drivers, with rare exception, are minimum-phase devices. They can be modified with a crossover that has a minimum-phase transfer response that can and will result in a minimum-phase driver response for the correction of non-linearities. Were that not so, CAD software for speaker design would not work.

Coincidentally, I was recently reading for the first time an AES article on CALSOD presented by the designer that included reference to the minimum-phase nature of raw drivers. To quote:



See "Simulation and Optimization of Multiway Loudspeaker System Using a Person Computer", by Witold Waldman, Audio Engineering Society, September 1988. I'll leave it to you to research in more detail if you care. As for me, I know that they are minimum-phase devices. That's no speculation on my part. I have gone well beyond the "working range" and modeled raw driver FR up to 22KHz in fine detail. They are still minimum-phase. CALSOD uses minimum-phase elements as the fundamental building block for creating a CAD model of FR response from which the H-B phase is generated. There is never any disagreement between measured and modeled phase up to the limit. It is a time consuming task, but I have done that on several occasions over the years.



No, I think not as well. But handling that is part of the art of speaker design.

That was just not what was at issue. What was at issue was whether or not it was even possible. That should no longer be at issue. I will be following up over the next few days, over the weekend I hope, with a post of some initial measurements that directly support my points. I've been listening to a set of speakers with a peaky driver for a few weeks now, but I'm continually refining the crossover. Fortunately, I have SoundEasy and can use it's Digital Filter mode and not have to construct a physical crossover, though I will once I've finalized it.



Can't disagree in large part. All drivers have breakup, thus all drivers are compromises in the bandpass and the stopband, soft as well as hard.



One notch very well might, it's case dependent. But the claim was related to possibility, not practicality. Even so, the posting of a crossover for the said peaky driver is "good enough" in the stop band. You may be surprised at just how insignificant the higher mode resonances will be. I'll even post CSD graphs!!!!!



Here I believe it is you who may be using conjecture and are in error. It is valid for the FR linear system characteristic. Even so, as I pointed out, ALL drivers have non-LTI characteristics. I'm puzzled as to why you have formed this opinion. Years of AES papers, the least of which is the one quoted, contradict that, I believe. The typical driver is a minimum-phase device. The motor non-linearity is an issue, but it's primarily the motor, not the diaphragm material, that is the culprit. That exists in all motors. It is easily demonstrated in the distortion measurements, by far the best way to analyze a driver for this influence. But that does not alter the linear response characteristics that are LTI. The linear distortion of the diaphragm does influence the amplification of the nonlinear motor influences, yes, but the linear FR is fully minimum-phase. We do need to be more precise if this level of detail is to be debated.



This is probably the misunderstanding between us. I do not claim that nonlinear distortion can be equalized, never have, never will. I do claim that the FR nonlinearities that are linear functions can be equalized and I will be providing fully documented emprical proof when I finish the crossover and can write up the page to post at my site. I had planned on this only for presenting a possible crossover redesign for a system that I recently purchased, but it will serve this purpose well in addition.

Now are any drivers absolutely LTI? No, none are. Are they reasonably so? Yes. Of course one of the factors between drivers is, indirectly, how close to LTI are they? The better drivers have better heat dissipation thus lower compression thus are closer to LTI. Drivers with better motors likely have copper clad voice coil gaps that mitigate dynamic gap Bl modulation (if I've got the term correct), that helps to making it LTI. But in most cases, practically all, the design issues related to this are generally not associated with the breakup and driver FR nonlinearities, it is the low level T/S parameters that used in the box design, though it will affect the driver across the board to one extent or another and choosing the driver for the target that best fits, including distortion considerations when that data is available. Also, not many folks have access to a Klippel system or similar to assist with a higher signal level design. Certainly most who may read this do not, I believe. But the T/S parameters, though they can be highly affected by heat compression, still are used and still are fairly reliable for system design.



I believe that for practical purposes, all typical drivers a reasonably "soft" as you say. Certainly so for the FR linear characteristics. CAD models would break down for drivers that don't exhibit this, but in fact, essentially all drivers can be modeled for FR very accurately due to their minimum-phase nature.



I'm sure that zaph would be much better at addressing this than I.

Just as I was about to post I saw Feyz' post, but I'm not going to edit mine. If you has data correcting anything in mine, I thank him for posting.

Dave

[/QUOTE]


You've spent a lot of words there stating that drivers are minimum phase, yeah I know that, most are. I only stated it as a requirement to be complete in my statements. I don't think I ever said anything but that it was a requirement.

The claim at the start was that the L18 with 7 peaks in it's response could be made to perform as well, even better than the P18 through linear EQ. You don't need to provide any proof that you can EQ the FR, I get that, it is very basic. My point is that you cannot simply treat just the linear case without also considering the non-linear aspects of the driver.

I'm not concerned with where the distortion originates in metal cone drivers, the fact is that it is significantly higher and no amount of linear EQ in the crossover will correct it, and make it the same as a driver with less distortion which is what was suggested at the start of this thread.

What I take issue with regarding your view of the matter is that you think you can just look at the linear aspects of a system and ignore the non-linear.

What I see many saying here is that if you let us pretend that the system is linear then this theorem is valid, but the fact is that the system is not very linear and so you cannot make such forceful and rigorous claims. I'm bowing out now thanks.

Pete B.
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Old 1st August 2007, 03:46 AM   #83
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Default Re: Re: Re: Re: There's little agreement as to which is best

Quote:
Originally posted by PB2
What I see many saying here is that if you let us pretend that the system is linear then this theorem is valid, but the fact is that the system is not very linear and so you cannot make such forceful and rigorous claims. I'm bowing out now thanks.

Pete B. [/B][/QUOTE]

Sorry but the start of the thread was about the CSD differences of two drivers, and a response to it saying the CSD is directly related to the FR of the drivers. When talking about FR, CSD, it is already assumed that the driver is linear. Whether or not it is really linear, or how much linear is irrelevant, because these already presume that the system is linear. And since this is already presumed, there is nothing wrong bringing the point that if FR irregularities are corrected the CSD and time response will be correct as well. Your point that drivers are nonlinear so they can't be corrected completely is valid, but irrelevant in this discussion.
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Old 1st August 2007, 04:02 AM   #84
ucla88 is offline ucla88  Tahiti
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Hi Pete,

I know we seem to be talking past each other. If so, then my comments are for others.

But you're having trouble clearly distinguishing between linear and nonlinear distortion.

Linear distortion is just amplitude distortion and can be corrected.

Nonlinear distortion is an entirely different phenomena and is dominated by the motor and excursion. Nonlinear distortion cannot be equalized, or at least not easily. (servo feedback, etc. There are ways of eq'ing or mitigating NL distortion)

However, directly connecting the amplitude of cone breakup and nonlinear distortion is incorrect.

Cone breakup may be responsible for some nonlinearities and in fact this can be measured. But it is not the dominant factor in nonlinear distortion.

If you're talking about nonlinear phenomena, you cannot make the assumption that "soft breakup" of a paper dome over a wide frequency range has less nonlinear distortion than "hard breakup" associated with a metal cone. You are mixing the amplitude distortion (read, linear distortion) with any nonlinear phenomena.

There has been no experimental data on nonlinear distortion and cone breakup presented anywhere in this thread. I've actually been trying to use some close thirds measurements to see if I can find any experimental correlation of breakup and nonlinear distortion. This would not show in a CSD. More on that someday, when I have time. Still, it seems that the low end/excursion dominates.

It is an error to assume more severe linear distortion implies more severe nonlinear distortion.

Many metal cones have clearly better nonlinear distortion than their paper counterparts. Look at the Seas datasheets for the metal and non metal seas drivers. It is quite clear that the metal cones have better nonlinear numbers, regardless of their fr/csd.

edit-didn't see Feyz' post. He said the same more succinctly...
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Old 1st August 2007, 04:09 AM   #85
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Default Some perspective

To give some perspective, assume the driver distorts 20% on AVERAGE (which is a very bad driver) while playing music. 20% distortion means the distortion is -14 db lower than the signal generated. -14db error while doing frequency response correction or shaping is acceptable. I know this is a simplification, but at least gives some perspective, that attempting to correct FR anamolies of drivers are not a futile attempt just because the drivers are nonlinear. I would be more worried about messing up the off axis response while correcting the on axis than the nonlinearity of the driver messing up the equalization.
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Old 1st August 2007, 05:20 AM   #86
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Quote:
Originally posted by Feyz


No need to these, P18's FR curve in that region is noticeably smoother than L18, you just need to know what to look for. The CSD results are no suprise, I posted on this above with the details. That is a reason why CSD can be useful, it is visually easier to see those. But they are also already in the FR of the drivers.
Well, there must be some form of curve fitting used in the graph, otherwise there would be large regions of empty space between isolated dots in the vicinity of 1500, 1800, 2100, 2400, 2700... etc Hz.

Both CSD graphs display a response increase when approaching 15kHz~20kHz, which is not present in the original FR plots. This suggests either a problem with shape of the sliding windows, or the total sampling period was too short, or both. The sliding windows could also have different widths, making the L18 response appear to be "sustained" longer for no apparent reason.
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Old 1st August 2007, 05:47 AM   #87
PB2 is offline PB2  United States
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Default Re: Re: Re: Re: Re: There's little agreement as to which is best

Quote:
Originally posted by Feyz


Sorry but the start of the thread was about the CSD differences of two drivers, and a response to it saying the CSD is directly related to the FR of the drivers. When talking about FR, CSD, it is already assumed that the driver is linear. Whether or not it is really linear, or how much linear is irrelevant, because these already presume that the system is linear. And since this is already presumed, there is nothing wrong bringing the point that if FR irregularities are corrected the CSD and time response will be correct as well. Your point that drivers are nonlinear so they can't be corrected completely is valid, but irrelevant in this discussion.
Look try to be certain that what you write and claim is accurate, a few people concentrated on the CSD, and you seem fixated on it, and the fact that once again you think you can assume a linear system just because it is "presumed". So reality doesn't matter just that we all stick to you're chosen presumptions which make you correct? I was trying to give the group a reality check!

This is the first post and how the thread started, much more than CSD:

"Curious about ZAPH's designs. Seas L18 and P18RNXP Post #1
Having NO knowledge in speaker design, I'm doing alot of reading and trying to get a better understanding of what makes a good driver (among other things). I was looking at Zaph's L18 design and looking at his 6.5" measurements and comparison... And can't help but wonder why did he choose the L18 over the P18RNXP?

If I look at the responce curve and the harmonic distortion, They are very comparable (to me). But when I look at the SCD graph, the P18RNXP looks like a clear winner. What am I not understanding or overlooking?"

Seems he asked about a lot of things and wants a basic understanding.

Pete B.
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Old 1st August 2007, 09:13 AM   #88
sreten is offline sreten  United Kingdom
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Quote:
: from Zaph's article
The midrange has a certain transparency that I love and I'm only
able to obtain with stiff metal cones and a good system design.
Hi,

Well the above answers the basic question, pistonic cone behaviour
to well beyond the c/o point, which cannot be done with "soft" drivers.

"Soft" drivers of this size enter break up mode between 1KHz and 2kHz.

You pay your money and you take your choice : "perfect" midband
but some emphasis of distortion, to "very good" midband with no
emphasis of distortion.

Peoples opinions of the above may vary, but its Zaph's perogative
to build the speakers the way he wants to, you go along with his
methodology or not. It is not a philosophical question, the L18
design is one of the best all metal cone designs available, if you
do not like metal cone designs leave it, if you do consider it ....

I do not think a particular metal cone design should have to defend
the whole metal vs plastic vs paper vs textile debate. Seas do not
bother with such questions either, they simply give the customer
pretty good versions of what they want for various technologies.

/sreten.
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Old 1st August 2007, 11:45 AM   #89
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Quote:
Originally posted by CeramicMan


Well, there must be some form of curve fitting used in the graph, otherwise there would be large regions of empty space between isolated dots in the vicinity of 1500, 1800, 2100, 2400, 2700... etc Hz.
The space between those points are my guess is filled by using a longer FFT size.

But, the point is just by looking at the two FR curves of the two drivers, to my eyes, I can easily say that P18 is a better choice in terms of linear distortion (FR and time) in the region below 3Khz. Because L18's FR curve is more wiggley (for the lack of a better term) at that region and P18's is smoother in contrast. And CSD just relays that information also.

You are right the CSD window used at start must be different than the ones used at FR generation, and that makes CSD more suspect.

What I am really trying to say is, there is no magical energy storage property of the drivers that doesn't already show themselves on a high resolution FR graph. What tools, graphs one uses to detect or display them is a choice.
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Old 1st August 2007, 12:16 PM   #90
dlr is offline dlr  United States
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Default Re: Re: Re: Re: There's little agreement as to which is best

Quote:
Originally posted by PB2 You've spent a lot of words there stating that drivers are minimum phase, yeah I know that, most are. I only stated it as a requirement to be complete in my statements. I don't think I ever said anything but that it was a requirement.
Don't presume that every word written at a board is for your edification alone. Lack of precision and thoroughness tends to leave things such that misinterpretation results. That may be the case here to some degree and I think that I may see why we're going around in circles.

Quote:
The claim at the start was that the L18 with 7 peaks in it's response could be made to perform as well, even better than the P18 through linear EQ. You don't need to provide any proof that you can EQ the FR, I get that, it is very basic. My point is that you cannot simply treat just the linear case without also considering the non-linear aspects of the driver.
I have not addressed the question directly about the two drivers. Others have, I see no node for me to do so. I have not heard them, others have, zaph in particular. His first post was probably the most direct, correct and useful post in this whole thread as a response to the original poster. Unfortunately, it took the downturn with other posts that had not only misleading but bad information. That should be abundantly clear now.

Quote:
I'm not concerned with where the distortion originates in metal cone drivers, the fact is that it is significantly higher and no amount of linear EQ in the crossover will correct it, and make it the same as a driver with less distortion which is what was suggested at the start of this thread.
No, you are now stating your conjecture. Based on those who have made extensive measurements as well as the manufacturers data shows that for the same motor, the nonlinear distortion will actually be higher for softer diaphragms in the passband, though it can vary due to different amplification from the linear distortion characteristic differences between cones. What this means and what has remained unchanged is that it is up to the designer to select an appropriate driver for the task. The impact of where the distortion enters into must be known for an optimum design, since optimum is all one can approach and what's optimum for one person is not necessary the same for the next person.

Consider a midrange. Nonlinear distortion is largely related to displacement. If I want to minimize that component, one way is to use a somewhat higher highpass Fc to lower the displacement in the final design. For a woofer I could do the same, sacrificing a bit of extension. But in the end it's all a choice of the designer. You cannot tell me with any credibility what the final distortion characteristics will be present in any design until that design is complete. The linear distortion corrections made by the crossover have a direct and significant impact on that result. There is no absolute with raw drivers because of this.

Some drivers may have very good low levels of distortion until they have significant displacement. If one does it right, even small amounts of Fc change could have a strong impact on the final distortion characteristics. So the linear and the nonlinear tied in that fashion, but they are separate in others, one being the ability to use CAD software to control the linear aspect directly.

Quote:
What I take issue with regarding your view of the matter is that you think you can just look at the linear aspects of a system and ignore the non-linear.
I never said that and if you had paid more attention to my earlier posts you would know my position on this. I separated the two because the original thread veered off into parts with one being on the absolutes of a CSD vs. FR. Even within that sub-thread, so-to-speak, I pointed out specifically the issue of the nonlinear distortion impact, but did not care to go down that path as the discussion was focused on the linear distortions.

Quote:
What I see many saying here is that if you let us pretend that the system is linear then this theorem is valid, but the fact is that the system is not very linear and so you cannot make such forceful and rigorous claims. I'm bowing out now thanks.
We are not pretending. We are discussing the same as those who originally postulated the case for computer modeling and then implemented software that, as others here have explained quite clearly, must rely on the system as being LTI. The nonlinear aspect is then examined through measurements that cannot be determined by the CSD nor the FR. The designer then tries to use his own brain to use both sets of data to make his decisions on choice of drivers, then on where and how to cross. Some may to it vice-versa, that doesn't matter. In the end, the final distortion characteristics can still only be known through subsequent measurements.

The drivers are far more linear than you realize. Were that not the case, none of the CAD software used for many years would not work as they rely on that fact. They do not address directly the nonlinear influences in the drivers, that part is true, but that's what the designer does separately. It's a process and to some degree still an art. That's part of what makes speaker design an interesting hobby for many.

Dave
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