Danny,
Please post the impulse response and window information. The first measurement appears to suffer from a severe reflection, internal or external. I have to agree with Dave that the measurements, especially the first is of very poor quality. Hard to make much of this.
I would avoid boasting this is industry standard...
I'll comment if I see some hiqh quality measurements. However, short windowed, smoothed, or measurements contaminated with reflections don't have much merit.
Please post the impulse response and window information. The first measurement appears to suffer from a severe reflection, internal or external. I have to agree with Dave that the measurements, especially the first is of very poor quality. Hard to make much of this.
I would avoid boasting this is industry standard...
I'll comment if I see some hiqh quality measurements. However, short windowed, smoothed, or measurements contaminated with reflections don't have much merit.
I'll throw some very old measurements out for others to look at-mainly because they're already done and sitting on an old website already
Which has more stored energy? Duh, trick question. Just different windows...
Another one
Which has the most stored energy. Ha, another trick question.
Yet another one
Anyway, the point is that some more thought has to go into measurements than you are offering. The impulse, the measurement conditions, the window, in box, out of box, stuffing, etc.
Showing a measurement with a baffle difraction or internal reflection etc is not very helpful. You have to look at the inherent FR/impulse response of the driver and take care to eliminate baffle, box, or other extradriver reflections.
Again, looking at a short windowed 1m measurement in a box and trying to glean the inherent FR/stored energy properties of a driver is fraught with error.
An externally hosted image should be here but it was not working when we last tested it.
Which has more stored energy? Duh, trick question. Just different windows...
Another one
An externally hosted image should be here but it was not working when we last tested it.
Which has the most stored energy. Ha, another trick question.
Yet another one
An externally hosted image should be here but it was not working when we last tested it.
Anyway, the point is that some more thought has to go into measurements than you are offering. The impulse, the measurement conditions, the window, in box, out of box, stuffing, etc.
Showing a measurement with a baffle difraction or internal reflection etc is not very helpful. You have to look at the inherent FR/impulse response of the driver and take care to eliminate baffle, box, or other extradriver reflections.
Again, looking at a short windowed 1m measurement in a box and trying to glean the inherent FR/stored energy properties of a driver is fraught with error.
Time window is clearly stated on the measurements just like yours is.
Now if I posted the impulse response that would be useful, but the claim was that one can predict the CSD only from the frequency response.
Like trying to predict the CSD from the frequency response, that would be a predictable guess, but not correct.
As I already mentioned, "Both mounted in the same box (9" wide and 14" tall)." They had the same damping material too.
Yet, they are just like yours. You started your time window just before the arrival of the impulse response and gated it right before your first room reflection.
They are the same as your measurements (except I used higher resolution. Mine is on a 5db scale, yours is on a 10db scale), same time window, NOT smoothed, and have no reflections other than what can reflect off of a small enclosure (enclosure surface area already stated).
Well it appears that you are using a Clio system since your measurements are posted using a Clio system, so I would think that you'd be able to see the clearly posted time window and know that it is NOT 1ms long. That would be pretty foolish would it not?
No, not contaminated. Made the same. You are going to eventually use the woofer in a box are you not? How better to measure a woofer than in the box it will be used in?
PS
I missed the part about two woofers. Now it gets evey more complex. The FR curve also depends on baffle geometry and electrical hookup. Of course, so does the CSD, since they're both generated from the same impulse. However, it's hard to look at a driver's inherent linearity with two of them on a baffle...
I missed the part about two woofers. Now it gets evey more complex. The FR curve also depends on baffle geometry and electrical hookup. Of course, so does the CSD, since they're both generated from the same impulse. However, it's hard to look at a driver's inherent linearity with two of them on a baffle...
Danny said:
So why take gated measurements when comparing woofers. They are both in the same room, right? No need to use calibrated microphones either, since they will affect both woofers the same.
If the measurement would be used to design a crossover, I agree you should take in-box measurements. I do not agree with you if the measurement is used to compare drivers.
Dan
Man, I am amazed. Even when I pick two 8" woofers that are completely different and have obvious stored energy differences you guys are still afraid to step up to the plate.
All of you guys that stated you could read all the CSD info just from a frequency response were all no shows.
I will agree that those with experience will get a good idea of the stored energy problems by looking at a frequency response and the impulse response. You can see an area of break up and have a really good idea of the stored energy that might be there.
Dave, Mark, Pete, and myself can easily see this, but not everyone.
However, we can't see how much stored energy, how long, or how bad until we look at the CSD.
Further more, to suggest to a bunch of hobbyist that CSD info is of no value is ridiculous and misleading.
The following will easily illustrate what I have just stated.
Let's look at those two 8" woofers again. Here is the first one:
This was an Alpha A from Eminence. It is a fairly light weight paper cone with corrugated cloth suspension. Here is the spectral decay:
In order to keep its output level close to the other woofer tested I only sent it about 1/2 of a watt.
I wish I would have saved this file but I did not. The impulse response looked very typical. I started the time window just before the arrival of the signal. It peaked and settled in about 3ms of total time. Then the impulse response was a flat line until the first room reflections that arrived at about 8ms. So I gated it out leaving a clean 5ms range.
Here is the second 8" woofers frequency response.
Sure, there are some serious clues there aren't there? It even has so much mass that it will hardly even play past the peak at 1kHz. What we can't see though is how much stored energy is there. How bad is it?
Let's see:
Not too good huh?
Now keep in mind that this woofer was played to nearly the same level as the other woofer. I think someone said that if two woofers are playing the same output level they will have the same stored energy. Well that is not true at all.
To play at this level this woofer had so much stored energy that the 5ms time window isn't even near long enough to catch it all.
Looking at its impulse response is like looking at one long curvy wave that just keeps on going. You couldn't even tell where the first room reflections were because the stored energy went right past it.
This woofer was also a paper cone woofer but is only used as a sub woofer. To get it to play to the same output level as the Alpha 8 with only 1/2 of a watt on it, this one needed the gain on the amp cranked up to a 100 watt level.
Yep, it needed 100 watts of input to give it the same output.
Differences in stored energy even below 1khz was tremendous.
And for those who will want to claim that the CSD is not accurate below 1kHz can take a reality check here. It may not be completely accurate but who cares. +/-1/4 or 1/2 of a db is nothing. Differences are in such magnitude that we easily see them.
I couldn't have pick two drivers more different, and still no one would comment. Amazing...
All of you guys that stated you could read all the CSD info just from a frequency response were all no shows.
I will agree that those with experience will get a good idea of the stored energy problems by looking at a frequency response and the impulse response. You can see an area of break up and have a really good idea of the stored energy that might be there.
Dave, Mark, Pete, and myself can easily see this, but not everyone.
However, we can't see how much stored energy, how long, or how bad until we look at the CSD.
Further more, to suggest to a bunch of hobbyist that CSD info is of no value is ridiculous and misleading.
The following will easily illustrate what I have just stated.
Let's look at those two 8" woofers again. Here is the first one:
An externally hosted image should be here but it was not working when we last tested it.
This was an Alpha A from Eminence. It is a fairly light weight paper cone with corrugated cloth suspension. Here is the spectral decay:
An externally hosted image should be here but it was not working when we last tested it.
In order to keep its output level close to the other woofer tested I only sent it about 1/2 of a watt.
I wish I would have saved this file but I did not. The impulse response looked very typical. I started the time window just before the arrival of the signal. It peaked and settled in about 3ms of total time. Then the impulse response was a flat line until the first room reflections that arrived at about 8ms. So I gated it out leaving a clean 5ms range.
Here is the second 8" woofers frequency response.
An externally hosted image should be here but it was not working when we last tested it.
Sure, there are some serious clues there aren't there? It even has so much mass that it will hardly even play past the peak at 1kHz. What we can't see though is how much stored energy is there. How bad is it?
Let's see:
An externally hosted image should be here but it was not working when we last tested it.
Not too good huh?
Now keep in mind that this woofer was played to nearly the same level as the other woofer. I think someone said that if two woofers are playing the same output level they will have the same stored energy. Well that is not true at all.
To play at this level this woofer had so much stored energy that the 5ms time window isn't even near long enough to catch it all.
Looking at its impulse response is like looking at one long curvy wave that just keeps on going. You couldn't even tell where the first room reflections were because the stored energy went right past it.
This woofer was also a paper cone woofer but is only used as a sub woofer. To get it to play to the same output level as the Alpha 8 with only 1/2 of a watt on it, this one needed the gain on the amp cranked up to a 100 watt level.
Yep, it needed 100 watts of input to give it the same output.
Differences in stored energy even below 1khz was tremendous.
And for those who will want to claim that the CSD is not accurate below 1kHz can take a reality check here. It may not be completely accurate but who cares. +/-1/4 or 1/2 of a db is nothing. Differences are in such magnitude that we easily see them.
I couldn't have pick two drivers more different, and still no one would comment. Amazing...
Hi,
I think the original post stated that CSD's could be misunderstood
and were not particularly needed with comparable drivers if you
knew what to look for in the frequency response.
Those that cannot read the frequency response are also the most
likely to misinterpret the CSD's, especially say when comparing
very similar overall performance "soft" (plastic) and "hard" (metal)
cone drivers.
I think the original statement that CSDs are next to useless has
to be taken in the correct context - of publishing comparative
test data - and the fact they are not much use to an amateur
designer in terms of the design process - which is frequency
response based - but they may be misinterpreted.
I do not think CSD's were being dismissed out of hand,
just they have to be interpreted correctly in context.
/sreten.
I think the original post stated that CSD's could be misunderstood
and were not particularly needed with comparable drivers if you
knew what to look for in the frequency response.
Those that cannot read the frequency response are also the most
likely to misinterpret the CSD's, especially say when comparing
very similar overall performance "soft" (plastic) and "hard" (metal)
cone drivers.
I think the original statement that CSDs are next to useless has
to be taken in the correct context - of publishing comparative
test data - and the fact they are not much use to an amateur
designer in terms of the design process - which is frequency
response based - but they may be misinterpreted.
I do not think CSD's were being dismissed out of hand,
just they have to be interpreted correctly in context.
/sreten.I had planned to drop this, but...
Before anyone brings up first order approximations, please keep in mind that this hijacked thread so-to-speak is at the point of focusing on the FR and CSD for a given drive level. This perforce means that they are generated from the same impulse response, so any comments about drive level nonlinearities are a separate issue. Valid, but separate.
The CSD is as subject to error as is the FR, maybe more so due to the successively shorter windows used to generate the decay. In any case, the "amount" is a nebulous term that you absolutely refuse to define. Not surprising, as there IS no absolute measure of reference for it, especially since it subject to the same or more vaguaries as is the FR. But all of it is reflected in the FR. Knowledge of some nebulous "how much stored energy" is useless. Useless Useless. Did I say useless? That would mean that one can do all that is required to design without the CSD. Yes, useless.
Why? Because there is no use in a CSD, the energy storage is clearly evident in the FR and all one need do is either compensate for it in the crossover or move on to the next driver. There is nothing in the CSD that gives additional information as to whether or not a compensation network can mitigate. Nothing.
Again, the CSD is useless. All it is good for is showing the neophyte that, yes, indeed, the raw driver has a set of various resonances of some magnitude and Q. Period. It does nothing else. Emphasis on the CSD is misdirected.
No, it's the absolute truth because whether experienced or not, the CSD provides NO additional USEFUL information that one needs to design. Nothing. Any and all non-linearities that are the result of the resonances are in the FR and include step and diffraction for that measurement position. One need ONLY the FR, coupled with distortion data if available and the impedance to determine and design.
Please direct us to this quote. I'm not aware of anyone making such a blanket statement. This is a specious argument put this way and I believe untrue. Use the direct quote for clarity if there is such. I don't think that you'll find it.
This is so clearly evident in the FR that it would be wasted time inspecting the CSD. Yes, again, useless to look at the CSD.
If this is the same setup as the others it's useless to try to determine the driver's response below 1KHz, or anywhere for that matter, with contaminated data. You've got the same 2.88ms start and a 7.85ms stop. I'm sorry, this is just lame.
All of which is evidence that if the user cannot properly set up a measurement to exclude reflections, it's the error of the person making the measurement. Contaminated data proves nothing. It's a simple task in such a case to find the proper point for the marker. One would assume that the measurement conditions are under control. This is a strawman argument if ever there was one. This is the same baseless kind of argument that you used in the beginning, using purposely contaminated data. It simply undermines your position.
The errors can be and often are much larger. They could easily swing +/- 5db, but in any case it's a limit of the window used. You can't seriously be arguing that a 3ms window of an impulse is valid? Ridges can appear or disappear depending on the users ability and even with small changes in the window length. In any case, there is not enough data below that point to be considered accurate given the short time samples of the examples.
We've all commented, only it's been to point out the serious shortcoming of your argument.
Here is a direct quote from your first post taking us to task:
This is an absolute statement, no equivocation. Do you stand by this? Let's have no equivocating now, yes or no, do you stand by this statement that you said previously or not?
Another quote from that first post:
[QUOTE
Danny said:
Before anyone brings up first order approximations, please keep in mind that this hijacked thread so-to-speak is at the point of focusing on the FR and CSD for a given drive level. This perforce means that they are generated from the same impulse response, so any comments about drive level nonlinearities are a separate issue. Valid, but separate.
The CSD is as subject to error as is the FR, maybe more so due to the successively shorter windows used to generate the decay. In any case, the "amount" is a nebulous term that you absolutely refuse to define. Not surprising, as there IS no absolute measure of reference for it, especially since it subject to the same or more vaguaries as is the FR. But all of it is reflected in the FR. Knowledge of some nebulous "how much stored energy" is useless. Useless Useless. Did I say useless? That would mean that one can do all that is required to design without the CSD. Yes, useless.
Why? Because there is no use in a CSD, the energy storage is clearly evident in the FR and all one need do is either compensate for it in the crossover or move on to the next driver. There is nothing in the CSD that gives additional information as to whether or not a compensation network can mitigate. Nothing.
Again, the CSD is useless. All it is good for is showing the neophyte that, yes, indeed, the raw driver has a set of various resonances of some magnitude and Q. Period. It does nothing else. Emphasis on the CSD is misdirected.
No, it's the absolute truth because whether experienced or not, the CSD provides NO additional USEFUL information that one needs to design. Nothing. Any and all non-linearities that are the result of the resonances are in the FR and include step and diffraction for that measurement position. One need ONLY the FR, coupled with distortion data if available and the impedance to determine and design.
Please direct us to this quote. I'm not aware of anyone making such a blanket statement. This is a specious argument put this way and I believe untrue. Use the direct quote for clarity if there is such. I don't think that you'll find it.
This is so clearly evident in the FR that it would be wasted time inspecting the CSD. Yes, again, useless to look at the CSD.
If this is the same setup as the others it's useless to try to determine the driver's response below 1KHz, or anywhere for that matter, with contaminated data. You've got the same 2.88ms start and a 7.85ms stop. I'm sorry, this is just lame.
All of which is evidence that if the user cannot properly set up a measurement to exclude reflections, it's the error of the person making the measurement. Contaminated data proves nothing. It's a simple task in such a case to find the proper point for the marker. One would assume that the measurement conditions are under control. This is a strawman argument if ever there was one. This is the same baseless kind of argument that you used in the beginning, using purposely contaminated data. It simply undermines your position.
The errors can be and often are much larger. They could easily swing +/- 5db, but in any case it's a limit of the window used. You can't seriously be arguing that a 3ms window of an impulse is valid? Ridges can appear or disappear depending on the users ability and even with small changes in the window length. In any case, there is not enough data below that point to be considered accurate given the short time samples of the examples.
We've all commented, only it's been to point out the serious shortcoming of your argument.
Here is a direct quote from your first post taking us to task:
This is an absolute statement, no equivocation. Do you stand by this? Let's have no equivocating now, yes or no, do you stand by this statement that you said previously or not?
Another quote from that first post:
[QUOTE
The more I view the CSD...
the closer I am to dismissing them out of hand due to not only the limitations of most impulse responses used that only allow for too-short a window due to reflections, but also for the misunderstandings as to what it shows with regard to what mitigation is possible.
I had questioned SL over at Madisound on them at one time as he didn't like them for the limits of graphical display, but this was a limitation of MLSSA at the time (and Clio apparently) and possibly may still be so. He was unresponsive when I pointed out that LAUD has the scale and time axes fully at the users control. At this point, I do not view the CSD for any design purpose at all. It's not needed.
Dave
the closer I am to dismissing them out of hand due to not only the limitations of most impulse responses used that only allow for too-short a window due to reflections, but also for the misunderstandings as to what it shows with regard to what mitigation is possible.
I had questioned SL over at Madisound on them at one time as he didn't like them for the limits of graphical display, but this was a limitation of MLSSA at the time (and Clio apparently) and possibly may still be so. He was unresponsive when I pointed out that LAUD has the scale and time axes fully at the users control. At this point, I do not view the CSD for any design purpose at all. It's not needed.
Dave
Dave, your long winded ramble wasn't worth the time it took to read it much less respond to any of it.
Same old same old, blah, blah, blah... Say whatever you like...
Bottom line is that you had plenty of opportunity to demonstrate this but did not. You were too afraid to comment on the posted measurements even when the two drivers were completely different to the largest degree.
The only thing you have demonstrated the propensity of your own opinion.
Same old same old, blah, blah, blah... Say whatever you like...
Bottom line is that you had plenty of opportunity to demonstrate this but did not. You were too afraid to comment on the posted measurements even when the two drivers were completely different to the largest degree.
The only thing you have demonstrated the propensity of your own opinion.
Ah yes, the classic dodge
"Wasn't worth reading...". Whenever you can't or won't respond, this is your classic response. It's evident that you can't because you know that you can't back up your previous unequivocal statements. We've seen it before.
I can and still will provide evidence as I said I would. It should make for an interesting page at my site. There will be no question as to the facts.
Dave
Danny said:
"Wasn't worth reading...". Whenever you can't or won't respond, this is your classic response. It's evident that you can't because you know that you can't back up your previous unequivocal statements. We've seen it before.
I can and still will provide evidence as I said I would. It should make for an interesting page at my site. There will be no question as to the facts.
Dave
I did
I did. I also quoted some of Danny's own words. He cannot support those unequivocal statements of his. Also consider his lame attempts at "gotcha's", then trying to make good afterward. His graphs and data are simply not trustworthy given his history in the posts. It's by design a lost cause.
I never use nor do I have any use for the CSD to design, none whatsoever and that has been my point from the beginning. Anyone who knows their stuff also knows this. The FR has what is needed outside of actual distortion measurements. CAD software operates strictly on the FR for all but the most advanced versions that have additional capability, but the basics are the same. The CSD has no place nor any requirement in actual design. I dare say that you will never find any software that uses it for anything other than a flashy graph.
It is also subject to misinterpretation and is also inaccurate and incomplete when short windows are used for the FFT, such as the examples here. The resolution on the frequency axis is the primary problem. The magnitude also suffers at the low end, but it's primarily the extremely limited frequency resolution that makes them suspect, mostly below about 1KHz. That's a fact of the MLS and the FFT from which the CSD is determined. Protests to the contrary and whimsical and indeterminant measures of "most stored energy" are not based in fact. Danny wants everything on his terms, but won't even define them when pressed, as I did more than once.
Dave
pinkmouse said:
Guys, stick to facts, don't bring personalities into the argument.
I did. I also quoted some of Danny's own words. He cannot support those unequivocal statements of his. Also consider his lame attempts at "gotcha's", then trying to make good afterward. His graphs and data are simply not trustworthy given his history in the posts. It's by design a lost cause.
I never use nor do I have any use for the CSD to design, none whatsoever and that has been my point from the beginning. Anyone who knows their stuff also knows this. The FR has what is needed outside of actual distortion measurements. CAD software operates strictly on the FR for all but the most advanced versions that have additional capability, but the basics are the same. The CSD has no place nor any requirement in actual design. I dare say that you will never find any software that uses it for anything other than a flashy graph.
It is also subject to misinterpretation and is also inaccurate and incomplete when short windows are used for the FFT, such as the examples here. The resolution on the frequency axis is the primary problem. The magnitude also suffers at the low end, but it's primarily the extremely limited frequency resolution that makes them suspect, mostly below about 1KHz. That's a fact of the MLS and the FFT from which the CSD is determined. Protests to the contrary and whimsical and indeterminant measures of "most stored energy" are not based in fact. Danny wants everything on his terms, but won't even define them when pressed, as I did more than once.
Dave
My point, and Nice Work Zaph
I want to clarify something here, some asked if FR tests were influenced by non-linear aspects of the driver or system under test and I provided the above extreme example to show that indeed they are. People seem to be jumping to the conclusion that this was the previous point I was trying to make which is not the case. My previous point was that even if you EQ all 7 peaks in the L18 frequency response, you need to then consider differences in the distortion performance when comparing two drivers and that the linear EQ could not possibly make the distortion of the two drivers the same.
I want to make it clear that this was my point all along.
I also want to mention that I respect Zaph's work, and the P18 was not available when he did that design so it is easy to see why he might have chosen it. Today, I'd choose the P18 for this low cost application. The much more expensive SEAS EXcel metal cone drivers provide much better distortion and FR than the L18 and I would consider these also in a higher cost system. Still, speaker design and psychoacoustic considerations are complex and I can see why Zaph might have been curious to try the L18 to determine their performance in a real world application.
Pete B.
PB2 said:
I want to clarify something here, some asked if FR tests were influenced by non-linear aspects of the driver or system under test and I provided the above extreme example to show that indeed they are. People seem to be jumping to the conclusion that this was the previous point I was trying to make which is not the case. My previous point was that even if you EQ all 7 peaks in the L18 frequency response, you need to then consider differences in the distortion performance when comparing two drivers and that the linear EQ could not possibly make the distortion of the two drivers the same.
I want to make it clear that this was my point all along.
I also want to mention that I respect Zaph's work, and the P18 was not available when he did that design so it is easy to see why he might have chosen it. Today, I'd choose the P18 for this low cost application. The much more expensive SEAS EXcel metal cone drivers provide much better distortion and FR than the L18 and I would consider these also in a higher cost system. Still, speaker design and psychoacoustic considerations are complex and I can see why Zaph might have been curious to try the L18 to determine their performance in a real world application.
Pete B.
If the statement that all of the CSD's data is present in the FR (which is quite obviously missing one of the vectors in the linear system [Frequency][Amplitude][Time], namely... [Time] ! - a vector of no small importance), then the following would be true:
This is of course concerning ONE driver - in an almost perfect infinite baffle with no non-linear external influences like reflections or external non-linear hard resonances - someone earlier in this thread stated that all drivers in themselves are Minimum Phase, (mostly) Linear Systems... So lets see
1. A well thought out and implemented Impulse Measurement is made, or the Impulse is synthesized with one of the many available models (MLS, swept sine with inverse convolution or any of the others)
2. A well balanced CSD is plotted from the Impulse in (1.). And it is saved for later purposes. No conclusions will be drawn from this plot now.
3. The mathemathical conversion from f(Amplitude)of(Time) - the Impulse - to f(Amplitude)of(Frequency) - the FR plot - is made (with FFT, windowed or 0-padded). This is then a [Time]-independant plot. Obviously.
4. The mathematical conversion from f(Amplitude)of(Frequency) to f(Amplitude)of(Time) is made (step no. 3. is reversed). This is what some people here claim they can do - in their heads.
5. The Impulse generated by step 4 is used to make another CSD with exactly the same window(s) and resolution as the one made from the original impulse in step 2.
6. Compare the two impulses - the original and the one with [Time] removed from the linear system (the one in step 4. This what we actually have done by converting from the original impulse to a static FR)
They should be the same if the argument that CSD is entirely FR dependant is true.
7. Compare the two CSD's. They should be the same if the argument that CSD is entirely FR dependant is true.
....................
And now we return to reality.
This is what WILL happen:
Steps (6.) and (7.) will show significant differences between the two versions.
These differences will be larger or smaller *(or lets just say - different) depending on the non-linearities and the energy-storage properties of the chosen driver.
These differences will NOT scale in a linear fashion if the amplitude of the impulse is changed (more or less power fed to the driver in step (1.)). The differences will NOT be the same. More non-linearities.
This said - I have to agree that MOST OF THE TIME, most of the energy-storage in a driver CAN be roughly estimated by looking at the FR. But this will be an educated guess, not a truth. Most of the time, this will be enough, but....
IT WILL STILL NOT BE TRUE AND SHOULD NOT BE STATED AS FACT!
This has been done and documented. By more proficient organizations and persons than me. I will not make my own measurements regarding this experiment all over again just to satisfy someone that disagrees with this statement.
I will follow a well functioning and universaly accepted scientific procedure - my statement is true unless someone PROVES it to be untrue.
So - please.....
Make my statement fail by following my 7 steps and publish your results here
This will not happen.
(But btw - I usually only use FR's when designing loudspeaker systems... I cannot afford the luxury of allways buying lots of different drivers to compare their non-linear resonant behaviours. But I would like to... And I HAVE done exactly that a few times - for systems that I myself will use AND there are in my personal opinion audible differences between drivers that i chose from, even when equalized (with X-over) to the same FR! Even if the THD's are very similar. This was a by-comment)
I do hope that haven't made any personal enemies by writing this. That was not my intent.
Greetings from sweden... /Joakim
This is of course concerning ONE driver - in an almost perfect infinite baffle with no non-linear external influences like reflections or external non-linear hard resonances - someone earlier in this thread stated that all drivers in themselves are Minimum Phase, (mostly) Linear Systems... So lets see
1. A well thought out and implemented Impulse Measurement is made, or the Impulse is synthesized with one of the many available models (MLS, swept sine with inverse convolution or any of the others)
2. A well balanced CSD is plotted from the Impulse in (1.). And it is saved for later purposes. No conclusions will be drawn from this plot now.
3. The mathemathical conversion from f(Amplitude)of(Time) - the Impulse - to f(Amplitude)of(Frequency) - the FR plot - is made (with FFT, windowed or 0-padded). This is then a [Time]-independant plot. Obviously.
4. The mathematical conversion from f(Amplitude)of(Frequency) to f(Amplitude)of(Time) is made (step no. 3. is reversed). This is what some people here claim they can do - in their heads.
5. The Impulse generated by step 4 is used to make another CSD with exactly the same window(s) and resolution as the one made from the original impulse in step 2.
6. Compare the two impulses - the original and the one with [Time] removed from the linear system (the one in step 4. This what we actually have done by converting from the original impulse to a static FR)
They should be the same if the argument that CSD is entirely FR dependant is true.
7. Compare the two CSD's. They should be the same if the argument that CSD is entirely FR dependant is true.
....................
And now we return to reality.
This is what WILL happen:
Steps (6.) and (7.) will show significant differences between the two versions.
These differences will be larger or smaller *(or lets just say - different) depending on the non-linearities and the energy-storage properties of the chosen driver.
These differences will NOT scale in a linear fashion if the amplitude of the impulse is changed (more or less power fed to the driver in step (1.)). The differences will NOT be the same. More non-linearities.
This said - I have to agree that MOST OF THE TIME, most of the energy-storage in a driver CAN be roughly estimated by looking at the FR. But this will be an educated guess, not a truth. Most of the time, this will be enough, but....
IT WILL STILL NOT BE TRUE AND SHOULD NOT BE STATED AS FACT!
This has been done and documented. By more proficient organizations and persons than me. I will not make my own measurements regarding this experiment all over again just to satisfy someone that disagrees with this statement.
I will follow a well functioning and universaly accepted scientific procedure - my statement is true unless someone PROVES it to be untrue.
So - please.....
Make my statement fail by following my 7 steps and publish your results here
This will not happen.
(But btw - I usually only use FR's when designing loudspeaker systems...
I cannot afford the luxury of allways buying lots of different drivers to compare their non-linear resonant behaviours. But I would like to... And I HAVE done exactly that a few times - for systems that I myself will use AND there are in my personal opinion audible differences between drivers that i chose from, even when equalized (with X-over) to the same FR! Even if the THD's are very similar. This was a by-comment)I do hope that haven't made any personal enemies by writing this. That was not my intent.
Greetings from sweden...
/Joakim
I've been making my way through this thread for last few days and I have to say I've learnt a thing or two.
Without getting drawn into the debate and instead just giving some acknowledgement for an interesting thread. I think John sums up much of what has been said in this thread with illustrative graphs and concise, easy to understand text. This can be found on his blog page here:
http://www.zaphaudio.com/blog.html
Hopefully he leaves that info up for awhile so others can take a look.
With regard to CSD proponents, I see where they're coming from. I thought the same way up until I read this thread but John, Mark and David make a lot of sense once I'd bashed that info into my head hard enough.
Cheers for the discussion guys. I'm a little wiser.
Without getting drawn into the debate and instead just giving some acknowledgement for an interesting thread. I think John sums up much of what has been said in this thread with illustrative graphs and concise, easy to understand text. This can be found on his blog page here:
http://www.zaphaudio.com/blog.html
Hopefully he leaves that info up for awhile so others can take a look.
With regard to CSD proponents, I see where they're coming from. I thought the same way up until I read this thread but John, Mark and David make a lot of sense once I'd bashed that info into my head hard enough.
Cheers for the discussion guys. I'm a little wiser.
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