# Audiofrog GB60 and Stereo Integrity TM65 mkII



## Justin Zazzi (May 28, 2012)

I sincerely apologize for the delay between when some of you so graciously loaned me the drivers for this project and when I am finally posting the results now. It is painful to share why that is, and I hope we can not dwell on it since I have no interest in discussing it. Thank you for your encouragement to finish this project, and I am really excited to be able to share this with you all now.

The report is on my dropbox and linked below. Feel free to enjoy and share it. I will be leaving the country for vacation in about a week so I will answer questions as best I can until then.

I must thank both Andy Wehmeyer and Nick Lemons from Stereo Integrity for being open to discussing this project and helping to make it better than I could have done alone. Also thank you to the folks who helped proofread it.

And so, here it is.

---> GB60 vs TM65ii version 2.11 <---


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## Weightless (May 5, 2005)

7 hours and not a single comment, lol.

Thanks Justin for the work you've put into this. I will be reading this while sitting in the waiting room of my dentist...



Sent from my SM-N920P using Tapatalk


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## I800C0LLECT (Jan 26, 2009)

Just read through it. I had no idea it was posted! Don't need any apologies either!... Stellar performance

It looks like everybody's observations are in line with what Jazzi reported. Glad to see you were able to push through personal and forum struggles. Hopefully it didn't place too big of a chip on your shoulder. We can't please everyone around here.

We just needed to be more mature with our expectations and do our best to understand how the data relates to real world. They're both great mid-bass speakers. Great job on the write up


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## EricP72 (Mar 23, 2008)

I haven't read it yet, but just wanted to say thanks in advance!


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## seafish (Aug 1, 2012)

What a useful, well written and professional examination and write-up of these speakers... GREAT job and MANY thanks!!!!


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## kmbkk (Jun 11, 2011)

Dang it, I can't view it at work. Oh well, I guess I'll look at it tonight. Anyway, thank you for doing this, and like others have said, no apologies needed.


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## I800C0LLECT (Jan 26, 2009)

kmbkk said:


> Dang it, I can't view it at work. Oh well, I guess I'll look at it tonight. Anyway, thank you for doing this, and like others have said, no apologies needed.


When I downloaded the files using the browsers "direct download" option they were corrupted. I installed drop box on my phone and the file worked properly.

Hope that helps


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## Truthunter (Jun 15, 2015)

Very well written, easy to understand, and educational. Thanks :thumbsup:


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## benny z (Mar 17, 2008)

Well done. Very thorough and fun to read. Props to you!


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## gwalsh (Sep 15, 2013)

Excellent and thorough read - thank you!!!


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## mrichard89 (Sep 29, 2016)

Great write up! Thanks for your time and efforts.


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## SkizeR (Apr 19, 2011)

Justin, this is great. Thank you!


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## 555nova (Apr 12, 2014)

Thank you for the time and effort you put into this.


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## EmptyKim (Jun 17, 2010)

Awesome write up.


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## dcfis (Sep 9, 2016)

Just read it. What a fantastic first published paper! I wish my first dozen were as good. You got a knack for this kid!


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## SkizeR (Apr 19, 2011)

dcfis said:


> You got a knack for this kid!


hmmm.. so what drivers are we sending him next? lol


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## Golden Ear (Oct 14, 2012)

Love the objective testing and write-up. Thanks for taking the time for the benefit of everyone! 


Sent from my iPhone using Tapatalk


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## Elgrosso (Jun 15, 2013)

Wow this is great thank you Jazzi, very well explained even more than Vance, and worth the wait. The thermal compression plots are really cool.


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## gijoe (Mar 25, 2008)

Thanks for this! It looks to me that if cost wasn't an issue (which in the real world it obviously is) that the Audio Frog is simply a better driver. It plays higher, handles heat better, and does just as well as a midbass (it's only down by a dB or two, but not much). It's a shame that the suspension on the TM65 prevents the motor from shinning.


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## Viggen (May 2, 2011)

Thanks for doing this and looking forward to reading your article

Most forums kinda become ghost towns around Xmas-new years....


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## ErinH (Feb 14, 2007)

First of all, thank you, Justin, for taking the time to do this and publish the results in such a well-documented format. It’s very much appreciated. 

I have some comments regarding your testing/paper (now you can roll your eyes…). Some geared more as questions/concerns to you and some that people reading your report need to also consider when they review the results. You may brush these off… I hope you don’t. I am in no way trying to demean your efforts or appear like I’m a know-it-all. So, please keep that in mind when reading my comments below. Take this as words from someone with some experience not only testing but analyzing mountains of data. 

*Small Signal Parameters:*

Do you have Impedance Plots? Those can often go a long way to differentiating ‘environment’ vs ‘driver’ borne anomalies. And can also explain distortion issues (see comments below regarding request for HD/IMD vs frequency data).

*Measured frequency response vs published:*

That mic stand itself will create comb filtering in the frequency response measurements. Yes, I’m serious: Loudspeaker Measurements
You noted the SI’s published FR was measured in the nearfield, however you still overlaid your on-axis farfield data. It would have been more accurate to overlay your nearfield data and then provide your farfield/nearfield measurement separately. 
When you measured off-axis, which way did you move the mic? Toward the baffle side or toward the free-space side? I’m guessing the baffle side but I dunno. The results would obviously differ (which you would immediately realize when you compare the impulse measurements between the two) and knowing might help me better understand what’s going on in the higher frequency areas. 
The impulse duration being 2.5ms is pretty short. When you break that down, that’s a data point only about every 400hz. I’d really like to see the nearfield and farfield measurements here. Looking at the FR, I see you ‘stitched’ together your nearfield and farfield results at about 350hz. If you look at the FR of both drivers you'll see a 'trough' of sorts in the midrange. Given your window is only really good down to 400hz (again, the 2.5ms impulse window), I think the ~350hz stitching point may have been too low and that’s driving the 'trough' to appear the way it does. Your farfield lower limit should not be lower than the equivalent of your window time; otherwise you get bad data. I typically stitch at least an octave above my time window. Not only to avoid any comb filtering from reflections but also to mitigate the baffle’s effect which I mentioned when you started your testing. The purpose of the nearfield is to attempt to ignore the baffle in the lower frequencies but by setting your splice at 350hz you’re letting all that in. I gave an example of the differences here: 













*Xmax Considerations:*

You mentioned 70% Bl. That would be used when determining a 20% THD limit. Twenty-percent THD is typically only used for subwoofer testing due to decreased perception of distortion with lowered frequency. For everything else 10% THD is used, which would equate to 82% Bl. For more info see this:


Voice Coil Magazine said:


> The 12CXA400Nd’s displacement limiting numbers, which were calculated by the Klippel analyzer, were XBl at 82% (Bl decreasing to 82% of its maximum value) was 3.6 mm. For crossover (XC) at 75% (compliance decreasing to 75% of its maximum value), it was 4.8 mm. For the 12CXA400Nd, the Bl is the most limiting factor at the prescribed distortion level of 10%. However, 10% may be somewhat conservative given the relative difficulty of subjectively perceiving total harmonic distortion (THD). If we apply the 20% distortion criteria with Bl decreasing to 70% and compliance decreasing to 50%, then the numbers are XBl = 4. 8mm and XC = >7.85 mm.



Note, also, that the xmax on the “acoustic distortion” method you used to determine the xmax is based on 10% THD (page 2 of Application Note 4, “Practical Usage” section, item 5) so when you talk about using xmax values based on “acoustic distortion” and compare that to the Bl-derived distortion xmax, you are comparing xmax values at two different THD levels (10% via acoustic measurement, 20% via Bl). Unless there’s a way to change the value which the AN didn’t address. 
Do you have inductance over excursion data? For drivers used near Fs this is as important - if not more important than - Bl and Cms/Kms. Why? Because as Geddes’ work has shown there’s a weighted threshold for distortion audibility. (This also explains why a more relaxed 20% THD value is used for subwoofers when determining xmax.) When using a driver in both a low and high frequency application (typical for mid/woofer like the ones you’ve tested) it is playing at/near Fs as well as many octaves above. This can lead to a type of distortion known as Intermodulated Distortion (IMD). Reading the Klippel Application Note (AN) 04 you referenced, I see they are using two stimuli: one at Fs and the other at 8.5*Fs. That means the test is of an IMD type. Good. But seeing the inductance curves would be useful to understanding what the primary factor for distortion is. Not just ‘because’, but rather so we can possibly glean a more proper ‘best usage’ case for these drivers. Since you provided both Bl(x) and Kms(x) then you should already have Le(x) and Le(i). 
Speaking of Application Note 4, where is the data from that? You summarized the results but where is the data to supplement your analysis? I’d be interested in seeing how the distortion components change as voltage is increased. That would also be useful to determining how influential something like the offset suspension curve of the SI is, as you would expect it to show up in 2nd order distortion plots.
Do you have the LSI results for xmax? I’m looking for the section of results that breaks down the xmax limits for each of the main contributing factors (Bl(x), Cms(x), Le(x), Le(i))?


Finally, did you perform any HD or IMD tests where you swept signal (HD testing) or ‘swept’ a signal while keeping a constant f1 (IMD testing)? I’m asking because it would be useful to see how the distortion profile changes with frequency rather than just seeing distortion at Fs since that defines only the lower bound. There can be other distortion issues higher in frequency (i.e.; cone/surround discontinuity that yields high 2nd order distortions in the 800-2khz region, breakup distortions that may show users more reasons why crossing above the beaming point will result in bad sound). HD results are an excellent complement to FR polars.




You may choose to brush these comments off and that’s your prerogative. I want to reiterate I’m only trying to help you improve your work and provide the community some education at the same time. It doesn’t mean I don’t appreciate the work you did and time you spent. 

-	Erin


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## ErinH (Feb 14, 2007)

Now, moving on to the data you provided…


*Frequency Response:*

The off-axis measurements are great! Much appreciated! What I see in this regard is two drivers with really solid polar response. I also liked your evaluations. 
While the polars look good, meaning how each off-axis measurement compares to on-axis measurement, the FR as a singular is kind of wonky. Both drivers exhibit a ‘trough’ in the upper midrange. I wonder how much of this is baffle based, in conjunction with their respective Qts values. Or if this is due to the frequency you chose to stitch the data together which I expressed concern over in my previous post. You covered the upper frequency response concerns very well. Nothing for me to add here.

*Xmax Stuff:*

The xmax values are interesting. Again, it would be nice to have inductance curves with it. From only Bl and Kms it looks like the xmax values, using 10% THD method, are:
[*]GB60 Bl = 5.8mm, Kms = 5.8mm
[*]SI Bl = 7.5mm, Kms = 2.8mm (due to the asymmetry of the curve*)
[*]*I can’t tell if the SI Kms is offset by nearly 6mm of if it really is just bad asymmetry; LSI provides an output called “Symmetry Range” that would answer this.​
Using the 20% THD method, I get:
[*]GB60 Bl = 6.8mm, Kms = 8.5mm
[*]SI Bl = 9mm, Kms = 7mm​
Using a high-pass filter will remedy the suspension issues with the SI. But, I think maybe these results lend credence to the bit I mentioned earlier regarding distortion audibility lower in the frequency spectrum. The data suggests a lot of ‘room for error’ between 10 and 20% THD (as evidenced by the 2.8mm at 10% vs the 7mm at 20% in Kms-related xmax limitations). I heard these in Nick’s car last Summer and while we didn’t put the drivers in to submission, we definitely beat on the system. He was using a 20hz/24dB filter simply to protect the drivers which was nearly 2 octaves below the Fs. I didn't hear anything that stood out during my demo. That doesn't mean it wasn't there. Just that it wasn't there, or certainly not obvious during my demo. I've heard others say the same thing. May be anecdotal but interesting, nonetheless. 



Overall, as someone already said, I don’t think we have many surprises here. What we do have is some good data to help people understand the reasoning for making choices. Good stuff all around. Thanks again, Justin.


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## Holmz (Jul 12, 2017)

ErinH said:


> First of all, thank you, Justin, for taking the time to do this and publish the results in such a well-documented format. It’s very much appreciated.
> ...
> Finally, did you perform any HD or IMD tests where you swept signal (HD testing) or ‘swept’ a signal while keeping a constant f1 (IMD testing)? I’m asking because it would be useful to see how the distortion profile changes with frequency rather than just seeing distortion at Fs since that defines only the lower bound. There can be other distortion issues higher in frequency (i.e.; cone/surround discontinuity that yields high 2nd order distortions in the 800-2khz region, breakup distortions that may show users more reasons why crossing above the beaming point will result in bad sound). HD results are an excellent complement to FR polars.
> ...


It was very kind of you to provide critique of Justin's work.
(Which, to my armature eyes, was already pretty good)

I am sure there are many important numbers, but when choosing a midbass I looked at the HD/IMD curves, which almost no manufacturer provides.

The ones I selected had the lowest distortion, and were also touted as some of the best tested.

If there are two things to see, for me it is sensitivity and distortion plots.


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## Rocky98Formula (Jul 13, 2017)

I don't own either of these speakers but enjoyed reading the report. Learned a lot from it and knowing is half the battle!

Thank you for taking the time to do this.


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## finfinder (Apr 15, 2006)

Well done .. it took stones to even attempt something like this.. much less do it well.


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## rton20s (Feb 14, 2011)

Thank you Justin for all of the work you put into this and providing the such a well put together report. Also a big thank you to all of those that provided drivers. I look forward to seeing what you do as you move into making speaker design your profession. 

And since Erin has opened the gate, I have my own critique of your published results...

In the "Conclusions" section, under the TM65 MkII, "+more affordable" is listed twice. 

For some of us, that particular aspect might be twice as important than all of the others in the pro/con list. So, maybe that was intentional.


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## Babs (Jul 6, 2007)

Good stuff! As stated, this took some major brass ones to dive into. Justin this took big work! 

On speaker measurement and the good history of it on DIYMA, Justin and Erin both, thank you guys for this new work, and Erin for your work years past on many different drivers. They are still a go-to for me for reference on certain drivers. 

A good and thorough attempt at this level to really analyze the performance of speaker drivers I always find impressive. Justin I believe you are on a great path of discovery in the hobby. I imagine not only did you learn a lot about these drivers, but in the process as well. Kudo's o' plenty!


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## unix_usr (Dec 4, 2013)

Awesome work man - great read. Super curious how the si tm65 (mk one) would have fit in this list... The GB60 is on my list, but also on the list of "wifey will kill me if i spend that much more"... interesting perspective on performance though. 


Sent from my iPhone using Tapatalk


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## Justin Zazzi (May 28, 2012)

ErinH said:


> First of all, thank you, Justin, for taking the time to do this and publish the results in such a well-documented format. It’s very much appreciated.
> 
> I have some comments regarding your testing/paper (now you can roll your eyes…). Some geared more as questions/concerns to you and some that people reading your report need to also consider when they review the results. You may brush these off… I hope you don’t. I have am in no way trying to demean your efforts or appear like I’m a know-it-all. So, please keep that in mind when reading my comments below. Take this as words from someone with some experience not only testing but analyzing mountains of data.


Thank you for the kind words and I appreciate the thought that you put into your reply. I will do my best to respond to your questions.


ErinH said:


> *Small Signal Parameters:*
> Do you have Impedance Plots? Those can often go a long way to differentiating ‘environment’ vs ‘driver’ borne anomalies. And can also explain distortion issues (see comments below regarding request for HD/IMD vs frequency data).


Yes I do, and I didn't think to post them but I will.


ErinH said:


> You state the SI has “dramatically lower measured sensitivity than published (about -3 db lower!)”… Then you state sensitivity alone does not tell the whole story. The expletive (!), however, implies otherwise.


The exclamation mark is referring to the mismatch between the published and the measured valued. You are right that I also mention this single number is not as important as it sounds though.


ErinH said:


> *Measured frequency response vs published:*
> That mic stand itself will create comb filtering in the frequency response measurements. Yes, I’m serious...


You're right the mic stand can contribute to some comb filtering. I minimized the by using a mic stand that holds the microphone "far" away from the base in a similar dimension to the nearest edge of the wood baffle I built. Then when using the 3.0ms window, the reflections from both the baffle and the mic stand/base are removed. There still might be some reflections off the mic clip itself, and that is more difficult to control. I tried to address this when I mention that the high frequencies are less reliable since any small surface can cause reflections and influence the data.


ErinH said:


> You noted the SI’s published FR was measured in the nearfield, however you still overlaid your on-axis farfield data. It would have been more accurate to overlay your nearfield data and then provide your farfield/nearfield measurement separately.


This is incorrect. The trace I overlaid on top of the TM65ii's frequency response was made in the near field and smoothed to 24dB/octave. I did this on purpose to try and match the conditions that the manufacturer stated was used to make their frequency response. You can see the black trace in that graphic (near field) is different from any of the traces in the polar measurements I made (in the far field). I tried to mention this in the paragraph near that graphic but my wording was not very clear. I will try to make that more clear.


ErinH said:


> When you measured off-axis, which way did you move the mic? Toward the baffle side or toward the free-space side? I’m guessing the baffle side but I dunno. The results would obviously differ (which you would immediately realize when you compare the impulse measurements between the two) and knowing might help me better understand what’s going on in the higher frequency areas.


I moved the microphone toward the baffle side, which is exactly why I designed the baffle to be extended longer on one side and the entire baffle shape is not just a square shape. You keenly noticed that if I were to use a square baffle to make polar measurements, then the time of the first reflection arrival (edge diffraction) would change and I would have to use different FFT time windows for each off-axis measurement. You can see I laid scrap wood on the ground in 15 degree increments so that my microphone alignments were more consistent. 


ErinH said:


> The impulse duration being 2.5ms is pretty short. When you break that down, that’s a data point only about every 400hz. I’d really like to see the nearfield and farfield measurements here. Looking at the FR, I see you ‘stitched’ together your nearfield and farfield results at about 350hz. If you look at the FR of both drivers you'll see a 'trough' of sorts in the midrange. Given your window is only really good down to 400hz (again, the 2.5ms impulse window), I think the ~350hz stitching point may have been too low and that’s driving the 'trough' to appear the way it does. Your farfield lower limit should not be lower than the equivalent of your window time; otherwise you get bad data. I typically stitch at least an octave above my time window. Not only to avoid any comb filtering from reflections but also to mitigate the baffle’s effect which I mentioned when you started your testing. The purpose of the nearfield is to attempt to ignore the baffle in the lower frequencies but by setting your splice at 350hz you’re letting all that in. I gave an example of the differences here...


Very good catch. I mistakenly reported a window length of 2.5ms but the window is actually 3.0ms which corresponds to a frequency resolution of 333hz and this is where I stitched the nearfield and farfield responses together. As for the trough in both sets of far field measurements, I will look into that. It could always be an anomaly in my setup and if it is I would like to find the flaw in my method. Below are the nearfield traces (for all frequencies) overlaid on the far-field traces (still 3.0ms windowed and stopping at 333hz). What do you see below?






















ErinH said:


> *Xmax Considerations:*
> You mentioned 70% Bl. That would be used when determining a 20% THD limit. Twenty-percent THD is typically only used for subwoofer testing due to decreased perception of distortion with lowered frequency. For everything else 10% THD is used, which would equate to 82% Bl. For more info see this...


I was using 70% of BL since this is what was used by Stereo Integrity when quoting the Xmax value that is published in their literature and on their website (searching for a 30% decay in BL strength when running a finite element analysis with a program such as FEMM). My intention was to show that the published value for Xmax is not unreasonable given the tools that the manufacturer used to determine it, however there are more precise methods to get a better value. Unfortunately, the better tools (like the Klippel distortion analyzer) are tens of thousands of dollars. 


ErinH said:


> Note, also, that the xmax on the “acoustic distortion” method you used to determine the xmax is based on 10% THD (page 2 of Application Note 4, “Practical Usage” section, item 5) so when you talk about using xmax values based on “acoustic distortion” and compare that to the Bl-derived distortion xmax, you are comparing xmax values at two different THD levels (10% via acoustic measurement, 20% via Bl). Unless there’s a way to change the value which the AN didn’t address.


Exactly. Many methods can be used to measure Xmax since it is poorly defined. I tried to make it clear which method the manufacturers used, which method I used, and why there was a difference. It is not difficult to change the procedure in application note 4 to find 20% THD, however it would require running the test with different protection limits that would have a higher chance of damaging the woofer since it would have to be stressed harder. The key point I was trying to make in all of this is that the BL curve alone doesn't tell the whole story since the suspension can contribute just as much, if not more, acoustic distortion to our ears.


ErinH said:


> Do you have inductance over excursion data? For drivers used near Fs this is as important - if not more important than - Bl and Cms/Kms. Why? Because as Geddes’ work has shown there’s a weighted threshold for distortion audibility. (This also explains why a more relaxed 20% THD value is used for subwoofers when determining xmax.) When using a driver in both a low and high frequency application (typical for mid/woofer like the ones you’ve tested) it is playing at/near Fs as well as many octaves above. This can lead to a type of distortion known as Intermodulated Distortion (IMD). Reading the Klippel Application Note (AN) 04 you referenced, I see they are using two stimuli: one at Fs and the other at 8.5*Fs. That means the test is of an IMD type. Good. But seeing the inductance curves would be useful to understanding what the primary factor for distortion is. Not just ‘because’, but rather so we can possibly glean a more proper ‘best usage’ case for these drivers. Since you provided both Bl(x) and Kms(x) then you should already have Le(x) and Le(i).


I do have all of this information too, however the depth of detail has to stop somewhere right? I felt this much information would be less valuable to this audience and I didn't feel comfortable enough explaining it in a way that wouldn't make it feel more complicated. If you're interested in pursuing this further lets chat somewhere on the side until I have a better understanding and can present it more clearly.

I am curious about the work you refer to from Geddes. Where can I find this?


ErinH said:


> Speaking of Application Note 4, where is the data from that? You summarized the results but where is the data to supplement your analysis? I’d be interested in seeing how the distortion components change as voltage is increased. That would also be useful to determining how influential something like the offset suspension curve of the SI is, as you would expect it to show up in 2nd order distortion plots.


The distortion components are based on voltage (or excursion) but also frequency. The way the Klippel dB-Lab software is laid out makes this impossible to see in a single chart and requires correlating data from one graph to another while simultaneously changing display settings which is not easy to display or explain. If you know of an easy way to display to view this, I would love to hear about it.


ErinH said:


> Do you have the LSI results for xmax? I’m looking for the section of results that breaks down the xmax limits for each of the main contributing factors (Bl(x), Cms(x), Le(x), Le(i))?


I believe I have what you are looking for. This requires setting the limits of acceptable deviation for each of these parameters though (like 82% for BL, etc). However we would have to agree on what limits to use for BL, Kms, and Le(x). I do not see a section in that window showing excursion limits based on Le(I), but the other windows show Le(I) contributes nearly zero distortion to either woofer.

I think in general you're interested in which distortion is the primary contributing factor? For the GB60 the suspension and motor are 50/50, and the inductance is negligible. For the TM65ii the suspension is heavily dominant and the motor and inductance are well behaved out to roughly 6mm where they increase.



ErinH said:


> Finally, did you perform any HD or IMD tests where you swept signal (HD testing) or ‘swept’ a signal while keeping a constant f1 (IMD testing)? I’m asking because it would be useful to see how the distortion profile changes with frequency rather than just seeing distortion at Fs since that defines only the lower bound. There can be other distortion issues higher in frequency (i.e.; cone/surround discontinuity that yields high 2nd order distortions in the 800-2khz region, breakup distortions that may show users more reasons why crossing above the beaming point will result in bad sound). HD results are an excellent complement to FR polars.


The distortion plots from the Klippel X10 module only go up to 320 hz since that is the limit I set in consideration of the time required to keep going. I don't believe I have what you're looking for here.


ErinH said:


> You may choose to brush these comments off and that’s your prerogative. I want to reiterate I’m only trying to help you improve your work and provide the community some education at the same time. It doesn’t mean I don’t appreciate the work you did and time you spent.
> -	Erin


Understood and greatly appreciated!


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## Justin Zazzi (May 28, 2012)

ErinH said:


> ........
> *I can’t tell if the SI Kms is offset by nearly 6mm of if it really is just bad asymmetry; LSI provides an output called “Symmetry Range” that would answer this.


Yep, the suspension on the TM65ii as very asymmetrical. I went full retard and destroyed a driver in the process to learn more about that specifically


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## Justin Zazzi (May 28, 2012)

rton20s said:


> ........
> In the "Conclusions" section, under the TM65 MkII, "+more affordable" is listed twice.
> 
> For some of us, that particular aspect might be twice as important than all of the others in the pro/con list. So, maybe that was intentional.


:laugh:


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## ErinH (Feb 14, 2007)

rton20s said:


> In the "Conclusions" section, under the TM65 MkII, "+more affordable" is listed twice.
> 
> For some of us, that particular aspect might be twice as important than all of the others in the pro/con list. So, maybe that was intentional.


As Alan Jackson said, too much of a good thing... is a good thing.


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## ErinH (Feb 14, 2007)

Justin Zazzi said:


> Yep, the suspension on the TM65ii as very asymmetrical. I went full retard and destroyed a driver in the process to learn more about that specifically


heh... I can relate. 

Yea, given the extreme apparent offset I was having trouble deciding if it was more asymmetry or just offset. Thanks for clearing that up. I am surprised you were able to get it to resolve. I bet that was a pretty hair raising test.


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## ErinH (Feb 14, 2007)

Justin Zazzi said:


> Yes I do, and I didn't think to post them but I will.


Great.




Justin Zazzi said:


> This is incorrect. The trace I overlaid on top of the TM65ii's frequency response was made in the near field and smoothed to 24dB/octave. I did this on purpose to try and match the conditions that the manufacturer stated was used to make their frequency response. You can see the black trace in that graphic (near field) is different from any of the traces in the polar measurements I made (in the far field). I tried to mention this in the paragraph near that graphic but my wording was not very clear. I will try to make that more clear.


Ok. I admittedly was reading the pdf from my iphone so I had to do a LOT of pinch and zoom and going back and forth so I obviously dropped the ball. I went back and read and yep… totally my oversight. Apologies.






Justin Zazzi said:


> Very good catch. I mistakenly reported a window length of 2.5ms but the window is actually 3.0ms which corresponds to a frequency resolution of 333hz and this is where I stitched the nearfield and farfield responses together. As for the trough in both sets of far field measurements, I will look into that. It could always be an anomaly in my setup and if it is I would like to find the flaw in my method. Below are the nearfield traces (for all frequencies) overlaid on the far-field traces (still 3.0ms windowed and stopping at 333hz). What do you see below?


Ok. The difference of 2.5ms vs 3.0ms is negligible. I looked at your results and still wonder if merging the responses higher – maybe 800hz – might be more accurate? To be honest, the trough stands out to me. I wouldn’t expect to see that and I have to wonder if it’s the baffle’s influence given the shape. It could very well be the driver, though. Unfortunately the only way I can think to ‘vet’ this would be to simulate using EDGE (which is free and easy to use) and/or to compare against a driver tested by another source who you trust implicitly as a ‘baseline’ of sorts for your measurements. Merging NF/FF is an art as much as it is a science. As you know there is a high-frequency limit based on the effective radius of the driver (I think I provided an aRTA white paper in your other thread a few months back that delves in to this topic further than my memory serves) and the lower limit is typically based on the impulse window. Between those two bounds you have some lee-way. I wound up doing some iterative testing, placing the mic at distances of a few centimeters, out to a meter in a few different steps along the way so I could see the progression of the high-frequency wave development and then home in on a more repeatable method. 






Justin Zazzi said:


> I was using 70% of BL since this is what was used by Stereo Integrity when quoting the Xmax value that is published in their literature and on their website (searching for a 30% decay in BL strength when running a finite element analysis with a program such as FEMM). My intention was to show that the published value for Xmax is not unreasonable given the tools that the manufacturer used to determine it, however there are more precise methods to get a better value. Unfortunately, the better tools (like the Klippel distortion analyzer) are tens of thousands of dollars.
> 
> Exactly. Many methods can be used to measure Xmax since it is poorly defined. I tried to make it clear which method the manufacturers used, which method I used, and why there was a difference. It is not difficult to change the procedure in application note 4 to find 20% THD, however it would require running the test with different protection limits that would have a higher chance of damaging the woofer since it would have to be stressed harder. The key point I was trying to make in all of this is that the BL curve alone doesn't tell the whole story since the suspension can contribute just as much, if not more, acoustic distortion to our ears.


Understood. I didn’t see where you stated why you chose to use two different THD limits, at least not explicitly explaining to readers that you were both cognizant of this and doing so intentionally. But I understand where you’re coming from. 






Justin Zazzi said:


> I do have all of this information too, however the depth of detail has to stop somewhere right? I felt this much information would be less valuable to this audience and I didn't feel comfortable enough explaining it in a way that wouldn't make it feel more complicated. If you're interested in pursuing this further lets chat somewhere on the side until I have a better understanding and can present it more clearly.


Absolutely. However, when discussing factors leading to xmax determination even Klippel focuses on Motor, Suspension and Inductance. They are all equally important toward telling the story. It’s common practice to see this set of data in this context. Voice Coil Magazine’s reports are a fine example. If you didn’t publish it simply due to the complexity then… heck, man… how many of us really even know what Bl or Cms really is anyway. I’m sure one or two more data points won’t send people over the edge. Lol. Post it up and let’s go through it as a group so we can all learn. That’s ultimately what we are here for. I’ll explain what I can… we can ask Andy to do so as well.






Justin Zazzi said:


> I am curious about the work you refer to from Geddes. Where can I find this?


I did a 5 minute search but didn’t come up with what I was looking for. Maybe it wasn’t Geddes’ work. But, I’ve talked to Patrick Turnmire at Red Rock (Patrick is a speaker design and Klippel guru) and he was the one who first alerted me to this back when I first started testing. I’ve seen it referenced since then. But best I could come up with was this:
https://www.axiomaudio.com/blog/distortion

If I have time to really dig in to white papers (which I don’t foresee) I’ll post back. I may have better luck digging through my old threads here, though.







Justin Zazzi said:


> The distortion components are based on voltage (or excursion) but also frequency. The way the Klippel dB-Lab software is laid out makes this impossible to see in a single chart and requires correlating data from one graph to another while simultaneously changing display settings which is not easy to display or explain. If you know of an easy way to display to view this, I would love to hear about it.


Ok. I looked at the AN and the only frequency plot it showed was for determination of Fs. The other plots were voltage vs distortion. Which I assume is what you’re talking about. If you don’t have the means to (easily) provide it then no worries. I was just hopeful maybe they also provided the data in another output window that wasn’t provided in the example in the AN. 




Justin Zazzi said:


> I believe I have what you are looking for. This requires setting the limits of acceptable deviation for each of these parameters though (like 82% for BL, etc). However we would have to agree on what limits to use for BL, Kms, and Le(x). I do not see a section in that window showing excursion limits based on Le(I), but the other windows show Le(I) contributes nearly zero distortion to either woofer.


The limits are defined in their literature. Here’s an example:
https://www.klippel.de/fileadmin/kl...plication_Notes/AN_05_Displacement_Limits.pdf

At the end it provides the values for 10% THD: 
Bl = 82%, Cms = 75%, Zmax = 10%, Doppler = 10%






Justin Zazzi said:


> The distortion plots from the Klippel X10 module only go up to 320 hz since that is the limit I set in consideration of the time required to keep going. I don't believe I have what you're looking for here.


Hmph. *kicks rocks*






Justin Zazzi said:


> Understood and greatly appreciated!


For sure. I appreciate you being receptive to feedback. I understand how much of a PITA this stuff is and it’s easy to feel ‘attacked’ when people express concerns or have questions about the test. I had to have a few conversations with people on the phone because they were very rude with their replies so I try my hardest to not come off in a negative manner. Ultimately, we are all here to learn. With contributions like yours and open discourse, we all benefit. So, again, kudos to you for taking this on.


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## Electrodynamic (Nov 27, 2007)

Thanks for publishing the data Justin. It was a pleasure working with you during the measurement process...especially us adamantly giving you the green-light to destroy a driver to see if it was the spider or the surround that was responsible for the non-linearity. AFAIK our TM65 mkII is the first driver with this exact S surround geometry to be measured by Klippel so it was/is very educational and we are working on a revised, more linear, design because of your data. Thanks again Justin.


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## SQLnovice (Jul 22, 2014)

Now I want to sell my mid-bass and save up for a pair of GB's. Justin, thanks for the time you put into this.


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## Justin Zazzi (May 28, 2012)

Hey there Nick,

I really enjoyed the collaboration too and I'm glad we all learned something interesting. I was hoping you might mention the destruction testing we did so I could share the picture below. Don't try this at home kids!


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## Justin Zazzi (May 28, 2012)

Ok, so it turns out I don't have the impedance sweeps entirely. I was following Klippel's application note 25 (linked below) which says the maximum frequency for the linear parameter modeling test should be about 20x the resonant frequency of the driver, in order to get the best curve fit for mathematical models which is what Klippel's dB-Lab software is based upon. So for both the GB60 and the TM65ii, the high frequency limit is 1,200hz and I don't have any impedance sweep data above that. In the future I will have to get this data using my Dayton DATSv2 system instead.
http://www.klippel.de/know-how/literature/application-notes.html



ErinH said:


> Ok. The difference of 2.5ms vs 3.0ms is negligible. I looked at your results and still wonder if merging the responses higher – maybe 800hz – might be more accurate? To be honest, the trough stands out to me. I wouldn’t expect to see that and I have to wonder if it’s the baffle’s influence given the shape. It could very well be the driver, though. Unfortunately the only way I can think to ‘vet’ this would be to simulate using EDGE (which is free and easy to use) and/or to compare against a driver tested by another source who you trust implicitly as a ‘baseline’ of sorts for your measurements. Merging NF/FF is an art as much as it is a science. As you know there is a high-frequency limit based on the effective radius of the driver (I think I provided an aRTA white paper in your other thread a few months back that delves in to this topic further than my memory serves) and the lower limit is typically based on the impulse window. Between those two bounds you have some lee-way. I wound up doing some iterative testing, placing the mic at distances of a few centimeters, out to a meter in a few different steps along the way so I could see the progression of the high-frequency wave development and then home in on a more repeatable method.


Oh right, I've had EDGE and Svante Granqvist's other programs in my "incoming acoustics" folder forever. He has a fantastic suite of tools available for free on his website Tolvan Data

Using EDGE, I modeled the baffle as best I could (4ft by 6ft with one speaker placed 2ft from each edge) and the resulting transfer function (image below) doesn't show a singular valley in the midbass from about 300hz to 1khz like we are seeing in my polar measurements. There are effects in that region, but there are many peaks and valleys bunched up that don't seem to match what we are seeing with my measurements.












ErinH said:


> Absolutely. However, when discussing factors leading to xmax determination even Klippel focuses on Motor, Suspension and Inductance. They are all equally important toward telling the story. It’s common practice to see this set of data in this context. Voice Coil Magazine’s reports are a fine example. If you didn’t publish it simply due to the complexity then… heck, man… how many of us really even know what Bl or Cms really is anyway. I’m sure one or two more data points won’t send people over the edge. Lol. Post it up and let’s go through it as a group so we can all learn. That’s ultimately what we are here for. I’ll explain what I can… we can ask Andy to do so as well.


Very well, but I wouldn't directly ask Andy to help for at least the next two weeks since I'm sure he is busy preparing for the CES in Las Vegas. I can help explain these things as well, but I'm interested in what you see too.

The inductance for the GB60 is below:









The inductance for the TM65ii is below:












ErinH said:


> I did a 5 minute search but didn’t come up with what I was looking for. Maybe it wasn’t Geddes’ work. But, I’ve talked to Patrick Turnmire at Red Rock (Patrick is a speaker design and Klippel guru) and he was the one who first alerted me to this back when I first started testing. I’ve seen it referenced since then. But best I could come up with was this:
> https://www.axiomaudio.com/blog/distortion
> 
> If I have time to really dig in to white papers (which I don’t foresee) I’ll post back. I may have better luck digging through my old threads here, though.


Thanks for the link, even though it's not exactly what you were looking for. The project results are interesting. My initial thought is even if the listeners cannot notice 20% distortion (or more) in the lower frequencies, the woofers would have to be pushed so hard to reach that amount of distortion that the physical longevity of the woofers would concern me. This is interesting to think about.


ErinH said:


> Ok. I looked at the AN and the only frequency plot it showed was for determination of Fs. The other plots were voltage vs distortion. Which I assume is what you’re talking about. If you don’t have the means to (easily) provide it then no worries. I was just hopeful maybe they also provided the data in another output window that wasn’t provided in the example in the AN.


Yeah the data is provided as either %distortion vs frequency vs voltage, or as displacement(x) vs voltage vs frequency and they are both on separate charts that require changing the display settings to view each one correctly so they can't even be viewed at the same time. I cannot find an option for %distortion vs frequency vs displacement(x) on the same chart. It's maddening, and I plan to ask Wolfgang Klippel about it when I attend training at his facility in Germany soon.


ErinH said:


> The limits are defined in their literature. Here’s an example:
> https://www.klippel.de/fileadmin/kl...plication_Notes/AN_05_Displacement_Limits.pdf
> 
> At the end it provides the values for 10% THD:
> Bl = 82%, Cms = 75%, Zmax = 10%, Doppler = 10%


*Below is for the GB60. Notice the limits for BL and XC are fairly similar.*











*Below is for the TM65ii. Notice the limit for X C (suspension compliance) is the limiting factor.*


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## Mike-G (Dec 25, 2008)

Granted, I am a novice and do not have either of these drivers (not that I haven't wanted them) but this write up was very interesting to read and learn more about different drivers and what all the specs mean to performance. Thank you very much for doing this!

I wonder how far off the GS series from Audiofrog would compare to the SI or to the GB series?


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## quickaudi07 (May 19, 2010)

Very educational review Justin.

Thank you so much and for others to put in effort and giving your own statement and experience.


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## 156546 (Feb 10, 2017)

One thing that sort of stands out in all of this is the fact that measuring speakers and interpreting those measurements isn't a simple matter. It takes study and practice. As measurement tools and practices evolve, those tools sometimes make it easier to see what we had to figure out in other ways in the past.

Prior to Klippel, it was certainly possible to make a great speaker and characterize its performance, but it was quite a bit more difficult to separate distortion components into distortion caused by the motor and distortion caused by the suspension. In a nut shell, this is what the Klippel machine does. 

No matter the tool used to make measurements of any sort, the first thing one has to do is ask, "does this measurement make sense?"


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## Holmz (Jul 12, 2017)

GotFrogs said:


> ...
> No matter the tool used to make measurements of any sort, the first thing one has to do is ask, "does this measurement make sense?"


Why am I thinking about pilots doing that when they look at their gauges?


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## ohlwiler (Nov 6, 2013)

The signal to noise ratio can be kind of low sometimes on diyma but investigations like these is what keeps me glued to my seat. Great data Justin. Maybe the SI TM3 will incorporate a more traditional surround and will produce a stellar driver.


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## quickaudi07 (May 19, 2010)

New design will be awesome if the SI drivers

Sent from my ONEPLUS A3000 using Tapatalk


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## 1fishman (Dec 22, 2012)

Where's all the posts?


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## GEM592 (Jun 19, 2015)

Housecleaning


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## 1fishman (Dec 22, 2012)

GEM592 said:


> Housecleaning


So you think this was intentional? 

I was reading page 1, clicked on page 2 and nothing. Really nothing was even controversial, just a bunch of really good perspectives.


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## Justin Zazzi (May 28, 2012)

It's like someone is trying as hard as they can to kill this place while making it look accidental. I'm really tired of it.


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## Dan750iL (Jan 16, 2016)

They've been having issues with content disappearing for a little over a week now. It all came back then vanished again. Pretty sure it's just a technical glitch with the board. Hopefully all of the content will be back.


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## ErinH (Feb 14, 2007)

Definitely not 'housecleaning' so you can end the conspiracies there. I don't know wtf the problem is but it's not just affecting this thread. It's site wide and has been happening off and on since the new owners took over. There's plenty of other threads. See here:
http://www.diymobileaudio.com/forum...rt/401121-many-my-posts-threads-now-gone.html


I'd encourage you guys to post your complaints in that thread. Try not to take this thread about those issues, though, because (assuming it does) when it comes back it wouldn't make any sense to have thirty posts about missing posts.


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## 1fishman (Dec 22, 2012)

It's all back, Magic 

Thanks to however fixed this. 
Oh yeah, and Zazzi too. Great job


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## Justin Zazzi (May 28, 2012)

I have moved and so I welcome any new discussion at my new home at thread below:






Report: Audiofrog GB60 and Stereo Integrity TM65 mkII


This was originally posted on DIYMA on January 3rd, 2018:  This is a comparison between the two 6.5" woofers in the title using a Klippel Distortion Analyzer while I was working at Eminence Speaker Company at the time. This was a ton of fun to make and I'm very thankful to the folks to...



www.caraudiojunkies.com


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## 619Tundra (Sep 24, 2020)

The cardborad packaging is easy to recycle. Lol.


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