I understand and will post link later as from Android.
The notation was made in a post with the correlation.
Of course they are using the seos 12, 15 and 24 on AVRS forums that they are CD so its not the same scenario but I thought the comments was interesting from an experienced designer who ahs trialled more then one woofer and the subjective comment aligned with those here on the AE15M.
I just don't get it that a lower distortion driver was not as suitable subjectively.
The link has distortion plots and a full set of power response curves.
http://www.avsforum.com/t/1457166/s-e-o-s-r-mega-build/1110
The notation was made in a post with the correlation.
Of course they are using the seos 12, 15 and 24 on AVRS forums that they are CD so its not the same scenario but I thought the comments was interesting from an experienced designer who ahs trialled more then one woofer and the subjective comment aligned with those here on the AE15M.
I just don't get it that a lower distortion driver was not as suitable subjectively.
The link has distortion plots and a full set of power response curves.
http://www.avsforum.com/t/1457166/s-e-o-s-r-mega-build/1110
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Folks generally like their colors, foods, etc., 'rich', so it seems reasonable that they want their sound that way also, especially since recordings rarely [if ever] completely capture all the 'texture' of a sonic event.
GM
Interesting point, much appreciated, and something to think about.
My evolution towards the Altec/GPA 416 Alnico was the result of direct comparison with the JBL 2226 (after adjustments to the crossover and time-alignment of the AH425). I was really surprised; I expected the two drivers to sound very similar, and they didn't. The biggest differences were in the piston-band region, which shouldn't have happened at all (measured efficiencies of the two drivers are within 0.5 dB of each other, less than typical manufacturing variation).
Based on my enthusiastic report about the GPA 416 Alnico, Gary Dahl (who already had a pair of TD15M & AH425 speakers) not only ordered a pair of GPA 416's, but a pair of 515 Alnico's as well. Gary never does anything halfway.
I've not done the direct comparison between the AE TD15M, GPA 416 Alnico, and GPA 515 Alnico, but Mr. Dahl has, and I trust his listening impressions. Gary Pimm (of Portland) recently heard the new system, and liked what he heard. Both Gary's have been personal friends for more than ten years, have heard my system here in Colorado, so they know the sound I'm aiming for.
I'm strongly considering a dual-416 version of Gary Dahl's system, with an active subwoofer yet to be determined.
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Hello Lynn, nice to see you back.
2.5 way crossover or both driver playing up to the horn?
To continue (previous post timed out), the closed-box system has its own 2nd-order highpass function around 60 Hz or so, and the higher-Q alignment has a subtle advantage in decreased excursion below the corner frequency.
All the left and right subwoofer does is operate between 20~25 Hz and 50~60 Hz, depending on the desired degree of overlap. Each subwoofer has its own highpass filter adjustment, since room location affects the response in the 20~100 Hz region, and it's possible the amount of sub and woofer overlap may be different between left and right channels.
All the left and right subwoofer does is operate between 20~25 Hz and 50~60 Hz, depending on the desired degree of overlap. Each subwoofer has its own highpass filter adjustment, since room location affects the response in the 20~100 Hz region, and it's possible the amount of sub and woofer overlap may be different between left and right channels.
Hi Lynn,
I talked to Gary Pimm and a few of his friends at Bud Purvine's house after they came from Gary Dahl's place. I must say that they were "quite impressed" with what they had heard! I haven't heard them myself, so I won't go any further into it, other than I really want to hear them myself!
Best Regards,
TerryO
Gary Dahl, Gary Pimm, and I have a good collaboration going back a decade or more. Gary Dahl is classical musician who conducts and plays, and has a keen sense of timbre, tonality, and musical "rightness". If he says the cello and piano sounds "right", I trust his musical impressions.
I've heard Gary Pimm's system lots of times, and we've done some fun experiments with auditioning various DIY projects. He's the master of the precise A/B comparison, and as a Tektronix guy, knows measurements backwards and forwards. I get all kinds of good ideas from these guys. I'd much rather collaborate with the two Gary's, Martin Seddon, Bjorn Kolbrek, and others than work alone.
It's unfortunate that a 100~700 Hz bass horn is so damn big; there's just no way it can work with the living room I have. The attraction of bass horn tonality and dynamics is part of the reason I'm thinking of dual 15" drivers ... an efficiency gain of 3 dB and headroom increase of 6 dB may not sound like much, but it gets direct-radiators closer to what bass horns can do.
One of the problems with an enclosure the size of an Onken or an Altec Model 19 is controlling interior-volume box modes and panel resonances. The bigger the box, the harder these are to control. Also, as the box gets bigger, the first modes appear at lower frequencies, thanks to larger interior distances and larger panels.
Gary Dahl's compact closed boxes reduce the volume to about 1/3 that of the traditional Altec vented box, and driver excursion does not increase below F3. This is helpful with an underhung voice coil, which has low distortion as long as the VC stays in the magnetic gap. The 416 Alnico effectively becomes a bass-mid driver, with a bit more than a decade of usable bandwidth, and covering the most important region of the musical spectrum.
The below-60 Hz region is relegated to 2 or 4 active subwoofers, although I prefer to leave mono-sum bass to movie soundtracks, and use stereo bass for 2-channel sources.
I've heard Gary Pimm's system lots of times, and we've done some fun experiments with auditioning various DIY projects. He's the master of the precise A/B comparison, and as a Tektronix guy, knows measurements backwards and forwards. I get all kinds of good ideas from these guys. I'd much rather collaborate with the two Gary's, Martin Seddon, Bjorn Kolbrek, and others than work alone.
It's unfortunate that a 100~700 Hz bass horn is so damn big; there's just no way it can work with the living room I have. The attraction of bass horn tonality and dynamics is part of the reason I'm thinking of dual 15" drivers ... an efficiency gain of 3 dB and headroom increase of 6 dB may not sound like much, but it gets direct-radiators closer to what bass horns can do.
One of the problems with an enclosure the size of an Onken or an Altec Model 19 is controlling interior-volume box modes and panel resonances. The bigger the box, the harder these are to control. Also, as the box gets bigger, the first modes appear at lower frequencies, thanks to larger interior distances and larger panels.
Gary Dahl's compact closed boxes reduce the volume to about 1/3 that of the traditional Altec vented box, and driver excursion does not increase below F3. This is helpful with an underhung voice coil, which has low distortion as long as the VC stays in the magnetic gap. The 416 Alnico effectively becomes a bass-mid driver, with a bit more than a decade of usable bandwidth, and covering the most important region of the musical spectrum.
The below-60 Hz region is relegated to 2 or 4 active subwoofers, although I prefer to leave mono-sum bass to movie soundtracks, and use stereo bass for 2-channel sources.
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Over the years I have learned a few things in regards to audio reproduction. One of them is that you can never please everyone. Regardless of that, my goal has always been the same: Make drivers that will provide the most accurate reproduction possible.
It is easy to look at different orders of harmonic distortion and see where they come from. Klippel does a good job of analyzing these distortions. Through this analysis we can see the causes for the distortion and find a way to eliminate it. I have tried to address all aspects in our drivers while many others address only few. Great effort has been put into creating a low distortion motor system. While many have done the same work to create symmetrical Bl curves, most stop there. We have gone further to reduce inductance variance and reduce flux modulation as well. These factors are the main cause of odd order distortions in the motor. Many go and work with cone materials and surrounds that eliminate physical resonances. We have gone further to address distortion created in the dustcap resonance by eliminating it, and further working to apply damping to the cone and surround as well. There is no doubt that this creates a driver that has a unique sound characteristic as others are simply not addressing all these issues. That sound is as true to the original recording as we can possibly get. Our goal is to not add any sound to the recording. There is no additional warmth or tonality added to the signal. What goes in comes back out.
Some are not used to this and I would say a small amount actually dislike this. Drivers that have additional distortions and resonances can sound different. Much like adding reverb to a vocal, these resonances and distortions add to the recording. The same on the recording end. Different microphones can add their own character to the signal as well. Adding these distortions and resonances can on occasion help mask some things that are unpleasant. A very bad PA system can mask a bad vocal by making it impossible to accurately hear the details of what are being sung poorly.
This however is not accurate reproduction and not the goal we set out for. We believe the recording artist and engineer have the responsibility of creating the recording as they believe it should be heard. We then produce drivers to accurately reproduce that recording as best possible.
With the comparison between the 416 and the TD15M, there are a few things that greatly stand out. I do not have comparable measurements but do on the 414 and TD12M which illustrates some large differences.
The GPA/Altec 414 actually has probably the highest Le(x) variance of any driver I have seen. The coil in a woofer is essentially an inductor. When it is around the steel pole it has higher inductance, acting as an iron core inductor. As the coil comes forward and out of the gap, it begins to act more as air core and inductance lowers. At 1KHz, the impedance varies from 15ohm on the outward stroke to 25ohm on the inward stroke with a range of +/-5mm. As you are playing low frequency information and the driver starts moving, the upper end response will vary with every inward and outward stroke of the driver. Not only will the response magnitude be changing, but the impedance actually changes altering the power delivered to the driver. This is very significant in terms of distortion. It is also very significant with a crossover as the response and phase is continually changing with every stroke. With passive crossovers it is critical. The crossover values correspond to the impedance curve. As impedance changes so does the effective crossover point determined by those components. The end result is a varying response curve, varying lowpass frequency, and changing phase relationship between drivers.
https://sites.google.com/site/drive...nd-75-1558se/gpa-altec-414/le-x/Le(x)_5mm.PNG
Compare this now to the TD12M. Measured at 7mm, there is no apparent change in the impedance curve even up to 20KHz with +/-7mm excursion. The copper sleeve on the pole has forced it to act as an air core at all excursions. It no longer even "sees" the pole as an iron core at all. This means current applied to the coil is the same at rest as it is at +/-7mm. The issues with phase and frequency response have been eliminated. The distortions due to changing inductance are also eliminated. Crossover values calculated based on small signal parameters are now accurate for large signal parameters as well. Resultant 3rd harmonic distortion is over 10dB lower in the 200hz-1KHz range as well.
https://sites.google.com/site/drive...5-1558se/ae-speakers-td12m/le-x/Le(x)_7mm.PNG
We can start to investigate just what this extra distortion being added is. Taking a look at the GPA414 with a 500hz multi tone signal applied at 100db in comparison to the TD12M. At 700hz you can see the signal is about 15dB higher with the GPA414 than the TD12M. You can also see a large amount of signal appear at about 1600hz, nearly 20dB more than in the TD12M. These are not fundamental tones that have been applied to the driver. They are created IN the driver itself.
https://sites.google.com/site/drive...n-linear-distortion/multitone_500hz_100dB.PNG
https://sites.google.com/site/drive...n-linear-distortion/multitone_500hz_100dB.PNG
We can investigate the same with 2 tone signals applied at 300hz and 1100hz. At many points the 414 is creating 10-15dB more signal that was never applied to the driver.
https://sites.google.com/site/drive...c-414/non-linear-distortion/twotone_100dB.PNG
https://sites.google.com/site/drive...td12m/non-linear-distortion/twotone_100dB.PNG
While there is much more to audible distortion than just THD, this can be seen as a good generalization also in the THD measurements of the driver with a 150hz tone applied. The 414 has measured 2.775% distortion while the TD12M is measured at .285% distortion, lower by a factor of 10x!
https://sites.google.com/site/drive...14/non-linear-distortion/tone_150hz_100dB.PNG
https://sites.google.com/site/drive...2m/non-linear-distortion/tone_150hz_100dB.PNG
There is no doubt at all that this extra distortion measurable by simple single or multi tone bursts is going to create an audible effect. It could be creating the additional "warmth" or "tonality" that some have mentioned. What it is not doing though is accurately reproducing the signal it is supposed to. It is possible to add something to some recordings that could by theory make them sound more warm if the recording was extremely dry. The problem comes in with reproducing a recording that is already accurately recorded with proper amounts of reverb and good tonality. Adding more to those recordings then makes it sound muddy and inarticulate. No woofer can ideally add anything to a good recording done in a concert hall and IMO it should never attempt to.
The woofers we make are often very revealing to recordings. One of the most common comments I hear is "I am hearing things I never heard before." I have had more than one person state they had relisten to every album they own to see what else they have been missing. The drawback to that is that it is also very revealing for bad recordings. Nothing is masked or hidden. Many people are not used to that.
That all said, power response is a big factor as well. Most measurements are taken straight on axis. If we heard only the direct sound, that would be ideal. In reality though, we hear much of the off axis sound that is reflected to us and that has a lot to do with the perceived overall sound also. When we remove physical resonances in the driver, this actually has a lot of effect in the power response as well and can have a lot of perceived difference.
It is easy to look at different orders of harmonic distortion and see where they come from. Klippel does a good job of analyzing these distortions. Through this analysis we can see the causes for the distortion and find a way to eliminate it. I have tried to address all aspects in our drivers while many others address only few. Great effort has been put into creating a low distortion motor system. While many have done the same work to create symmetrical Bl curves, most stop there. We have gone further to reduce inductance variance and reduce flux modulation as well. These factors are the main cause of odd order distortions in the motor. Many go and work with cone materials and surrounds that eliminate physical resonances. We have gone further to address distortion created in the dustcap resonance by eliminating it, and further working to apply damping to the cone and surround as well. There is no doubt that this creates a driver that has a unique sound characteristic as others are simply not addressing all these issues. That sound is as true to the original recording as we can possibly get. Our goal is to not add any sound to the recording. There is no additional warmth or tonality added to the signal. What goes in comes back out.
Some are not used to this and I would say a small amount actually dislike this. Drivers that have additional distortions and resonances can sound different. Much like adding reverb to a vocal, these resonances and distortions add to the recording. The same on the recording end. Different microphones can add their own character to the signal as well. Adding these distortions and resonances can on occasion help mask some things that are unpleasant. A very bad PA system can mask a bad vocal by making it impossible to accurately hear the details of what are being sung poorly.
This however is not accurate reproduction and not the goal we set out for. We believe the recording artist and engineer have the responsibility of creating the recording as they believe it should be heard. We then produce drivers to accurately reproduce that recording as best possible.
With the comparison between the 416 and the TD15M, there are a few things that greatly stand out. I do not have comparable measurements but do on the 414 and TD12M which illustrates some large differences.
The GPA/Altec 414 actually has probably the highest Le(x) variance of any driver I have seen. The coil in a woofer is essentially an inductor. When it is around the steel pole it has higher inductance, acting as an iron core inductor. As the coil comes forward and out of the gap, it begins to act more as air core and inductance lowers. At 1KHz, the impedance varies from 15ohm on the outward stroke to 25ohm on the inward stroke with a range of +/-5mm. As you are playing low frequency information and the driver starts moving, the upper end response will vary with every inward and outward stroke of the driver. Not only will the response magnitude be changing, but the impedance actually changes altering the power delivered to the driver. This is very significant in terms of distortion. It is also very significant with a crossover as the response and phase is continually changing with every stroke. With passive crossovers it is critical. The crossover values correspond to the impedance curve. As impedance changes so does the effective crossover point determined by those components. The end result is a varying response curve, varying lowpass frequency, and changing phase relationship between drivers.
https://sites.google.com/site/drive...nd-75-1558se/gpa-altec-414/le-x/Le(x)_5mm.PNG
Compare this now to the TD12M. Measured at 7mm, there is no apparent change in the impedance curve even up to 20KHz with +/-7mm excursion. The copper sleeve on the pole has forced it to act as an air core at all excursions. It no longer even "sees" the pole as an iron core at all. This means current applied to the coil is the same at rest as it is at +/-7mm. The issues with phase and frequency response have been eliminated. The distortions due to changing inductance are also eliminated. Crossover values calculated based on small signal parameters are now accurate for large signal parameters as well. Resultant 3rd harmonic distortion is over 10dB lower in the 200hz-1KHz range as well.
https://sites.google.com/site/drive...5-1558se/ae-speakers-td12m/le-x/Le(x)_7mm.PNG
We can start to investigate just what this extra distortion being added is. Taking a look at the GPA414 with a 500hz multi tone signal applied at 100db in comparison to the TD12M. At 700hz you can see the signal is about 15dB higher with the GPA414 than the TD12M. You can also see a large amount of signal appear at about 1600hz, nearly 20dB more than in the TD12M. These are not fundamental tones that have been applied to the driver. They are created IN the driver itself.
https://sites.google.com/site/drive...n-linear-distortion/multitone_500hz_100dB.PNG
https://sites.google.com/site/drive...n-linear-distortion/multitone_500hz_100dB.PNG
We can investigate the same with 2 tone signals applied at 300hz and 1100hz. At many points the 414 is creating 10-15dB more signal that was never applied to the driver.
https://sites.google.com/site/drive...c-414/non-linear-distortion/twotone_100dB.PNG
https://sites.google.com/site/drive...td12m/non-linear-distortion/twotone_100dB.PNG
While there is much more to audible distortion than just THD, this can be seen as a good generalization also in the THD measurements of the driver with a 150hz tone applied. The 414 has measured 2.775% distortion while the TD12M is measured at .285% distortion, lower by a factor of 10x!
https://sites.google.com/site/drive...14/non-linear-distortion/tone_150hz_100dB.PNG
https://sites.google.com/site/drive...2m/non-linear-distortion/tone_150hz_100dB.PNG
There is no doubt at all that this extra distortion measurable by simple single or multi tone bursts is going to create an audible effect. It could be creating the additional "warmth" or "tonality" that some have mentioned. What it is not doing though is accurately reproducing the signal it is supposed to. It is possible to add something to some recordings that could by theory make them sound more warm if the recording was extremely dry. The problem comes in with reproducing a recording that is already accurately recorded with proper amounts of reverb and good tonality. Adding more to those recordings then makes it sound muddy and inarticulate. No woofer can ideally add anything to a good recording done in a concert hall and IMO it should never attempt to.
The woofers we make are often very revealing to recordings. One of the most common comments I hear is "I am hearing things I never heard before." I have had more than one person state they had relisten to every album they own to see what else they have been missing. The drawback to that is that it is also very revealing for bad recordings. Nothing is masked or hidden. Many people are not used to that.
That all said, power response is a big factor as well. Most measurements are taken straight on axis. If we heard only the direct sound, that would be ideal. In reality though, we hear much of the off axis sound that is reflected to us and that has a lot to do with the perceived overall sound also. When we remove physical resonances in the driver, this actually has a lot of effect in the power response as well and can have a lot of perceived difference.
Hello John,
JBL has made quite a few available lately:
1501al-2
1501al-1
2216Nd
100fe-12 (this one is a 10")
Regarding distortion comparison, it looks like the 414 has indeed a lot more 2nd and 3rd order distortion (but the latter could be reduced with current drive for example, or maybe with the alnico version if this is the ferrite), but it also look like the TD12M has a bit more of the higher order ones...
Would you have klippel measurements of your drivers that you could publish?
JBL has made quite a few available lately:
1501al-2
1501al-1
2216Nd
100fe-12 (this one is a 10")
alnico or ferrite version?
Regarding distortion comparison, it looks like the 414 has indeed a lot more 2nd and 3rd order distortion (but the latter could be reduced with current drive for example, or maybe with the alnico version if this is the ferrite), but it also look like the TD12M has a bit more of the higher order ones...
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Hi John,
A point of interest is you state the GPA/Altec 414 was tested at +/-5mm. Both the old data from Altec found here and the data from GPA here shows the 414 having an X-max of 4mm.
With the 414 having an underhung voice coil +/-5mm would be pushing the voice coil out of the gap essentially operating the driver outside of it's design window.
Gary
A point of interest is you state the GPA/Altec 414 was tested at +/-5mm. Both the old data from Altec found here and the data from GPA here shows the 414 having an X-max of 4mm.
With the 414 having an underhung voice coil +/-5mm would be pushing the voice coil out of the gap essentially operating the driver outside of it's design window.
Gary
This was all tested by Brandon Thill. Le(x) was tested at +/-5mm as you state. Regardless, 1mm is going to have very little effect on the Le(x) curve. If you really wanted you could plot all points as in Klippel data. What you will see is a typical S shape curve that drivers without any shorting rings have. The fact that this is an underhung motor and still suffers such non-linearity in the Le(x) is a little strange as the core inside the coil shouldn't change with excursion. The test of 5mm Xmax for the Le(x) has no bearing on all the other measurements though.
The measured change in inductance for the GPA 414 (Alnico 16-ohm) is more than a little puzzling.
An underhung VC is completely within a somewhat deeper gap where the field lines are straight; as long as it stays within the gap, change in both BL and Le should be very small. Once the VC leaves the gap, of course, all bets are off, since it enters the fringing-flux region that's outside the gap. As long as the field lines are straight and uniform, and the VC stays within this region, it's hard to imagine how BL and Le can significantly vary. That's why I'm puzzled by the measurement results ... unless the VC was driven out of the linear region (which is akin to driving a Class A amplifier into distortion).
An overhung VC is different, since a substantial part of the coil is always exposed to the fringing flux outside the gap. Sophisticated magnetic design is required to minimize changes in BL and Le in the linear-travel region of the voice coil, and I'm sure that Acoustic Elegance products are at the forefront of linear magnetic design. I'd also expect that the JBL 2226 reflects modern design practices, although probably not at the AE level.
The new speaker is intentionally flexible in the choice of 15" bass driver and 1.4" exit compression drivers. There are a number of professional drivers with efficiencies in the 97~100 dB/meter range that qualify: not just the Altec/GPA 414 (Alnico), but the AE TD15M, JBL 2226, Fane 15XB, Volt, B&C, and 18Sound, to name a few.
The AH425 works successfully with the Radian 745 as well as the Altec/GPA 288, as well as other 1.4" exit compression drivers (beryllium and aluminum diaphragms preferred).
An underhung VC is completely within a somewhat deeper gap where the field lines are straight; as long as it stays within the gap, change in both BL and Le should be very small. Once the VC leaves the gap, of course, all bets are off, since it enters the fringing-flux region that's outside the gap. As long as the field lines are straight and uniform, and the VC stays within this region, it's hard to imagine how BL and Le can significantly vary. That's why I'm puzzled by the measurement results ... unless the VC was driven out of the linear region (which is akin to driving a Class A amplifier into distortion).
An overhung VC is different, since a substantial part of the coil is always exposed to the fringing flux outside the gap. Sophisticated magnetic design is required to minimize changes in BL and Le in the linear-travel region of the voice coil, and I'm sure that Acoustic Elegance products are at the forefront of linear magnetic design. I'd also expect that the JBL 2226 reflects modern design practices, although probably not at the AE level.
The new speaker is intentionally flexible in the choice of 15" bass driver and 1.4" exit compression drivers. There are a number of professional drivers with efficiencies in the 97~100 dB/meter range that qualify: not just the Altec/GPA 414 (Alnico), but the AE TD15M, JBL 2226, Fane 15XB, Volt, B&C, and 18Sound, to name a few.
The AH425 works successfully with the Radian 745 as well as the Altec/GPA 288, as well as other 1.4" exit compression drivers (beryllium and aluminum diaphragms preferred).
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The best sounding live venue I'm been in was the Bayou in DC back around 1985. Massive horn setup mounted about the audience. All EV horns hung side by side, all listening was off axis and crystal clear. Second best was BB King in 1991 at the Windjammer in Westerly, RI. EV exponential mid and high horns, wall of direct radiators for bass. On axis was a bit over the top however off axis was excellent and the room was filled with clear, clean sound.
I stumbled upon this while searching for klippel-like data for AE drivers:
AudioRoundTable.com: Pi Speakers => 4012HO vs TD12S
AudioRoundTable.com: Pi Speakers => 4012HO vs TD12S
