Finished the xmax testing. Sort of. I had intended to use Klippel's Performance Based method for determining xmax as outlined here: http://www.klippel.de/pubs/Klippel papers/Assessment_of_Voice_coil_peak_displacement_XMAX_02.pdf But I ran into two roadblocks, the soundcard clips at around 19 volts, and the room totally dominates the harmonic distortion in the bass and inflates the figure. Basically the Klippel method is a two step test. First step is a simple harmonic distortion test by driving the speaker at its Fs to a given excursion and recording the THD, and stopping when THD equals 10%. The second step is to again drive the speaker at Fs then apply a second tone at 8.5 x Fs. This creates intermodular distortion, and again raise excursion until IMD equals 10%. Whichever step reached 10% at the lowest excursion defines the xmax. Now my hope was that most drivers would be limited by IMD which isn't to affected by room. As it turns out many are THD limited. But because of room effects the HD portion of the test is not absolutely accurate, only relatively accurate to the other drivers. Obviously we need an absolute number to since we are defining xmax from it. But I the tests do still have value as a relative comparison so I did them all anyway and posted them in the Xmax section.
Finally done! I have some drivers for sale too, barely used except for my testing: one B&C 12HPL76 $125 shipped, and a pair of FaitalPRO 12PR300 $250 shipped.
Finally done! I have some drivers for sale too, barely used except for my testing: one B&C 12HPL76 $125 shipped, and a pair of FaitalPRO 12PR300 $250 shipped.
I am curious to see if these measurements influence Lynn's decision on whether to use the 18Sounds 12NDA520 or the GPA 414. Or if there is something else that is a higher priority in his goals.
JohnJ's suggestion is a good one if it isn't a lot of work to do so. But it probably is.
I think the one thing that suprised me most was the GPA 414 Le(X) measurement. I thought the Alnico magnet and the underhung motor was suppose to linearize this effect. It doesn't look like it proved itself in those measurements. Now I am still pretty novice when reading measurements but I expected it to compete with the 12NDA520 & TD12M. Or I am misinterpreting the benefits of Alnico and underhung? (I am not trying to start a war, just trying to understand).
JohnJ's suggestion is a good one if it isn't a lot of work to do so. But it probably is.
I think the one thing that suprised me most was the GPA 414 Le(X) measurement. I thought the Alnico magnet and the underhung motor was suppose to linearize this effect. It doesn't look like it proved itself in those measurements. Now I am still pretty novice when reading measurements but I expected it to compete with the 12NDA520 & TD12M. Or I am misinterpreting the benefits of Alnico and underhung? (I am not trying to start a war, just trying to understand).
JoshK said:
A 16 ohm driver for any given design will always have more inductance and non-linear distortion at higher freq.s. An 8 ohm driver will have less. (..utilizing a common "voltage" amplifier.) A 4 ohm driver even less. etc..
Non-linear distortion from the GPA driver is worse, but it's still essentially below 1% for any given harmonic from 90 Hz up - at 100 db. I don't think that will be the limiting factor.
Its eff. is also decent for a 16 ohm driver, BUT it will require *2* in parallel to get where Lynn wants to go for a 1watt/1meter average. Of course a 2-driver vertical "array" can also reduce the rising higher freq. response as well - a *potential* bonus. Additionally using 2 will have a net effect of reducing non-linear distortion. It will double the price though.
On the other hand, he never said the project would be cheap. 
JoshK said:
I don't know that underhung motors help Le linearity as much as BL linearity? Guess it just goes to show what modern FEM modeling can do accomplish. There is *apparently* nothing spectacular in the FaitalPRO and Eminence motors, like shorting rings, but the performance is very good for both. Then again even though the GPA has quite a mountain in the breakup area, it's incredibly smooth. Just looking this driver you can see that a lot of attention was paid to the soft parts, and the response shows it.
The 18Sound really caught my attention last night with IMD results. Impressive. HD is good, but nothing incredible. But I weight IMD higher anyway, so...Too bad the response smoothness is mediocre. I guess JohnJ jsut needs to get around to putting an alnico motor on the TD12M. Lynn would like that. Personally I'd like to see at least a neo motor, lugging those heavy *** drivers around all the time got old.
augerpro said:
All Lambda motors were hand drawn on a napkin, I have never modeled them actually. There were 2 parts to the design that interplayed with each other and canceled each other bad aspects I learned once I pushed them to their limits. One was the extreme extension of the steel pole as that height had not been done prior to that time, and the other was the extra thickness of the copper faraday sleeve/ring. By taking the pole piece out of the motor so far it lowered the B loss of the copper sleeve in the gap. A win win I learned especially once the voice coil and top plate were made taller to match.
ScottG said:
He also needs to substantially increase the eff. of the driver - making more a of "mid" driver and less of a "bass" driver. (..or at least provide that as an option.)
Meeting those two requirements (alnico + eff.) and I think we would have a single driver winner.
All it takes is money.....................
It can be done BTW with a slight re-engineer of a couple things, but its an expensive big step to take as it requires some serious minimum orders for materials.
The TD12M looks really good, no question about it. There are some interesting aspects to Augerpro's testing, though ...
Look at the GPA/Altec 414 "multitone_500Hz_100dB" graphs and compare the region above 2 kHz to all the other drivers - both 12 and 15-inch sizes. Set aside the number (which is set by the loudest harmonics) and look at the high-order distortion spectra (above 2 kHz).
The Altec has surprisingly low high-order distortion in the frequency range where the ear is most sensitive to distortion. These HF artifacts are not affected by electrical low-pass filtering of the driver - the test stimulus has no content above 800 Hz, so everything above that is driver distortion + noise. Against expectation, it is better than the TD12M, and much better than the other 12" and 15" drivers.
414 Distortion
TD12M Distortion
It might be the underhung voice coil and/or the Alnico magnet which are responsible for the notably cleaner HF characteristic. There's your triode-distortion harmonic spectra right there. The other drivers have more "clutter" in the 2~5 kHz region, which reflects the presence of additional high-order IM distortion terms.
On the other hand, the AESpeakers TD12M has a much better LF distortion characteristic, as shown by the "tone_150Hz_100dB" graphic, which is most likely the result of the exceptionally good Le(x) of the TD12M. It walks away from all the other drivers below 300 Hz, and is really good above 300 Hz.
I'll be doing subjective listening of the 414/Alnico, TD12M, and the 18Sound 12NDA520, with a primary focus on naturalness of the midrange with solo voice and choral music. Although the nominal crossover is 800 Hz, I don't plan on slopes any steeper than 12 dB/octave, so the quality above 800 Hz remains important. This is the same philosophy as the Ariel - each driver has to be natural-sounding without high-slope filtering to reject breakup regions.
Other designers rely on digital and/or high-slope crossovers to get what they want, but that's not the sound I'm after.
Look at the GPA/Altec 414 "multitone_500Hz_100dB" graphs and compare the region above 2 kHz to all the other drivers - both 12 and 15-inch sizes. Set aside the number (which is set by the loudest harmonics) and look at the high-order distortion spectra (above 2 kHz).
The Altec has surprisingly low high-order distortion in the frequency range where the ear is most sensitive to distortion. These HF artifacts are not affected by electrical low-pass filtering of the driver - the test stimulus has no content above 800 Hz, so everything above that is driver distortion + noise. Against expectation, it is better than the TD12M, and much better than the other 12" and 15" drivers.
414 Distortion
TD12M Distortion
It might be the underhung voice coil and/or the Alnico magnet which are responsible for the notably cleaner HF characteristic. There's your triode-distortion harmonic spectra right there. The other drivers have more "clutter" in the 2~5 kHz region, which reflects the presence of additional high-order IM distortion terms.
On the other hand, the AESpeakers TD12M has a much better LF distortion characteristic, as shown by the "tone_150Hz_100dB" graphic, which is most likely the result of the exceptionally good Le(x) of the TD12M. It walks away from all the other drivers below 300 Hz, and is really good above 300 Hz.
I'll be doing subjective listening of the 414/Alnico, TD12M, and the 18Sound 12NDA520, with a primary focus on naturalness of the midrange with solo voice and choral music. Although the nominal crossover is 800 Hz, I don't plan on slopes any steeper than 12 dB/octave, so the quality above 800 Hz remains important. This is the same philosophy as the Ariel - each driver has to be natural-sounding without high-slope filtering to reject breakup regions.
Other designers rely on digital and/or high-slope crossovers to get what they want, but that's not the sound I'm after.
Lynn Olson said:
I noticed that too last night. Very interesting. The GPA softparts are really exceptional in that response even in breakup is really smooth. I haven't seen any other drivers with a cone or surround that looks the GPA stuff. I wonder where they get them from? And the pole vents out through the dustcap. Weird.
augerpro said:
The pole vents through the dustcap as they use a solid piece of steel for the top center pole piece (on top of the Alnico) This was common back in the day, most other drivers like this used a fully screened dustcap. Its either this or no dustcap (like our TD drivers)
augerpro said:
TD15M - also I guess thats the reason I didn't see it
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