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Old 26th June 2009, 10:00 AM   #21
thadman is offline thadman  United States
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Thanks for the massive contribution of data to the loudspeaker community, it is a huge resource! Simply stated, YOU are the MAN!
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Old 28th June 2009, 03:16 AM   #22
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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%2...nt_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.
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Old 28th June 2009, 03:53 AM   #23
ScottG is offline ScottG  United States
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Hi Brandon.

Was the 18Sound driver's THD measured with AIC on?
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Old 28th June 2009, 04:21 AM   #24
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Yep AIC on.
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Old 28th June 2009, 08:21 PM   #25
JoshK is offline JoshK  Canada
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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).
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Old 28th June 2009, 09:14 PM   #26
ScottG is offline ScottG  United States
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Quote:
Originally posted by augerpro
Yep AIC on.
Graci!
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Old 28th June 2009, 09:31 PM   #27
ScottG is offline ScottG  United States
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Quote:
Originally posted by JoshK
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).
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.
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Old 28th June 2009, 09:35 PM   #28
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Quote:
Originally posted by JoshK
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).
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.
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Old 28th June 2009, 09:43 PM   #29
ScottG is offline ScottG  United States
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Quote:
Originally posted by augerpro

I guess JohnJ jsut needs to get around to putting an alnico motor on the TD12M.
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.
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Old 28th June 2009, 11:41 PM   #30
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Yeah maybe...the one nice thing is the TD drivers really can do bass. I would imagine most speakers using these drivers are fullrange, with no sub. With the other pro drivers they bass is just adequate if you are lucky. So it's good trade for most people I would guess.
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