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Old 13th August 2012, 05:20 AM   #1611
NEO Dan is offline NEO Dan  United States
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Default After seeing the 10mm top plate 11mm x-max is within the realm of possibility...

Not to take a poo on the Ande...
I can't find complete specs for these drivers but what I see for the Ande, the 10mm top plate is thick and so I'd venture a guess that the coil is ~17mm long... (17/2)+(10/4) would put it in the 11mm ballpark. Having no idea about the JB1500N, the straight overhung number guess is 18mm coil and 6mm gap plate as it looks pretty thin. X-max is a numbers game and both woofers are probably Chinese in origin so short of measuring them yourself you are flying blind. The Ande is stronger on paper and due to the thick top plate it also sports ~1.5mm more x-max as a calculated guess. How long the coils actually are is hard to know without tearing a driver apart...
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Last edited by NEO Dan; 13th August 2012 at 05:22 AM.
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Old 13th August 2012, 05:23 AM   #1612
Djim is offline Djim  Netherlands
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Hi Dan,

Both are complete different drivers from different Chinese plants.

Ande

Fs Sound
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Old 13th August 2012, 05:27 AM   #1613
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just thought id bring the pic from last page forward

Click the image to open in full size.

edit:

theyre definately different.

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Old 13th August 2012, 05:44 AM   #1614
NEO Dan is offline NEO Dan  United States
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The JB1500N Sd 908cm² seems a bit inflated... that's 340mm∅, the cutout is 355mm∅
The calculated Sd for the JB1500N is 878.261201056914cm²... still looking a bit fake...
BL²/Re=73.4563636363636... /Sd=83.6384023754706

The Ande driver calculates to be 841cm², more realistic...
BL²/Re=83.2654545454546... /Sd=99.0076748459627

The Ande is stronger but I don't think x-max is almost double...
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Last edited by NEO Dan; 13th August 2012 at 05:49 AM.
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Old 13th August 2012, 05:59 AM   #1615
NEO Dan is offline NEO Dan  United States
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Proof that I should not be posting at 2AM... this is flawed
Quote:
Originally Posted by NEO Dan View Post
the 10mm top plate is thick and so I'd venture a guess that the coil is ~17mm long... (17/2)+(10/4) would put it in the 11mm ballpark.
Time to go to bed
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Old 13th August 2012, 09:50 AM   #1616
djk is offline djk
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"the 10mm top plate is thick and so I'd venture a guess that the coil is ~17mm long... (17/2)+(10/4) would put it in the 11mm ballpark."

A 17mm coil would have 7mm overhang, so (7/2)+(10/4)=6mm x-max.

The JBL 2226H has a 19.05mm coil, 8.1mm top plate, so (10.95/2)+(8.1/4)=7.5mm (JBL says 7.6mm).
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Last edited by djk; 13th August 2012 at 09:58 AM.
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Old 13th August 2012, 10:42 AM   #1617
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by NEO Dan View Post
..............................the 10mm top plate is thick and so I'd venture a guess that the coil is ~17mm long... (17/2)+(10/4) would put it in the 11mm ballpark..................
What are you calculating?
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Old 13th August 2012, 10:44 AM   #1618
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by djk View Post
..........A 17mm coil would have 7mm overhang, so (7/2)+(10/4)=6mm x-max.

The JBL 2226H has a 19.05mm coil, 8.1mm top plate, so (10.95/2)+(8.1/4)=7.5mm (JBL says 7.6mm).
why the plate/4 correction?

What is that correction and why is it applied?
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Old 13th August 2012, 11:17 AM   #1619
djk is offline djk
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The thought is that it represents the 70% Bl point with only 75% of the gap filled with coil.

The old standard was coil overhang/2 plus 10% of the total coil length, but this did not predict the 10% distortion point (especially with the newer thicker top plates) and required a current probe and an oscilloscope to observe the distortion in the current waveform (and some guessing as to what constituted 10% distortion).

Most of the pro sound speaker manufacturers are following the gap height/4 method, so it is usually and apples vs apples comparison.

Faital Pro chooses not to follow, and uses to use Xmax = [(winding depth - magnetic gap depth) / 2] + (magnetic gap depth / 3) , which tends to make their specs look better (that what they probably are).

The gap height/4 method correlates well with Du-Max measurements for 70% Bl.

An Aura/TC Sounds 18 has an underhung 3" gap with a 1.5" coil, they claim a geometric x-max of 19mm and a 70% Bl of 31mm (30% of the coil out of the gap). Mechanical noise on the back side of the driver starts to climb above about 1.5" P-P travel.
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Last edited by djk; 13th August 2012 at 11:33 AM.
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Old 13th August 2012, 11:38 AM   #1620
AndrewT is offline AndrewT  Scotland
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Take a 17mm Voice Coil and inseret it into the 10mm tall gap across the poles.
The Xmax used to be stated as [17 - 10] / 2 = 3.5mm
You are saying that by accepting a much lower BL and the distortion that ensues from the lower BL that Xmax is now "longer".
eg.
low BL version of Xmax = [17 - 10] / 2 + 10/4 = 6mm
or very low BL version of Xmax = [17 - 10] /2 + 10/3 = 6.83mm

Balderdash !!!
Xmax is the linear excursion where the Voice Coil is still inside the major part of the gap flux. Yes there are fringes at the edges of the gap where the flux is almost as high as within the gap. So the 3.5mm result will be an underestimate of the measurable Xmax.

Xmax cannot be increased by >70% (6 cf.3.5) or by >95% (6.83 cf 3.5) just because the manufacturers/retailers want to exaggerate the performance of their product.
Lies and damn lies seems little different from disreputable manufacturers' claims when it comes to audio product.
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