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Old 7th February 2013, 05:59 AM   #21
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Please note when exporting flux data from FEMM, the (Normal flux density) curve must be used:

Click the image to open in full size.

The exerted force felt by the coil depends on the direction (or angle) of the flux. This is the flux that is perpendicular to the coil. The straight is the tangential.
So, sqrt(perp^2 + tang^2) = magn of flux density and, angle = atan2(perp,tang)

Here is a short proof:
in the 1st image below the coil is put in a field where the angle is not perpendicular, therefore BL is just 0.22, in opposed to the 2nd image where the angle is more perpendicular, now BL is ~4.0. The next images show the directions when only the magnet/coil is enabled, respectively.

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.


(this is how the force roughly looks like: )

Click the image to open in full size.


Next time i will share the application and the details, how to use it etc..
Attached Images
File Type: png 3_femm.png (13.4 KB, 78 views)
File Type: png 3_flux1.png (38.2 KB, 76 views)
File Type: png 3_flux2.png (31.3 KB, 77 views)
File Type: png 3_flux3_magnetonly.png (6.5 KB, 76 views)
File Type: png 3_flux4_coilonly.png (5.1 KB, 76 views)
File Type: png 3_flux6.png (14.1 KB, 77 views)
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Old 7th February 2013, 07:04 PM   #22
NEO Dan is offline NEO Dan  United States
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Nice work.

DDD coil:
Click the image to open in full size.
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Old 7th February 2013, 08:26 PM   #23
OscarS is offline OscarS  United States
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Quote:
Originally Posted by NEO Dan View Post
Nice work.

DDD coil:
Click the image to open in full size.

Yup. That's it alright. Been a while Since I fixed up that WGTi.

One thing I saw with that simulation of the DDD motor, is that the coils appear to be centered on each magnetic gap, where as in reality they are offset towards each other so that only the last 0.5" of each coil are within the physical measurement of each 0.5" gap. That's how it is for the mobile audio subwoofers anyhow.

Last edited by OscarS; 7th February 2013 at 08:29 PM.
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Old 7th February 2013, 08:26 PM   #24
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W12GTi?
W12GTi MkII | A patented, cast-frame 12" (300mm) DVC subwoofer with 4000W peak power handling | JBL US

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Akos
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Old 7th February 2013, 08:45 PM   #25
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Hi OscarS,

It's good to see someone who does reconing on subs.
There was a time when i was interested in getting bad/misadventurous subs and fix them. It's worth to do that. At least for their NEO structures.

Do you mean this way: ?

Click the image to open in full size.

Click the image to open in full size.

According to the simulations, the BL curve is not better. But i'm going to give it a try in FEMM, and see the real results of the evaluations.

Regards,
Akos
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File Type: png 4_jbl1.png (46.8 KB, 71 views)
File Type: png 4_jbl2.png (47.8 KB, 70 views)
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Old 7th February 2013, 09:01 PM   #26
OscarS is offline OscarS  United States
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The issue I see with your model is that you don't have enough space between your magnetic gaps. Notice how there is 0.53" in between the 1.4" long coils on the former. With this spacing it allows the coils to be "inner hung" without having any windings outside of the magnetic caps. Here is what I'm talking about:

Click the image to open in full size.


So to correctly model the W12 and W15 GTi subwoofers, you need to have the 0.5" long magnetic gaps 2.33" apart (on the inside). This places the gaps at the outermost end of each coil's last 0.5" worth of windings.
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Old 7th February 2013, 09:48 PM   #27
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Wonderful. Absolutely wonderful.

Anybody read the book by the London student who tried to build a toaster from scratch (yes from copper ore, etc.)? Kind of a mess but a fun book.

I have often wondered about a Darwinian dead-end: "dynamic" magnets. Today, easy to make large, clean DC to power the magnet. Could these be more powerful or otherwise better than permanent magnets? (I won't even joke about the value of super-conducting magnets like in MRI and other applications.)

FWIW, when you are winding coils, you can create great motional feedback opportunities. THAT is the way to address distortion, not trivial improvements in pole piece geometry.

Ben
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Old 8th February 2013, 12:32 AM   #28
NEO Dan is offline NEO Dan  United States
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Wow.
You guys should take your attitude somewhere else.

Akos,
I think you've done some great work, but I wouldn't go out of your way to provide anything, it would appear to be a waste of your efforts.
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Old 8th February 2013, 02:34 AM   #29
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I believe there is currently some agreement that a forum with a light-handed Moderator can successfully control the crazies and nasties.

B.
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Old 8th February 2013, 03:58 AM   #30
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Thanks Dan,

OscarS, the application gives the same results as FEMM.

"FWIW, when you are winding coils, you can create great motional feedback opportunities. THAT is the way to address distortion, not trivial improvements in pole piece geometry."

I've heard that they're going to use HgBa2 for their new motor structures. It doesn't require as low temperature as the previous ones.

Why Modern subs have 2nd & 3rd harmonics of level around -30dB then? I assume they are well addressed.


The fun thing is that you can find those curves that were evaluated in JBL papers too. Sure they should have been moderated too. And of course they were crazy, and nasty just because they had been searched for the cure.
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