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Yet another DIY AMT
Yet another DIY AMT
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Old 31st July 2015, 01:53 PM   #501
solhaga is offline solhaga  Sweden
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Join Date: Jun 2009
Location: Värsta Götaland
Back to the usual, ideal solid pole pieces, view:
Click the image to open in full size.

I've put in a ledge to which the membrane now easily can be attached to.
The ledge has an angle to get a initial throat exansion.
Also, the foam actually continues upwards, that is backwards in reality, between the back pole pieces.

Simulation:
Click the image to open in full size.

Flow density at the rim:
Click the image to open in full size. Click the image to open in full size.
and in the middle:
Click the image to open in full size.

Looking really good!

Well, back to the shop to cut 32 pieces of 15x2 mm iron rods 145 mm long and sand them in the middle where the edge meets the membrane.
And get some ledges mounted...
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Old 31st July 2015, 02:38 PM   #502
WrineX is offline WrineX  Netherlands
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Looking forward !! To bad my Cnc can't handle steel , would not mind helping you out!
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Old 31st July 2015, 10:43 PM   #503
solhaga is offline solhaga  Sweden
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Thought for a while to also have the front pole pieces backs being slanted, but the first front wave reflection should go straight back; not being deflected and thus mixed with with the adjacent first front waves:
Click the image to open in full size.

Altough the simulations did show a 5 % increase in the magnetic flux density:
Click the image to open in full size.
it is no longer linear across the membranes area:
Click the image to open in full size.

So that suggestion just got documented and forgotten...

Added some material tags (foam, membrane) for the different areas in the inverted motor as well just for clarification. The simulation doesn't change.
Click the image to open in full size.
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Old 1st August 2015, 07:37 AM   #504
båndsei is offline båndsei  Denmark
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Coud you double the amount of 2mm steel bars to get more linariety.

Bernt
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Old 1st August 2015, 08:06 AM   #505
solhaga is offline solhaga  Sweden
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Quote:
Originally Posted by båndsei View Post
Coud you double the amount of 2mm steel bars to get more linariety.

Bernt
Yes, of course.
But then the reduction of the reflection of the back wave will be less.
Also, there´s still variations for the part of the membrane at the front pole pieces.

FEMM:
Click the image to open in full size.

Flux density at back pole pieces:
Click the image to open in full size.

Click the image to open in full size.

Flux density at front pole pieces:
Click the image to open in full size.

Click the image to open in full size.


Anyway, since the motor now is "open" at the back and the back pole pieces are only held in place by the magnets, everything is up for grabs when it comes to back pole pieces configuration.
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Old 8th August 2015, 07:34 AM   #506
onni is offline onni  Sweden
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I had a crazy idea: what if you made the pole pieces out of open cell iron foam? Something like this:
Click the image to open in full size.

Wouldn't that reduce reflections and make the magnetic field more even?

/Anton
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Old 8th August 2015, 09:18 AM   #507
solhaga is offline solhaga  Sweden
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Could be worth a try.
Do you know where to get it?
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Old 9th August 2015, 09:48 PM   #508
esl 63 is offline esl 63  Sweden
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During simulation and design, you could neglect the 2nd harmonic and focus mor on the odd ones. The ear itself generates up to 10% 2nd harmonic so you cant really hear difference between 1% or 2% 2nd harmonic distortion.
So if it helps you with the design of magnet motor, focus less on the second and more on the third.
When it comes to the sharpening of the pole piece try something "lagom" and not so extremely sharp.

https://lh3.googleusercontent.com/-X...yckeprofil.jpg
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Old 10th August 2015, 12:25 AM   #509
solhaga is offline solhaga  Sweden
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Join Date: Jun 2009
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Quote:
Originally Posted by esl 63 View Post
During simulation and design, you could neglect the 2nd harmonic and focus mor on the odd ones. The ear itself generates up to 10% 2nd harmonic so you cant really hear difference between 1% or 2% 2nd harmonic distortion.
So if it helps you with the design of magnet motor, focus less on the second and more on the third.
Yes, of course.

Quote:
Originally Posted by esl 63 View Post
When it comes to the sharpening of the pole piece try something "lagom" and not so extremely sharp.

Click the image to open in full size.
If the bottom is towards the membrane, that bevel is feasible and will probably be what I'll do. It will be much harder to accomplish slant at the top.
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Old 10th August 2015, 10:14 PM   #510
esl 63 is offline esl 63  Sweden
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http://projekter.aau.dk/projekter/fi...061_Thesis.pdf

Look on page 18...
Several studies has shown that 2nd harmonic is not critical.

I can give an example tried myself.
Using Dipole bass with double transducers on each channel, the first clever thought would be to mount them at opposite directions to cancel distortion right? Well it´s "only" the secon harmonic that is cancelled, higher orders is uneffected. The percieved sound is way better if both transducers is working in same direction. The 2nd harmonic seems to have a masking effect on those with higher order.

I live more "värst" than you in "värsta Götaland" btw
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