Driver modeling & design. Pole higher than backplate?

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sellurstuff

Member
Joined 2022
#1
Hi,

I'm currently working on modelling an 18inch sub driver from scratch. I have guideline T&S parameters I'm aiming for but they're flexible as the design process continues.

Currently using FEMM to analyse magnetic flux for the magnet coil system. Flux density diagram can be seen below. As well as corresponding Bl(x) curve.
increased pole height new.PNG



1649862454744.png


My main question is. Is it okay to have the pole higher than the backplate like i have here? This is to correctly for symmetry in the BL(x) curve, if it's at the same height then the forward and backwards displacement gives differing BL. I don't see why it wouldn't be okay but all the models I've seen have the pole at the same height as the backplate.

The coil is hard to pic out in the image but it's overhung, 28cm winding depth.
 
#2
sellurstuff said:
Is it okay to have the pole higher than the backplate like i have here?
Click to expand...
Yes.
sellurstuff said:
This is to correctly for symmetry in the BL(x) curve, if it's at the same height then the forward and backwards displacement gives differing BL.
Click to expand...
BL asymmetry can be used to compensate for suspension asymmetry.
sellurstuff said:
I don't see why it wouldn't be okay but all the models I've seen have the pole at the same height as the backplate. The coil is hard to pic out in the image but it's overhung, 28cm winding depth.
Click to expand...
Most of the models are probably based on what is easiest to stamp or drill out of slabs of iron and ceramic magnets.
FEMM allows you to model any design, regardless of it's difficulty to machine.
Gap Symmetry.png

P.S.
28cm winding depth- 280mm, that would be some long excursion 😉 ...
 
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