BL^2/Re Value Doesn't Seem Right in FEMM - diyAudio
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Old 22nd August 2013, 05:09 AM   #1
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Join Date: Jan 2013
Default BL^2/Re Value Doesn't Seem Right in FEMM

Hello,

I've been messing around in FEMM but the BL^2/Re value I'm getting seems to be too high. I was hoping someone who has a lot of experience with FEMM could verify if my figures seem correct.


Here are the specs for Subwoofer_C

Coil
ID: 75.95mm
OD: 82.55mm
WW: 65mm
Wire Diam: 19 AWG (0.912mm)
Re: 3.71 ohms (Dual 1.85 ohms in series)
BL: 34.49
BL^2/Re: 320.64

Magnet:
OD: 180mm
ID: 95mm
TH: 20mm

Top Plate:
OD: 180mm
ID: 91mm
TH: 10mm

Bottom Plate:
ID: 40mm
OD: 180mm
TH: 10mm/23mm

Pole Piece:
OD: 73mm
ID: 40mm
HT: 105mm



Here are the specs for Subwoofer_B


Coil
ID: 75mm
OD: 84.6mm
WW: 65mm
Wire Diam: 17 AWG (1.15mm)
Xmax: 27mm 70% BL
Re: 0.938 ohms (single 0.938 ohm)
BL: 14.1
BL^2/Re: 240

Magnet:
OD: 180mm
ID: 95mm
TH: 20mm

Top Plate:
OD: 180mm
ID: 87.6mm
TH: 10mm

Bottom Plate:
ID: 40mm
OD: 180mm
TH: 10mm/23mm

Pole Piece:
OD: 73mm
ID: 40mm
HT: 105mm



You can see the FEMM graphs in the attached photos. The motor is not that big but as you can see the BL^2/Re figure is quite large for both of them.
Attached Images
File Type: png subwoofer_c.png (83.0 KB, 28 views)
File Type: png subwoofer_b.png (97.1 KB, 27 views)
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Old 25th August 2013, 07:25 PM   #2
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Join Date: Jan 2013
Here's a pic of the specifications I have set for the 17 AWG Copper wire.

Click the image to open in full size.
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