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sa660
12-08-2008, 03:31 AM
This is not a speaker related question but since magnet are comon in most JBL Speaker :D.

I am working for a new company MA/COM. They are using magnet and ferrite.
Our biggest problem is to ensure that the ferrite are fully saturated with a uniform field. The pill assembly is with disk place on top of each over?
Any advice to ensure that the magnetic field goes through the full cross section of the ferrite?
Shape, size, fillet, chamfer pole piece ???????
Guido
12-08-2008, 04:22 AM
I can't really help you.

But:
Before every recone I measure the magnetic field in the speaker gap with a teslameter. If I go round the gap I don't measure a constant field.
e.g. round a 2235 gap I measure between 1,2 - 1,35 Tesla.
CauYem
12-08-2008, 04:24 AM
This is not a speaker related question but since magnet are comon in most JBL Speaker :D.

I am working for a new company MA/COM. They are using magnet and ferrite.
Our biggest problem is to ensure that the ferrite are fully saturated with a uniform field. The pill assembly is with disk place on top of each over?
Any advice to ensure that the magnetic field goes through the full cross section of the ferrite?
Shape, size, fillet, chamfer pole piece ???????

I guess you're making RF/Microwave isolator/circulators. Use pole piece the same size of magnet in between magnet & ferrite. Normally, circular shape is the best. W/O uniform field, electrical performance will degrade over temp & IMD will be very high.

Do you use top or side magnets? Which magnet do you use (M8, Alnico or SmCo)?
Jan Daugaard
12-13-2008, 01:09 PM
There are extreme demands on magnet field homogeneity in MRI (Magnetic Resonance Imaging) scanners. This article discusses the problem of achieving a strong homogenous magnet field:
http://en.wikipedia.org/wiki/Magnetic_resonance_imaging#Magnet
It may be worth while studying the construction of MRI scanner magnets.
sa660
12-15-2008, 06:27 AM
CauYem,

Exactly as you say we are using pole piece with identical diameter.
I guess the pole piece will help but I do not beleive it will make a bad magnet much better.

Thanks,