When you do the measurements it is often very surprising, as too what turns out
ot be magnetic, and what is ok.
Remember for far field measurements a magnetic field drops of at an inverse
cube rate (approx.).
So being very crude with the equations (as the physics often hurts my head), if
you have a large powerful magnet of say, a 20 cm diameter. At 2.1m the field
strength is already reduced to 1/9000th and at 4.6m to nearly 1/10th of the
max field strength measured at the magnets face.
Ted Rook wrote:
JBL Professional Audio makes heavy duty loudspeaker drivers which feature the
traditional big magnet at the back. These items are airfreighted all over the
world daily. I recall seeing an airfreight label on the cartons which
declared the contents to be 'magnetic'. The figure given in a recent post for
maximum allowance, mG at meters distance, would be exceeded by these devices,
I think. You could try the JBL website, their US headquarters is in Los
Angeles CA, they are part of the Harman Audio group.
Best Regards
Ted Rook, Console Engineering, ext 4659
Please note our new location and phone numbers:
Crest Audio Inc, 16-00 Pollitt Drive
Fair Lawn, NJ 07410 USA
201 475 4600 telephone receptionist, 8.30 - 5 pm EST.
201 475 4659 direct line w/voice mail, 24 hrs.
201 475 4677 fax, 24 hrs.
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