Easy method to test the flux of a alnico driver

[ds23man]

I was just thinking of a easy method to check the flux....

The Fs of a speaker is related to the strenght of the flux field. A simple example: If you put a 2235 recone in a E140 basket, the Fs will shift op to 23Hz. So you can check your driver in a simple way with an impedance plot. If the flux is down, the Fs will go down.

[ivica]

I was just thinking of a easy method to check the flux.... The Fs of a speaker is related to the strength of the flux field. A simple example: If you put a 2235 recone in a E140 basket, the Fs will shift op to 23Hz. So you can check your driver in a simple way with an impedance plot. If the flux is down, the Fs will go down.

Hi ds23man,

Yes, you are right about that the B*L influence in the driver free air impedance,
but (BL) measurements is not so easy as it seems to be. Its influence to the Fs is not so much as can be expected. But if You KNOW Rms (mechanical resistance of the driver suspension foam+spider), then BL can be get easier.

You can read about Fs sensitivity in:
http://en.wikipedia.org/wiki/Thiele/Small

and concerning the BL influence Dr.Keele work:
("Comparison of Nominal Efficiency vs. True Efficiency with High-Bl Drivers")

http://diy-audio.narod.ru/litr/Keele...ff_High_BL.pdf


I think that better way would be if You have one driver as 'reference unit with known BL', and connect to the 'DUT- device under test' "face-to-face" and measure BMF ( Voltage that 'the DUT unit produce, while the reference driver is 'energized buy reference voltage amplitude and frequency'. May be some of our forum member can give us much more information.

Regards
Ivica

[Hoerninger]

ds23man,
what are you looking for, magnetic flux or BxL?
BxL can be measured, which is not too complicated.
____________
Peter

[badman]

The Fs is related to the Qms and cone assembly weight/size/etc, more than anything else. Testing Qes or Qts is a better way, as either will be substantially higher in a demagged alnico driver.