Flux modulation

[KSTR]

Originally Posted by DBMandrake

I have been wanting to get a pair of broadband attenuation ear plugs as you describe, both for quick high SPL "stress testing" of speakers, but also for going to the movies!

Simon, try those custom fit ones, IHMO the best and really worth the money (I'm using the 25dB variant). The simpler and cheaper universal fit models (from various makers) are OK, too, for a starting point, but I found my right ear canal to have a non-standard shape so those never gave a tight and comfortable fit.

I wish I had been using good plugs earlier in my life when I started to play in rock bands, to avoid the non-recoverable damages in the upper midrange that I have to live with now.

Funny thing, since I started to use these pro plugs I also go to the movies more often, like you I usually can't stand the SPL levels that seem to be common today.

[454Casull]

Originally Posted by speaker dave

Why wouldn't it? Hysteresis just means there is a different curve "going up" than "going down". The graphs you normally see start at the center and swing through a broad region from saturation to saturation (hyst 1 attached) but you can swing H any amount and the characteristics will always swing aroung a minor hysteresis loop. (Hyst 2 and hyst 3).

For those that haven't seen these curves before these are the basic curves of a magnetic material. H is the magnetizing force that you apply, B is the magnetizing flux that remains. The curves flatten top and bottom as a form of saturation. You can apply more H but B won't go any higher. Hysteresis means that the B drags behind as you reverse direction of H, and that is a good thing: without it a magnet woudn't be a magnet. The B point on the return where H is 0 (where the central y axis intersects the curve top middle) shows the remnance after saturation (magnetization).

This also shows how it is hard to demagnetize something. Letting H go to zero leaves the material magnetized (B non 0). You could swing H to some particular negative value, but it is hard to predict precisely what value would be required. In the end, swinging it back and forth in ever diminishing amounts will have it loop around the 4 quadrants (in a minor hystersis loop) until it converges on 0 for B, i.e. demagnetized.

David S.

If I am understanding the graph shown here correctly:

FINEMET MAGAMP

For all drive fields varying between 25 and 75 A/m, the field strength would not change from 1.2 T. Is this correct?