[Milsurplus] X-Ray Damage.. more

[J Forster]

These are CRYSTAL MICROPHONE elements. The use a grown piezoelectric
crystal, like Rochelle salt.

They are NOT quartz. They are NOT ceramics.  They DO NOT require
polarizing. If you heat them up the crystals crumble as they are grown
from a saturated water solution and if you heat them the water evaporates.
Curie temperature is irrelevant as they are NOT the electric field
equivalent of permanent magnets.

Look at:

http://en.wikipedia.org/wiki/Microphone

Section 3.4

>From the pic, they were NOT heated and NOT smashed. They were electrically
zapped.

-John



Bob Camp wrote:

> Hi
>
> If the element is a PZT material, it needs to be polarized (polled)
> before it will work correctly. Oddly enough the ceramic pucks in a 455
> Kc filter work the same way. I still can't see how you could do it
> after you get out of the bulk state with normal materials. Normally
> you have to take the stuff above the Curie temperature to make the
> process "stick".
>
> Bob
>
> On Oct 27, 2007, at 12:07 AM, J Forster wrote:
>
> > Bob Camp wrote:
> >
> >> Hi
> >>
> >> I must have missed the first post in the thread. The fact that they
> >> are microphones was something I missed.
> >
> > Yup. The thread started with a post about known good, commercial
> > (Sure)
> > crystal mikes that tested good being zapped during shipment.
> >
> >> A lot of microphone elements are parabolic in their force to
> >> electricity characteristic. At "zero" they do not produce a useful
> >> response. To make them work you "polarize" the element with a high
> >> voltage. It's  a one time process, and normally heat is also
> >> involved.
> >> Sounds like yours got a bit to much ....
> >
> > Crystal mikes are NOT electret mikes. The crystal is cut with a wet
> > string
> > saw from a crystal. There is no 'polarization' process and certainly
> > not
> > during shipment.
> >
> > Best,
> > -John
> >
> >>
> >>
> >> I'm a little surprised that they do the polarization after mount
> >> though. I alway assumed they did it to the bulk material .....
> >>
> >> Bob
> >
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