[Scott Dorsey]

geoff wrote:
On 17/09/2020 7:11 am, Scott Dorsey wrote:
Roy W. Rising wrote:
When I started in TV sound in '65, I was told the mic preamp input impedanc=
e should be "2K or greater" to avoid loading ribbon mics, which lose HF per=
formance when loaded.

And see, when I started in the seventies, I was told the opposite, that
ribbons wanted to see a lower impedance. Roy is correct, and Olson backs
him up, and what I was told was wrong, but apparently a lot of people
believed it at the time.

Surely all passive ribbon mics have output transformers, and the optimal
loading would be dependent on that, which could be different for every
model or brand ?

The RCA ribbons, and most other ribbons that are copies of the RCA, don't
need any electrical damping. Consequently they work best into an open,
but you don't get any signal that way, so in real life we try for the
highest impedance possible given noise limits.

This may not be the case for highly tensioned ribbons, although it seems
to be the case with the Beyers.

There is a really good discussion of this in Harry Olson's book on acoustics,
which goes through the math and shows a very good electrical model for the
ribbon mike which still has not been improved on after all these years.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."