On Tue, 29 Sep 2009 16:35:45 +0100, Jim Lesurf
wrote:

In article , Don Pearce
wrote:
On Tue, 29 Sep 2009 09:19:41 +0100, Jim Lesurf
wrote:


The presumption seems to be that when you see an HF resonance with a MM
it must be purely 'electronic' in nature. This isn't really the case.
When experimenting with electronic loading you may simply be trying to
trade off two quite different HF LP resonances - one electronic and the
other mechanical - to get an overall optimum. But so far as I know,
this has largely been ignored in recent decades. Preumably because of
the (incorrect) assumption that MC designs are immune.


How does the HF damping thing work? It seems to me that if you can
dissipate energy quickly enough for critical damping at HF, it will be
almost solid at the main LF resonance

One aspect of it - as explained in some ancient JAES papers by the people
at Shure - was to use suspensions whose effective 'resistance' increased
with frequency. Also to have a distributed arrangement for the suspension
so that some parts had more effect at HF than at LF. IIRC one of the
properties of 'rubber' materials is that the mechanical loss tends to
increase with frequency.

Another aspect is to have a material whose internal loss varies with
velocity or accelleration.

Note also that the cantilever resonance may not simply be the simple of the
displacement. It can be that the cantilever bends or flexes in the same
direction either side of the suspension. So that would affect the
suspension differently.

Slainte,

Jim

Ok, that's interesting. Also interesting is the fact that A/T give two
compliance values for the OC9, static (35mm/N) and dynamic (9mm/N). I
wonder if this is to reflect the frequency dependence of damping. On
my 3009II the primary resonance comes in at 12Hz, which puts the
compliance in the same kind of region as the V15.

d
--
Pearce Consulting
http://www.pearce.uk.com