In article , Don Pearce
wrote:
On Tue, 29 Sep 2009 16:35:45 +0100, Jim Lesurf
wrote:


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.

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.

Can't really say, but possibly. IIUC it is fairly usual for the compliance
at audio to be quite different to the LF/static value. Various reasons.

e.g. If the suspension is a block of 'rubber' (or similar) then the
effective pivot point may alter with frequency as well as the level of
mechanical resistance and restoring force vary with velocity or
accelleration.

Think of the superball and 'potty putty'. Materials whose properties aren't
simply linear elastic.

IIRC one of the things Shure did was to put a small mass onto the
cantilever connected via a rubbery link. At LF this just moved with the
cantilever as an added mass. But at HF the mass stayed were it was, and the
cantilever had to compress the material as part of the suspension losses,
etc.

However the problem is that figures are often quoted as being 'effective'.
So a like quoting a modulus of impedance like 'X Ohms' at an unstated
freuency rather than saying 'Z farads'. if you look back as far as Walton
you can see he/she was focussed on mechanical (complex) impedance which is
more revealing, but can be a devil to measure!

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html