"GregS" wrote in message
...
In article , "David Grant"
wrote:
My understanding (of the sales pitch/marketing ?) of the function of
cones
or spikes was that they were supposed to act as a 'physical diode'..in
other words to allow unwanted vibrations and micro-motion to transfer
from
the speaker cabinet into the thick end of the cone and then down through
its point to a massy, inert body below it (floor, shelf, concrete slab
etc) which would then absorb the vibes and in theory refuse to allow
them
to be reflected back up the spike/cone again ? I don't know how
complete
this diode principle was meant to be, in terms of allowing one way
transmission of kinetic energy only ? Wouldn't that depend on a
gradation
of absorptive materials on the downwards path so that 'reflections' of
energy wouldn't travel back up the cone again ...? So if the cone point
terminated in a full sandbox, for example, that would presumably act as
an
energy-sink. Dunno, that's my shaky (ha !) understanding of the "theory"
anyway.
RT
I studied transmission lines from an electrical engineering standpoint a
few
years ago and I expect this represents the mechanical equivalent. It
should
be possible to minimize vibration reflections at the termination via
impedance matching (where impedance in this case is a complex value based
on
mass, spring, damping).
The diode analogy sounds iffy. The direction of elecron flow can be
controlled using charges but a vibration carries no polarity. I don't
believe an atom of matter has any means with which to determine whether a
vibration came from direction x or direction -x. It would have to
communicate with adjacent members to determine the direction of
propogation,
and then somehow it would have to absorb that energy or transmit it
depending on the case. That doesn't sound like a natural property of
matter.
I suspect someone looked at the spikes one day and made a conclusion
for no good reason. The spikes does go through carpeting and touch the
floor, which
for no other reason keep the speaker from rocking back and forth on the
rug.
I think I have also seen spikes which look more like nails. I would rather
have the speaker on the rug, but the spikes look pretty both on the rug
and
on a wooden floor, except when you try to slide them.
greg
You are obviously far too pragmatic and sensible about resonance physics, so
let me provoke a little controversy by introducing you to the black arts of
Shun Mook, which have been around for many years now. Now let's see...these
should stir the pot sufficiently, at least for the entree course ;-)
http://www.shunmook.com/text1.htm
http://www.shunmook.com/text2.htm and for comprehensive overview
http://www.stereophile.com/features/69/ (10+ pages of followup and
reader's replies too !)
Ray