[ScottW]

"William Sommerwerck" wrote in message
. ..
Impedance match??? Between the vinyl disc and the
platter? Please explain.

There's a goofy idea the platter should be made of the
same stuff as the record, or nearly so.

There's nothing goofy about the idea, any more than connecting a 75-ohm
antenna to a receiver with a 75-ohm input with 72-ohm cable (I don't think
there's any 75-ohm coax) is a goofy idea.

One of the requirements for "good" LP playback is to minimize all "unwanted"
vibrations, either by damping them or avoiding them in the first place.
Phono playback is, after all, mechanical. (Just thinking about it upsets me.
Uck.)

The LP itself is not mechanically "dead". Playing it causes the _both_ the
stylus and the LP to vibrate in an image of the recorded sound. The
vibrations in the LP take a finite amount of time to die away and will
"play" the stylus. This effect is one of the reasons that LP lovers complain
that digital recording is lacking in ambience -- what they're hearing is the
record surface playing the stylus more than once.

There's no way to prevent the LP's surface from being set into motion,
unless you could find an LP material that was infinitely stiff.

Having a bit of experience in testing the vibration transmissibility of
material, I have to say that soft plastics like vinyl are rather poor
transmitters. Vinyl being so compliant will have a rather low cutoff
freq. I've also read that this is to it's benefit in surviving the stress
applied by the stylus and remaining in plastic state allowing
recovery without permanent deformation.

One approach
is to clamp the disk against a soft pad. * Another is to make a platter
whose mechanical impedance is similar to that of vinyl. This impedance match
allows the vibrations to march into the platter, rather than being reflected
back.

* I heard the effectiveness of this about 25 years ago when James Boyk at
Caltech sent a review LP with a severe warp. The side with the warp "up", so
that it could not be pressed against the Platter Matter pad I was using, had
a much different tonal balance (brighter, thinner) from the other side.

I think this issue is better handled by improved cart technology
lowering the eq. mass of the stylus and the force it imparts on
the record than on the other side.

ScottW