[Arny Krueger]

"William Sommerwerck" wrote in
message


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.)

Counterpoint:

Newton taught us that F=MA, and other than the relativistic adjustment per
Einstein, its still today.

The vibration of a record is caused by the effective mass of the stylus
acting on the mass of the record. A LP playback stylus has an effective
mass of from 0.3 to 1 milligram. A LP record weighs over 100 grams. The
record weighs from 100,000 to 300,000 times as much. The ratio of masses
puts any reactions by the vinyl at least 80-100 dB down.

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.

As is usual with most golden ear myths, its all about quantification. There
is no doubt that the playing a LP causes it to vibrate along with the
musical waveform. It is just that the vibrations are so far below the noise
floor that even though we can hear coherent sounds well below the noise
floor, we still can't hear them.

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. 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.


A typical James Boyk experiment - no reliable evaluation of results and no
quantfication of the effect in terms of its probable audible effects.