[CAUT] "D" with a ghost

[James Ellis]

Another brand new D has arrived in Knoxville, TN.  Some of us in the
Knoxville Chapter were checking it out at the dealer's prior to our regular
meeting last night.  I noticed a very prominent ghost-after-sound at note
C#-6.  None of the other treble notes were doing this - just the C#-6.
What first called my attention to the C#-6 was its apparent short
persistence, but then I noticed the ghost sound when I released the key.
The ghost was persistent as well as pronounced, like a wide-open string
somewhere, but no dampers were hanging up, and none were seating poorly.

We even checked to see it the sound was coming from another piano (an open
B that was sitting side-by-side with the D), but it was not.  The whole
body of the D just seemed to resonate with that sound.  So, what was it?

It turned out to be the rear duplex of note C-4, whose fundamental was
exactly on pitch with the fundamental of note C#-6.  The muting braid
stopped a few unisons below that point in the scale.  The remedy was
obvious, but I suggested we just wait and see if anyone else notices this
before anyone fixes it.

There is a good chance that the ghost will come and go as the relative
humidity changes and the soundboard shifts, because that section of the
duplex will be very sensitive to it - more so than the speaking lengths of
the strings.

This is proof of what I have said so many times.  The vibrations of
individual speaking lengths do not couple across the bridge to their
individual duplexes.  They can't.  Instead, the vibrations couple all up
and down whole sections of the bridge, to duplexes and speaking lengths alike.

Jim Ellis