Noisy 'D' strings

[Paul S. Larudee]

Lew Jones wrote:
> 
> A four year old Steinway 'D', on stage at an area University has a
> situation on which we invite comments.
> Note 21, F (1st steel string unison on the treble bridge), sounds as if
> the tone is being modulated at a certain frequency (about 12 Hz).  The
> three strings of the unison sound very nearly alike.  The unison is
> tuneable but at best has a slight beat (vibrato or tremolo).  It sounds
> as if this unwanted frequency is being generated by a fan or some such
> in the air moving equipment, but this is not the case.
> A 25 year old 'D' on the same stage has not displayed this same
> condition,
> 
> Lew Jones and Joe Brown
> lewjone@prodigy.net

Hi Lew & Joe,

These are the puzzles that make our job interesting.  If the tremolo is
roughly equal on all three strings individually, it is unlikely to
originate in such things as bearing deficiencies or string anomalies
(e.g. torque, deformation, etc.).  In fact, it is unlikely to have
anything to do with the primary sound generators of the note.

It is more likely that the frequencies produced by the primary
generators are either inducing a sympathetic vibration or resonance, or
are interacting with another source of vibration.  One way to test for
this would be to tune the note to a different frequency and see if that
makes a difference.  Obviously you can't leave it there, but at least it
would confirm or deny the hypothesis.

You have obviously already considered at least some external factors
such as a fan, but other oscillating equipment can be really insidious. 
Computers and other AV equipment have fans, and perhaps the acoustic
characteristics of a particular location on the stage might also play a
part.  Have you tried moving the pianos around?  Might the other D
induce the sound in the same position?  Might the problem D fail to
produce the sound if moved to a different location?

Lastly, of course, perhaps the sympathetic vibration or resonance is a
part of the instrument itself.  Try putting the two Ds right next to
each other, alternately in back-to-back and facing position, and then
play the note on the older D, making sure that it is tuned to precisely
the same frequency as on the newer one.  Does it induce the beats in the
new one?  Also try thoroughly muting out everything possible except the
note itself, including not only the speaking lengths, but all the front
and back lengths as well, and even the non-speaking lengths of the
note.  Then unmute a little at a time to see when the sound returns.

If none of this yields any clue, then to paraphrase Sherlock Holmes, the
remaining possibility, however improbable, must be the truth.  In this
case, the only thing I can think of is an anomalous resonance in the
transducing elements of the piano, such as the bridge, soundboard and
case.  I hope that's not it.

Good luck, and please share what you fid out (or don't).

Paul S. Larudee, RPT
Richmond, CA