multiple unison strings

[Michael Wathen 556-9565]

>Subject: Re: multiple unison strings


On the subject of multiple unison strings I was very surprised to
learn that the Weinrich phenomenon is also observed in harpsichords
under certain conditions. I've appended a very interesting message
on this subject from John Sankey.

Stephen Birkett
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
REPLY:
      This stands to reason because of the way a harpsichord is c
constructed.  In the normal configuration there are two eight foot
choirs that when coupled together will play a two string unison.
These unisons can be thought of as essentially having the same
length, however, they are plucked in different places on the
string.  These ensures that their phase differences will not be equal
because one wave will be reflected at the termination at a different
time than the other.  This is analogous to the problem in the piano
where the hammer does not strike all three strings at the same time.
It produces a distinctive timbre which is impossible to straighten out
with tuning and is highly undesirable in the piano.

I intend to say more about Mr. Weinreich's work latter.  But I will
leave you with a quote from his paper as it first appeared in <The
Journal of the Acoustical Society of America>, Vol. 62, No.6, December
1977, p. 1482.

      It appears that the fine tuning of the unisons is not
      so much a matter of regulating the beat rate as of re-
      gulating the amount of aftersound. We saw in Fig. 5
      how the amount of aftersound can depend on the degree of
      mistuning, being affected strongly by a change of even
      1 cent in the frequency of a string.  Clearly, the after-
      sound will also be affected by irregularities of the
      hammer, which cause one string to be hit harder than
      another, which may cause a greater or lesser excitation
      on the horizontal vibration. It is our conjecture that
      an excellent tuner adjusts the      unisons so as to compensate
      for hammer irregularities, making the total aftersound
      uniform from note to note; this gives the piano the
      characteristic "singing" quality that less talented
      techicians are unable to produce.


Michael Wathen