Recently there has been a discussion about alternative materials for
music box bedplates.  This is something that I have been thinking about
myself, so this seems like a good time to introduce myself and throw in
my two cents worth.

My name is Jonathan Herz.  I live in Montpelier, Vermont.  I am a
collector and neophyte restorer of cylinder musical boxes.  My father,
Eric Herz, built harpsichords in Boston for 40 years, so I come by my
interest in antique instruments honestly.

I am a mechanical engineer.  My understanding of the bedplate issue
comes from an engineering materials point of view rather than any great
understanding of the mysteries of acoustics.  What I know for sure:
Stiffness is a separate property from strength.  For two parts of the
same shape and size but different materials, stiffness is proportional
to the elastic modulus (Young's modulus).  Cast iron has a Young's
modulus 50% higher than aluminum, but it is three times as dense.  An
aluminum plate of equal stiffness to a cast iron plate would be 15%
thicker and 60% lighter.

It is not clear to me whether this would be an advantage, however.  The
plucking energy of the tooth is transmitted to the bedplate no matter
what the weight or stiffness of the bedplate (the only losses in the
tooth are air resistance and frictional heating of the tooth).  A
lighter bedplate would vibrate at a larger amplitude, but since it is
lighter, the vibrations would not represent more vibrational energy.
Would it deliver any more energy to the soundboard?  I don't know.  The
resonant frequency of the bedplate would also be increased.  Again, is
that good or bad?

However, there is another issue that I have always wondered about --
cast iron bedplates.  Cast iron has a very large hysteresis curve.  That
means that it is very good at absorbing vibrational energy by turning
it into heat.  This is why machine tools are almost always made of cast
iron.  The iron damps out vibration and reduces tool chatter.  I don't
know if this is a significant factor in music box volume, nor do I know
any easy calculation for estimating the hysteresis losses.

It would be interesting to know if any cylinder box collectors have
observed a general difference in performance between movements with
brass and cast iron bedplates.  Also, I understand that some reproduc-
tions of the Regina were made in the 1970s with aluminum bedplates.
Can any observations be made from these?

Regards,

Jonathan Herz

 [ Welcome to MMD, Jonathan, and thanks for the engineer's view.
 [ At least one comparative test should be made: compare the sound
 [ of the different plate materials without the wooden box.  If all
 [ else is equal then you can estimate the comparative losses.  (Use
 [ a microphone and amplifier if you can't hear it. ;)  My guess is
 [ that the bedplate losses are insignificant when compared to the
 [ energy dissipated in the wood (as heat) and the useful energy
 [ of the audible sound.  -- Robbie