Hi All,  I purchased my third reproducing piano, a 1913 Artrio-Angelus
upright, in the early 1970s.  The player piano tech who sold it to me
had replaced the long leather first-stage-reduction drive belt with
a plastic orange belt.  This belt was not only so bright as to be out
of place it also hummed a tune and had a large amplitude vibration.
Much of the problem, I think, was due to the elasticity or low spring
constant of the belting material.

I was a research engineer and proceeded to look for a better solution
to the drive belt problem.  I purchased, from The Gates Rubber Comp.,
Vulco-Flex V-belting designated as 40-VO.  This is continuous
V-belting that has a groove in the bottom of the belting.

The belting is cut to length, holes are punched in each end, and the
steel "C" link not only connects the two ends together but the bottom
of the link is protected from causing a tick as it does not extend
below the groove in the bottom of the belt and the belt does not sing
due to it's high spring constant increasing the natural frequency above
the operating range of excitation.

At the time I had to buy 100 feet of this belting to get the 6 to 8
feet I needed.  The excess belting still seems to be flexible after
30 plus years.  The belting at that time was, as I recall, one or two
dollars per foot and may be more expensive now if it is available.
I still have about 70 to 80 feet of this belting.

Allen Ford