A friend of mine recently acquired an Orpheus disc music box, of
disc diameter about 57 cm, with a comb construction we have never
seen before.

There are two combs, mounted as usually left and right of the centre
drive wheel.  The teeth of these combs are plucked by star wheels.
Each comb has 55 teeth.

An absolute surprise for us is a third comb with another 55 teeth,
mounted above the left comb.  The steel of this third comb (body) is
much thinner than normal combs are: only  0.7 mm.  The tips of the
teeth of this third comb are about five millimeters above these of the
lower comb.  No star wheels pluck these teeth.  The two left combs
(one above the other) are screwed with three screws; the right comb
is split into two partitions: one partition is screwed with four screws,
the other one with two screws.

The only explanation which I could imagine is that this third comb acts
as a "Bourdon" comb as do the Bourdon strings on a stringed instrument,
as a Theorbe, for example.  This Bourdon would resonate with the primary
comb with the same and/or a harmonic frequency without being plucked.

Physically this explanation sounds reasonable for me but seems to be
very speculative, because never before I have heard or read about such
a "Bourdon comb".

Does anybody know more about this secret or have a better explanation?

Waiting for clarification,
Christian Greinacher, Germany