Hi All, Preface: With regards to the internal workings of a player
piano, just seeing that something 'does' work by no means helps explain
'why' it works. Also, please know that the purpose of this posting
is not to be critical of the idea of building a Plexiglas model of
a player action; anything that stimulates the human mind to a positive
action is worthwhile.
In my opinion, it would have to be big, and you only need to show one
note. But what would be even more important is showing exactly how
the air flows through the various parts. This could be done by gluing
flexible 'hairs' in and around the various internal components.
However, that still doesn't help explain 'why' it works.
While everything happens very fast, the repeated action of turning
the note 'on' and 'off' would move the 'hairs' back and forth so the
viewer could actually 'see' which way the air is moving. But would it
help people understand 'how a perforation in a piece of paper gets a
valve to work'?
What most people struggle to comprehend is how the pouch is able
to produce enough power to move the weight of the valve while also
overcoming the level of vacuum that is sucking the valve closed.
The explanation is further complicated when you also tell them that
there's a bleed between the wind chest and the pouch well that is
supplying that same level of vacuum to the underside of the pouch and
the hole in the trackerbar.
Generally, after you also explain that our atmosphere is exerting 14.7
pounds per square inch pressure on everything, the idea that's it's the
'air pressure' that's actually doing the work of moving something (that
only weighs a few grams) within a chamber that has less than 14.7 psi,
begins to start making sense. But how can you 'demonstrate' that which
you cannot see?
Questions that have come to my mind over the years include:
1. Does the square area of the pouch have to be bigger than the square
area of the valve seat?
2. In terms of physical size, is there a finite point at which a pouch
and valve are so big that the pressure of the atmosphere is not great
enough to activate the valve?
3. What is the exact ratio between the size of the bleed and the size
of the hole in the trackerbar at which the note will fail to activate
when the trackerbar hole is open to the atmosphere?
4. What is the exact ratio between the size of the bleed and the size
of the hole in the trackerbar at which the note will fail to turn 'off'
as fast as it turns 'on'?
5. Are there formulas that a person without a degree in physics can
understand that can be used to accurately determine things like the
optimum size of a pouch, valve, a bleed, and striker pneumatic? Or
was it all done by trial-and-error?
What's always fascinated me about player pianos is that there have been
so many different designs that all use exactly the same principles of
operation to perform exactly the same task. Why is that? It seems to
me that if someone had come up with a mechanism that they could prove
was "the best it can be", the effort to "make something better" would
have shortly ceased. However, that's obviously "not" what happened.
In fact, as late as the 1980's, Classic Player Piano was still making
design changes in what was previously the Universal stack -- which is
by far the most compact and air-tight stack that was ever built.
The final question that comes to mind is, would a Plexiglas model that
shows the operation of one valve and pneumatic stimulate a young mind
to the point of asking, 'Why does this thing work?' If not, is it any
more interesting than seeing how a toilet works? (You'd be surprised
how many people don't have a clue as to how their toilet works, and
it's really simple.)
John A Tuttle
Brick, New Jersey, USA