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MMD > Archives > February 2011 > 2011.02.17 > 03Prev  Next

By John A. Tuttle

Hi All,  My quest to figure out exactly how the Piano-Lodeon works
continues.  I finished a graphic that accurately shows the placement
of the two 'vanes' in the plenum.  It's located at 

Today, I tried to measure the vacuum level inside the plenum without
any success.  Naturally, my immediate thought was 'this isn't
possible'.  Closing off all of the ports on the trackerbar with tape,
I disconnected one of the tubes and hooked up my vacuum gauge.  The
pointer didn't move at all.  Not even slightly.  So, I tested it using
my tongue, which I believe is pretty sensitive to vacuum.  Indeed,
I felt something, but it was an extremely small amount.

All of this made me stop and think.  While the system most definitely
utilizes vacuum to do the work, it must be more about 'air flow' than
'vacuum level'.  I know that might sound a little odd since the unit
definitely uses vacuum, but I believe it got me thinking in the right
direction.  The next thing that came to mind was the flue in my forced
hot air furnace.  (You say, "What?") Then I thought about a carburetor
and the 'venturi effect'.  Air passing over an orifice will create
a partial vacuum - and 'lift'.  Now I was getting someplace.  (huh?)

So I checked Google to find out how fast wind would have to be
moving over a closed-end pipe to create any vacuum in the pipe.  As
I discovered, the term 'flow rate' comes into the picture.  And, if
I read the charts correctly, about 1/2" of vacuum (in H2O) is created
by a 20 mph wind.  So, I started thinking about the plastic vanes in
the Piano-Lodeon and how much 'wind' it would take to get them to move.
Unfortunately, I don't have an anemometer.  But as I had demonstrated
in my YouTube video (see link), it only took a whisper of air to get
the 'valve vane' to open.  (I know... what's a whisper of air?) 

All of this thinking was making me tired, so I took a nap - no just
kidding....  I started thinking that perhaps the basic operating
principles used in this instrument weren't nearly as similar to a
pneumatic player as I originally thought.  In fact, maybe they were
quite different altogether.  The more I looked at it, the more I felt
the need to start over at square one.

While it's true that the mechanism utilizes vacuum to function and it
has a trackerbar, those are about the only two things it has in common
with a pneumatic player action.  It doesn't have pouches, bellows, or
air-tight valves.  So, how does it work?

About the easiest way to explain it is to say 'it's a balancing act',
and it functions by 'upsetting the balance'.  Think of a 'balance beam
scale'.  When weight is put on one side, it causes the beam to move.
Naturally, depending on the sensitivity of the scale, adding a certain
amount of weight will cause the beam to move to its furthest extreme.
Adding more weight will cause it to move to that extreme faster, and so

Now, consider that 'moving air' exerts a certain amount of force on a
balanced 'vane'.  You begin to get the picture, and understand that it
doesn't take a whole lot of moving air to cause the vane to move.  And,
if you increase the air flow, the vane will move even faster.

Also, we have to understand that the weight and mass of the vane
play a critical role in determining the 'rate' at which the vane will
accelerate over a given period of time and distance.  This is important
because the goal of moving the vane is to develop enough inertia (or
power) to move another device, which will strike a tine.

(Let me stop at this point and admit that I'm not a physicist.  I don't
know the formulas that are needed to prove anything I'm saying.  This
treatise is my way of looking at the device and trying to make some
sense of how and why it works.  Hopefully there is someone in the group
who can actually explain the principles of operation in scientific

So, putting this all together, let's see what happens in the Piano
Lodeon.  Unlike a balance beam scale, that is stationary between two
extremes when balanced, the vanes in the Piano Lodeon are heavier on
one side of the fulcrum point than the other.  In both cases, the vanes
are 'weighted' such that the 'atmosphere' side (or the side that's not
in the plenum) is in a 'down' position when at rest.  And, both of them
stay in that position even when vacuum is applied to the plenum, as
long as trackerbar hole is closed.

Once the trackerbar hole is opened by a perforation in the music roll,
atmosphere rushes down a tube and blows on the 'valve vane', which
causes it to open.  That action opens a much larger orifice, which
allows a large amount of atmosphere to enter the plenum, and that air
blows the 'striker vane' through its entire range of motion.  Now
here's where it gets a little more interesting, and I think I've
finally figured it out.

After the perforation passes, both vanes return to their resting
point.  But there's one more piece of the puzzle that had me a little
baffled.  That was the hole in the striker vane.  (You might have seen
it in the video.  It's a 5/32" hole in the inside portion of the vane.)
Determined to know why it was there, I performed a little experiment.
I took a tiny piece of Scotch tape and covered the hole.  Then I tested
two notes; the one with the taped hole and one without the tape.

Sure enough, the one with the tape returned to its resting point (when
the trackerbar hole was closed) more slowly than the one without the
tape.  So, the function of the hole is to allow the vacuum to equalize
more quickly in the plenum.  I guess you could call it a 'bleed'.

One other point that has some relevance concerns the striker vane and
its associate chamber.  The vane is 0.460" wide and the chamber is
0.470" wide.  Also, the length of the vane (inside the chamber) is
0.005" shorter than the overall length of the chamber.  Ergo, there is
0.005" clearance on all three sides of the vane inside the chamber.
Considering that the vane is exactly 2-1/2" long, the total area
through which air can pass is 0.0273 sq. in.  And, the area of the
5/32" 'bleed' hole is 0.0192".

So, it seems obvious that the spacing around the vane, which also acts
as a bleed when the vane is returning to its resting point, was about
70% of what the designer/manufacturer felt was needed to achieve a
sufficient repetition rate.  Frankly, taping over the hole in the vane
didn't make much of a difference in the return speed.  So, I don't know
if making the hole bigger would have made a noticeable improvement.

In closing, I'm more than open to any ideas and/or thoughts that anyone
has concerning this mechanism.  Perhaps someone can explain all of this
in a much more succinct manner.  If more details about the parts are
needed, I will do my best to provide them.

John A Tuttle
Brick, New Jersey, USA

(Message sent Thu 17 Feb 2011, 17:54:39 GMT, from time zone GMT-0500.)

Key Words in Subject:  Piano-Lodeons

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