Julian Dyer was wondering about roll acceleration in Ampico rolls.
He was wondering why Ampico didn't correct it, etc. when Duo-Art did.
The "acceleration" Wayne Stahnke was referring to is caused by all air
motors' loading characteristics. There was never an air motor built
that doesn't slow down as a load is applied, and as the take-up spool
gets larger while the play brake remains the same, the spool itself
(not the roll) gets slower and slower. So every reproducing piano
company I am aware of took this into consideration.
Even though the air motor slowed down however, the paper sped up faster
than the roll slowed down because the take-up spool's effective diameter
was getting bigger and the angular velocity actually increased a bit.
So on rolls longer than a certain maximum length, they would change the
step advance of the perforator doing the master rolls.
When Wayne spoke of rolls before and after 1925, he was probably
referring to the number of small increments in the way Ampico changed
their step advance. Remember, the Ampico B is able to play those huge
program rolls without noticeable tempo buildup. That amounts to about
three times as much paper as you can put on a Duo-Art, in some cases.
So if there was very much acceleration at all, by the time you had
played 280 (or whatever they are) feet of paper, you would notice a
huge increase in acceleration of the music were it any degree at all
in the beginning.
I imagine a metronome might tell you roughly how well the piano keeps
a constant tempo, but I think you would be, overall, very pleased as to
how even and constant they are, on a practical basis. In other words,
the percent variation from start to finish. It isn't noticeable.
These pianos have performed with orchestras without any trouble at all.
Wayne isn't really criticizing players when he refers to roll
"acceleration." He is speaking as a critical engineer who wants
everything absolutely perfect, so he has to be thorough and is obliged
to carefully check everything out, first. What he measured, few if any
could hear. There are errors in everything. Even the piano which the
Ampicos and Duo-Arts play vary greatly in dynamics, relative dynamics,
dampering, response speed from note to note, etc. These variables are
greater than the variables in the player and from roll to roll.
In regard to the roll transport of Duo-Arts, I have always been a
great admirer of Aeolian's three-point, 6-leaf motor. It is the most
powerful air motor for its size that was put into American players,
and would have the least amount of load de-acceleration of any air
motor, given the right gearing. This Aeolian would have had to make
several more perforator step adjustments than Ampico for any given
number of feet of roll paper, because the roll buildup affected Duo-Art
least of all.
Air motor regulation is maintained with the transmission gearing, once
a no-load speed is selected. The tiniest air motor I ever saw is in
the Apollo Art-Echo grand. It is about 5" long, with 4 tiny little
bellows not even an inch wide and probably 4" long (from memory). Yet
it does quite well, and hauls about any roll through the system nicely.
[ Some pop songs bother me when the music accelerates, and some
[ songs don't. Both my Ampico B and the Duo-Art pumper have excellent
[ motor-speed regulation, and the effect is the same with either piano
[ -- I find that I slowly push the Tempo down with my thumb or finger
[ so that the music doesn't accelerate. A 3-minute pop music roll
[ which begins at Tempo 100 is slowly decelerated, ending at Tempo 95,
[ for example. Some songs bug me, some don't. -- Robbie