Following up on Spencer's posting about electric vacuum pump noise, I
downloaded the patent for the Motor Player Company vacuum pump. It is
quite an interesting device. A series of baffles for intake and
exhaust air appear to be surrounding the turbine and the motor.
According to the description in the patent, the baffles are covered
with felt, which appears to be about 1/8" thick.
One of the problems that concerned the inventor was keeping the motor
cool when very little vacuum was needed to operate the player system.
So he devised a bypass. With a variable speed pump, it would seem
that such a device would be unnecessary because even in rewind mode,
the windmotor is using some amount of air.
I fully admit that I don't understand the physics of sound dampening,
vibrations of different frequencies, converting sound to heat, etc.
However, based on what appears to be the relatively straightforward
baffle design in the patent, creating a cylindrical "muffler" doesn't
look like it will be too difficult. Unless I'm missing something, it
looks like the goal is to force the air to run into a wall that has a
soft, sound absorbing material mounted to it, forcing the air to change
direction (90 degrees), and running it down a channel until it is
forced to change direction again about three or four times.
Any input here?
John A. Tuttle
[ John sent in the patent as a PDF file. It is patent 1,565,932,
[ granted Dec. 15 1925 to C.H. Hanson (filed May 24, 1921) and titled
[ "Means For Actuating Player Pianos."
[ --Relief Editor.