Re: Force Versus Distance of a Pneumatic
By Robbie Rhodes
Thanks to John Grant and Craig Brougher and all for the lively discussions and a review of basic physics. Indeed, there are many factors in the player piano which will affect the sound intensity. I'm still compiling a list of all that can happen:
1. The air exhausting from the pneumatic may become turbulent, which reduces the flow rate and hence the rate-of-change of the vacuum within the pneumatic.
2. The force exerted by the striker pneumatic upon the key diminishes as the pneumatic closes -- the force is non-linear.
3. The hammer mechanism (a la Cristofori) multiplies the motion of the key, but this motion-transfer-function is also non-linear.
4. Reducing the hammer travel distance by lifting the hammer rest rail results in the striker pneumatic operating over a reduced span where it is mostly closed, therefore less force. Simultaneously, the hammer mechanism is operating at reduced span, where the mechanical multiplication is less -- it's also non-linear.
All these idiosyncrasies could be reduced to tidy equations, or failing that, plotted on graph paper. Certainly Dr. Hickman investigated many of these problems at the Ampico Laboratory; he wrote equations of physics and also made machines to measure what actually happens inside the player and piano mechanisms.
The analysis of the physics and mathematics is just to make sure we don't overlook some important subtlety. Most important, the researcher who has prepared himself by studying the theory is much more likely to gather experimental data of good value. He is not likely to dismiss an unusual data measurement as "random noise" -- he will search for cause. If the unusual data is really noise, then he improves the experiment setup. Otherwise he will pursue an explanation.
The real world of engineering must balance theoretical efforts (time and money) with empirical methods, in order to solve a practical problem in a reasonable time. So, the next step is to rig up a microphone and oscilloscope at the piano, and gather quantitative data about the relationship of stack pressure to sound intensity for use in the overall transfer functions of the reproducing piano system. It really doesn't matter much what happens in the path between the pneumatic and the sound, as long as the overall transfer-function is reasonably accurate.
In other words, at some point in the project, measuring the real-world actions is better than belaboring the theory.
In still other words (growled by a few former bosses I worked under):
"Shoot the engineer and get on with it!"
-- Robbie Rhodes |
(Message sent Mon 25 Mar 1996, 01:29:37 GMT, from time zone GMT-0800.) |
|
|
Mechanical
Music Digest™ Archives
