Roll Harmonica
By Ed Schmidt
Spencer Chase wrote:
> There are little valve-like flaps that always seem to be curled and
> dried up. I have replaced these with light weight motor cloth but
> have no idea what their function actually is. They don't really seem
> to be capable of acting as valves which they appear to be. Maybe the
> original material had just the right stiffness to act as a valve and
> may have allowed the Rollmonica to work as well under suction as
> under pressure. Any ideas about what material to try or what the
> little things really are?
The "little valve-like flaps" are indeed valve flaps. The valve serves several purposes. Since the reeds in harmonicas and accordions can be activated with either pressure or vacuum, two reeds are employed for each note. Each reed is constructed to sound when air passes in only one direction. However, some reeds will sound with air passage in both directions.
When this occurs, if one reed of the pair is not blocked, both will sound. If both sound, they must be tuned to exactly the same frequency or beats will be heard. It is much more difficult to hear very small differences in frequency when the notes are sounded in sequence than when they are sounded together. Thus when you suck or blow (push or pull) you think you hear the same frequency. So the solution is to alternately cover one reed as you suck or blow.
Another reason for the valve is to reduce the volume of air required to operate the instrument. If the second reed of a pair did not sound when you blow, air would still be passing through the reed frame and around the reed. This air has to be supplied by the operator, so you might have to blow twice as hard if the flap valves were not present.
I have used pneumatic leather, either the natural, or tan on instruments like the Tanzbar accordion. I attach the leather with a drop of Krazy Glue designated for leather.
Ed Schmidt <eschmidt@erols.com>
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(Message sent Fri 7 Mar 1997, 13:19:51 GMT, from time zone GMT-0500.) |
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