Thanks for sharing the results of your very interesting experiment, Ofir. (Lovely playing, by the way.) I have a few questions:
(1) Is the piece of wood held solidly in place by being compressed between the two plastic surfaces?
(2) Do you anticipate having to change it out periodically because of the affects of moisture?
(3) Have you thought about the possibility of adding something to the reed chamber. I know there is very little space for that in a Yamaha. A strip of some kind of tape, maybe, or a thin layer of, say, adhesive backed felt.
I’m supposing that felt would mute the sound, but I’m just mentioning that as an example of what might fit in the reed chamber and alter the sound (and/or reduce the size of the chamber).
I’m not an engineer, but I’m guessing that the vibration is due to the increased contact via the wood strip between the reed chamber cover and the main tray of the Pianica, as contrasted with a buffer of air?