Our keyboard is built physically with a wood structure, which supports a sheet of plexiglass attached with screws. On the plexiglass surface the design of the keyboard, printed on cardboard, has been glued. On two supports, also of wood, were both placed the receiver, fixed at a precise distance from the beginning of the keyboard, and the transmitter, that instead can move rigidly along the axis in front of the keyboard, thanks to two aluminium bars fixed to the structure. Since receiver and transmitter are placed inside the top face of the wooden cubes that support them, and not on the edge, problems of reflection of the acoustic signal against the plexiglass floor below are avoided.