The invention relates to a musical instrument having free reeds set into
vibration by a flow of air generated by a supply (17) and capable of
flowing from the supply in two directions referred to respectively as in
and out, the instrument comprising: at least two boxes (2, 3) that are
movable relative to each other by moving towards each other or apart from
each other; a series of free reeds (27) mounted inside said boxes; and a
valve actuator mechanism (31) where opening and closing the valves
enables the reeds to be engaged or not engaged by the flow of air, the
mechanism including in particular actuator keys (11) mounted on the
moving boxes. The instrument of the invention includes means (5) for
supporting and guiding displacement of the boxes relative to each other
along a determined trajectory.