We combine two concepts, the musical instrument as metaphorand technology probes, to explore how tangible interfaces canexploit the semantic richness of sound. Using participatorydesign methods from Human-Computer Interaction (HCI), wedesigned and tested the A20, a polyhedron-shaped, multichannel audio input/output device. The software maps soundaround the edges and responds to the user's gestural input,allowing both aural and haptic modes of interaction as well asdirect manipulation of media content. The software is designedto be very flexible and can be adapted to a wide range ofshapes. Our tests of the A20's perceptual and interactionproperties showed that users can successfully detect soundplacement, movement and haptic effects on this device. Ourparticipatory design workshops explored the possibilities of theA20 as a generative tool for the design of an extended,collaborative personal music player. The A20 helped users toenact scenarios of everyday mobile music player use and togenerate new design ideas.