Muro Box, a music box that plays the tunes you choose

One tune finishes, and you choose another without changing the music box. Muro Box lets you select a melody through an app. Instead of playing a recording through a speaker, it makes sound by physically plucking the teeth of a metal comb inside.

In a traditional cylinder music box, small pins on a rotating cylinder pluck the comb. Their positions determine the sequence of notes, so another tune requires a different arrangement. Muro Box's developers set out to change that cylinder: control when its pins act, and the same mechanism can play different tunes.

The development records show a prototype with twenty controls, each governing when one note is plucked. Electromagnets and controllers send commands to the rotating mechanism, but vibrating metal still produces the sound. Electronic control changes the sequence and timing of the plucks, rather than selecting an audio recording.

That does not mean it can reproduce everything you listen to on a phone. The N20 has twenty notes and does not include every semitone. The manufacturer says notes outside its range are omitted, while unavailable notes within the range are adjusted. More complex pieces may need rearranging for the notes the instrument can play.

Input options vary by model. The official guide says all models support Bluetooth MIDI, while USB-C MIDI input is provided on the N20 Standard and N40 models, but not the N20 Lite. MIDI is information about which notes to play and when, rather than recorded sound. A file sending instructions to the music box serves a different purpose from an audio recording.

The little box does not acquire a new comb for each song. It changes the sequence of its limited set of notes. Choose a tune in the app, and the mechanism inside moves to that tune as the comb sounds.