A melodeon works by pushing or drawing air through sets of fixed reeds, the flow of the air being controlled by the bellows being pushed together or pulled apart,
valves fitted to each reed allowing only one way air flow, and a key operated paddle which opens of blocks the airway to a reed. Each airway typically services two reeds, one set to sound when
the bellows are pushed, the other when the bellows are pulled. The actual action of pushing or pulling the bellows produces either higher or lower pressure inside the bellows which produces the
air flow when a path to the outside air is made with the key operated paddle. The musician can dynamically vary the volume of the instrument using the bellows to either effect an overall volume
increase or to produce a vibrato effect, as well as producing very long or short notes with a dynamic suited to the music. The key/pallet mechanism determines which notes will sound but have only
a coarse effect on the dynamics of the sound but will cutoff the sound suddenly. A further dynamic is that the reeds do not start to sound until a specific amount of air is flowing over them, but
once vibrating, will continue to sound after the air flow has dropped below the volume required to start the vibration. Lastly, a air button is present which opens a valve to the bellows
effectively making the pressure inside the bellows equal to that outside and allows the bellows to be opened and closed without a reed sounding. A player may incorporate the use of the air button
to selectively soften the playing of a note, or to enable a note to be played while positioning the bellows in preparation for the playing of a long sequence of notes requiring the bellows to be
moved in a single direction.
The instrument has two keyboards, one for the melody, normally played in a fixed position, and the bass section, which the player moves to expand and compress the
bellows. The bass keyboard comprises fewer keys, and consists of reeds playing either notes from a lower octave to the melody, or chords associated with those notes.