Duet concertina

Duet concertinas are unisonoric, and are similar in outward appearance and construction to the original English concertina, except for the arrangement of the hand rests and straps, which more closely resembles an Anglo concertina.

The button layout is altered so that the high notes are played on the right and the low notes on the left. This makes it easier to play a melody with an accompaniment. There are several keyboard systems available:
 * MacCann duet
 * Crane duet
 * Triumph duet
 * Jeffries duet
 * Hayden duet
 * Wheatstone systems:
 * Wheatstone Double
 * Wheatstone Duett
 * Wheatstone Chidley

The Hayden system is the most recent development, invented by Brian Hayden.