Based on early seventeenth century evidence, principally including the paintings ‘The Artist and his Family’ by Carlo Francesco Nuvolone (1608-1651), and King David playing the Harp by Domenico Zampieri (1581-1641), and also the ‘Kaiser’ harp in Brussels, this type of instrument is almost certainly what Claudio Monterverdi meant by the term ‘Arpa Doppia’ in the score of his opera ‘L’Orfeo’ of 1607.

These instruments have backs of walnut or cherry and soundboards carved from a single plank of sycamore, which gives them a distinctive bell-like tone with good sustain and a loud sonorous bass. They are ideally suited to continuo playing, vocal accompaniment, and the seventeenth century solo repertoire. 

These harps be strung for either A415/A440 or A440/465 .
The large version is tuned GG-e’’’ and the smaller version from
C-e’’’.  A Comparison of the two models is shown below: