The fantasy musical instruments that appear in the films, "Pirates of
the Caribbean", were originally meant to be circa 1740 or even a bit
earlier, as it is known that no such instruments as these had yet been
invented during that time, hence the "fantasy" aspect comes into play.

The first musical piece seen in Pirates 2 was a "crab" formed into a
heart-shaped silver pendant.  On the back of the crab is 'just visible'
the face of a young woman.  This piece was first seen on a table in the
hut of Tia Dalma, played by Naomi Harris, in Pirates 2 ("Curse of the
Black Pearl").  The next time you see the pendant it is next to the
keyboard of Davy Jones' (Bill Nighy) and his "fantasy" pipe organ.

The music box pendant was essentially a barillet style mechanism that
had two counter-rotating pinned barrels that played on two tiny combs.
This pendant music box is spring wound.

As regards the large instrument appearing in Pirates 3 ("At World's
End") in a scene in Singapore, this piece most closely resembles a
mechanical harp, or a plucked zither, with the musical program carried
on a large pinned barrel.  The strings of this instrument were designed
to be plucked by articulated plucking fingers, and there were no hidden
pipes, nor was it originally meant to be spring wound, only cranked.
So, if indeed it appeared to be spring wound, complete with organ
music, then this is most likely where a bit of Hollywood magic comes
into play.

Hope this helps you to understand two of the musical items in these
two films.

Christian Eric - Antique Music Box Restoration
Costa Mesa, California