When they think of the hurdy-gurdy, the mind of most people conjures up
an Italian man with a little barrel organ or piano and a monkey along
the sidewalk.  The word originally refers to a hand-played instrument
that goes back to the middle ages.  It's sort of a stringed version of
the bagpipes and is also known as a 'vielle a roue' or 'lyra'.

It's basic construction is that of a bowed instrument.  A wooden wheel,
turned by a crank, bows the strings from underneath.  Two sets of
strings on the side of the wheel are drones and another set, on top,
are the chanters which are fretted by rows of buttons along the side.

By the late Middle Ages, it was the favorite instrument of street
musicians and beggars.  In the 18th century, with the Pastoral craze
egged on by Marie Antoinette, some very fine instruments were made for
the nobility.

I have a little theory based on many of the instruments I've seen from
this period.  Around the end of the 1600's, they started adding pipes
that played in unison with the chanter strings.  Then I have seen an
example of one that had a pinned cylinder.  Now, the strings of a
hurdy-gurdy, like bagpipes or any instrument played outdoors, are very
unstable and require tuning and adjustment constantly.

Could it be that they discovered the pipes to be more stable and just
decided to do without the strings, so we have the hurdy-gurdy as we
know it today?

I make the medieval version of this instrument. You can see a picture
of me playing one.

Brian Thornton - Short Mountain Music Works
Woodbury, TN  37190
http://www.mindspring.com/~goatboy/smmw.htm