Besides physical structure, what is the difference between a curved and a straight windway in a recorder? I understand that a curved windway increases air resistance, but how does the sound quality compare in the two?
Curved windways are usually considered to give a more interesting, complex tone quality, but I couldn't give an acoustic reason for this. They're definitely more difficult to produce I've also heard it suggested that a curved windway is superior because it allows condensation to drain to the edges of the windway more easily, where it will interfere less.
For the commenter asking what the windway is:
Credit: Daniel Bingamon, Jubilee Instruments & Crafts.
When you look at the mouthpiece end of a recorder, the windway is the narrow slot that you blow into. Transverse flutes don't have a windway, or more precisely, the windway is formed by your mouth and lips directing the stream of air over the embouchure hole.
This picture shows a curved windway: