Re: Why does an oboe reed have to be wet in order to produce sound?

Music, like all sounds, is made up of vibrations travelling through the 
air. Musical instruments create their characteristic sounds according to 
their shape, how the vibration is started off and the amount of air forced 
to vibrate.

Single reed instruments like the clarinet and saxophone use a reed of 
springy cane fastened at one end over a hole in a mouthpiece to start the 
vibrations going. The reed responds to breath pressure by beating against 
the hole many times per second, allowing puffs of wind into the tube to 
vibrate the enclosed air. 

The oboe and the bassoon are double-reed instruments which produce 
vibrations when two slender blades of cane pinch together rapidly under 
breath pressure, thus interrupting the wind stream passing between them 
into the rest of the instrument.

Dry reeds are very stiff and difficult to set vibrating, on a clarinet you 
have to blow very hard and will make harsh sounds as a result and on an 
oboe, with two dry reeds next to one another, it would be nearly impossible 
to make a sound. When wet the reeds soften and become more flexible, they 
can bend to and fro more easily and so can be made to vibrate under more 
gentle breath pressure. This allows the oboe player to produce a hauntingly 
beautiful range of tones.

Reference source: Microsoft Encarta 99