The three branches of the woodwind family have different sources of sound. Vibrations begin when air is blown across the top of an instrument, across a single reed, or across two reeds. Reeds are small pieces of cane. A single reed is clamped to a mouthpiece at the top of the instrument and vibrates against the mouthpiece when air is blown between the reed and the mouthpiece. Two reeds tied together are commonly known as a double reed. This double reed fits into a tube at the top of the instrument and vibrates when air is forced between the two reeds.
The bassoon is a large double reed instrument with a lower sound than the other woodwind instruments. Its double reed is attached to a small curved tube called a bocal which fits into the bassoon. When the player blows air between the reeds, the vibrating column of air inside the instrument travels over nine feet to the bottom of the instrument, then up to the top where the sound comes out.