Sound production with a single reed and mouthpiece begins with the player. The player blows air past and over the reed into the mouthpiece. This provides a constant source of energy. Once the difference in pressure between the mouth and the mouthpiece becomes great enough, the reed bends and closes (partially or completely) the mouthpiece. Then, the elasticity of the reed acts to re-open the gap between reed and mouthpiece. This cyclical motion produces a compressional wave that travels down the length of the instrument to the first open hole. When it meets this border with the atmosphere, some of the wave continues outward and into the surroundings. The rest of the energy from the wave reflects as a rarefaction* back up the instrument. As soon as this wave reaches the mouthpiece, the process repeats to start the process all over again. The reed vibrates back and forth between alternating high areas of high pressure in the mouth and in the mouthpiece. Based on the length of the closed tube, this process repeats hundreds of times a second.
Reeds v. Lip Reeds
*Rarefaction: reduction of the density of a wave
Sound production with a lip reed also begins with the player, but it does not involve a physical reed. Instead, the lips of the musician act like a reed to convert the steady stream of air into waves. First, the musician blows air through the mouthpiece, opening an aperture between the lips. Due to the elasticity of the lips, they quickly snap back into place. This produces a compressional wave of air that travels all the way through the instrument. When it reaches the bell, some energy transmits and some reflects (again, in the form of a rarefaction*). Once the rarefaction reaches the mouthpiece, the lips open again, releasing another compressional wave of air. The cycle stabilizes based on the length of the pipe, occurring hundreds of times every second.
These sound files are recordings of scales played just on the mouthpiece of each instrument. They demonstrate the result of sound production by reeds and lip reeds without the complication of the instrument.