Q: How can a speaker create all of the sounds in a song (for example, guitar notes, drums, and vocals) simultaneously?

A: The reason a speaker can create all the sounds simultaneously is the same reason why your ears can hear all the sounds simultaneously. And why a microphone can hear them all simultaneously. That reason is: all the sounds mix together into one very complex sound wave. The sound of each instrument does not travel through a tube separately from the other sounds. Its waves interact and mix with the others because all the air molecules interact with all the waves. A speaker merely reproduces the same vibrating motions as your ears experience when you hear a band live.

Q: If sound is caused by changes in air pressure, then why doesn't my guitar create currents in the air when I strum it?

A: Because air “currents” are one way. Sound waves are two way. Sound waves are not movements of air going in a direction. They are vibrations. The molecules do not migrate from one place to another like wind. They move back and forth a very tiny distance, very rapidly (between 40 times per second and 16,000 times per second.) This creates areas of high and low pressure, and it is those areas of differences in pressure that move at the speed of sound. A 600 mph wind would do a lot of damage! Sound waves move that fast but the air molecules move only a microscopic distance, back and forth, staying on average in the same place! A rough analogy might help: Sound waves are not like a stream of water, where the water moves down the stream bed. They are more like ripples in a pond, where the water stays in one place, but it jiggles back and forth.