Introduction to the Science of Sound You’ve probably hung around large speakers and you’ve probably noticed how the speaker moves when it plays a low note. When that happens the speaker is compressing the air around it, which raises its pressure. This pressure transfers through the air creating a sound wave. The same thing happens when the string on a guitar or violin vibrates.  As the pressure changes the molecules in the air oscillate back and forth. The speed of this oscillation is what we refer to as the frequency.