Observations and results
Why did you have a much harder time hearing the sound when the string was wrapped around your helper's head than when it was wrapped around yours?
When you pluck on the string that's wrapped around your helper's head, the string starts vibrating. To reach your ears the vibrations in the string must push on the air to make sound waves that travel through the air. But the string isn't very large and it doesn't push on very much air so sound vibrations don't travel easily from the string into the air.
When the string is around your own head, however, the sound can take a more direct route to your ears. Rather than traveling through the air, the vibration can travel through your hands and skull bone directly to the fluid inside the cochlea in your inner ear. Instead of traveling from solid to air and back to solid, the vibrations move from one solid (the string) to another (your body) then into the fluid of your cochlea. As a result, the sound you hear is much louder and richer.
In vibrating strings there is a relationship between tension and vibration speed of waves in the string. So the pitch you hear is a result of the string tension; the tighter the string the higher the frequency of vibration. This high tension creates a tone with a high frequency. For a less tense string the reverse is true: lower frequency vibrations translate into the perception of a lower tone.
More to Explore from Exploratorium
Ear Guitar, from Exploratorium
Sound Bite: Listen with Your Head Bone, from Exploratorium
Find That Sound, from Exploratorium
Science of Music, from Exploratorium
Harmonies in Your Head was developed by Exploratorium and is featured in the book Exploralab: 150+ Ways to Investigate the Amazing Science All Around You. Created by Exploratorium, Exploralabis a book that takes curious kid scientists, ages eight to 12, through 24 hours’ worth of household investigations, experiments and discoveries.