Harriet’s String Band

Harriet’s cardboard-box band is ready for the class performance, but every note sounds much the same. She plucks harder, hoping for a higher sound. Mr Reed listens. “That changed something,” he says. “Was it the pitch, or how loud the sound was?” Harriet wants to find out.

They watch one thick rubber band while Harriet plucks gently over the box opening. It vibrates, moving backwards and forwards. Vibrations make the sound. The box helps pass those vibrations to the surrounding air. Harriet can hear the note without seeing the air moving around her.

Harriet lightly touches the moving band. Its vibration stops, and the sound fades. “The movement mattered,” she says. Mr Reed checks that the bands are undamaged and not stretched too tightly. They keep the instrument on the table, well away from faces and ears.

They put a small movable bridge beneath one band. It leaves a shorter section free to vibrate when Harriet plucks it. She compares that section with a longer section of the same band. They try to keep its tension and the way they pluck it similar.

The shorter vibrating section gives a higher note in their comparison. The longer section gives a lower one. Pitch describes how high or low a sound is. Faster vibrations usually produce a higher pitch. Harriet slides the bridge carefully and listens for the change again.

Harriet records which section sounded higher before moving the bridge. She repeats the comparison rather than trusting one quick pluck. Band thickness and tension can also affect pitch, so their simple investigation does not explain every difference between all string instruments. It answers one narrower question.

Next she plucks the same section softly, then a little more firmly without changing its length. The firmer pluck sounds louder. Loudness and pitch are different features, although changing an instrument carelessly can affect both. Harriet stops trying to make every high note by pulling harder.

At the performance, Harriet uses the bridge to choose notes and gentle plucks to keep a comfortable volume. Her friends join the tune. Mr Reed asks what helped. “Listening to one change at a time,” she says. The cardboard band finally has more than one note to play.