Make a string telephone
Join two cups with string, listen with a partner, and find out what interrupts the sound.
About this project
Two cups and a string make a connection you can see and touch. Set up a short line with a partner, then listen to what happens when that line changes.
Supplies
Materials & tools
- Two clean paper cups with prepared center holes
- About 2–3 metres of light string that passes through the holes
- Suitable scissors for cutting the string
- A partner and enough clear space to stand or sit apart
Before you start
- Ask someone who knows the tools to make a small, smooth hole in the middle of each cup bottom. Rest the cup on a supported surface while making the hole. Do not push a pencil or scissors through a cup held in a hand.
- Find a clear space where no one needs to walk across the string. Keep string away from necks and never wrap it around a person. Give each person their own clean cup.
Instructions
Attach the string inside one cup
Push one end of the string through the hole from the outside of the cup into the inside. Pull about 10 cm through. Tie a thick knot in this short end. Gently pull the long string from outside. The knot should rest against the inside bottom without coming through the hole. Make the knot thicker if it slips through.
Attach the other cup
Put the other string end through the second cup from outside to inside. Tie and check the knot in the same way. Pull gently on each connection. If a hole tears or the knot keeps coming through, replace the cup or ask your helper for a smaller hole.
A knot inside each cup holds the string. Leave the string free between the cups, gently taut rather than pulled hard. Move apart until the string is straight
Each person holds a cup by its sides. Move apart until the loose bend in the string disappears. The string should be gently stretched, not pulled hard. Keep it clear of chairs, tables, and hands. Leave the cup bottoms free to move; do not press on them with your fingers.
Speak and listen
One person speaks toward their cup’s opening at a normal volume. The other listens near their own cup’s opening. Do not put a cup against your mouth or into your ear. Take turns. Then move closer so the string hangs loose, or have someone touch its middle lightly. Listen again if you want to compare the sounds.
Troubleshooting
- You mostly hear the voice through the room.
- Try a quiet voice in a quiet space. Listen once with the string straight and once with it hanging loose. Check that it is not touching furniture and that no fingers press on the cup bottoms.
- Little or no sound reaches the other cup.
- Check both knots. Move apart gently until the string is straight. Look for anything touching the string. If these connections look right, try another string or cup.
- The cup bottom starts tearing.
- Stop pulling and replace the cup. Pulling harder can tear a bigger hole instead of helping the sound.
Where to take it next
- Try a different type of string or a different cup and describe what you hear.
- Have a third person touch the line with a fingertip or a soft object while the partners listen.
- Try taking the line around an object, away from walkways. A corner or contact point may change or stop the sound.
A closer look
A voice makes the cup bottom move back and forth very slightly. This movement is called vibration. A gently stretched string can carry it to the other cup, whose bottom moves the air near your ear. A loose string or something touching it can change that movement. The knots, string, and both cup bottoms are all part of the connection.
What happens if…
- What changes when you touch the string?
- Where might the sound be getting lost?
- What would you try with a third person?
What it needs to do
A function can have more than one solution. These options belong to this example; try alternatives thoughtfully.
vibrating surface
Two clean paper cups with small holes prepared safely by an experienced helper. Cup stiffness and connection details may change the result.
vibration path
Enough clean string for a short, clear space. Keep it gently taut without pulling the cups hard.