3A60.XX Breaking Glass with Sound
Resonance, standing waves in 2D
A large speaker is driven by a function generator and an audio amplifier. When the speaker excites a wine glass at resonance, the glass oscillates and may break. A strobe light makes the oscillations easier to see.
-  Wine glass
-  Paper riders
-  Foam isolator
-  Plexiglas shield
-  Speaker
-  Steel brick
-  Audio amplifier
-  Speaker wire
-  Function generator
-  BNC cable
-  BNC to RCA adapter
-  Oscilloscope
-  Microphone with holder
-  3.5 mm to BNC adapter
-  Lab stand
-  90-degree clamp
-  Lab jack with sidewalls
-  Strobe light
-  Video camera
- Power bar
-  Earmuffs (for the instructor)
- Earplugs (for the class)
- Mount the speaker on the lab jack, with the steel brick as a backstop.
- Connect the speaker to the amplifier.
- Put the wine glass on the foam isolator and adjust the speaker height so that the middle of the speaker is level with the rim of the glass.
- Mount the microphone on the lab stand using the 90-degree clamp. Make sure it's close to the rim of the glass.
- Connect the microphone to the oscilloscope using the 3.5 mm to BNC adapter.
- Put the Plexiglas shield around the speaker and wine glass.
- Set up the strobe light on top of the shield.
- Connect the function generator to the audio amplifier using the BNC cable and the BNC to RCA adapter.
- Set up the video camera for a good view of the rim of the glass.
- Connect the video camera to the room projector.
- Plug everything in.
- Test the setup and find a good strobe frequency for viewing the oscillations.
- Strobe lights can cause seizures in some people. Make sure no one in the class is sensitive to them.
- Loud noises can cause hearing loss. Everyone should wear hearing protection or cover one's ears.
- Do not go over the rated power for the amplifier. Otherwise, it will destroy the outputs.
- Hand out earplugs to the class and wait for them to wear them.
- Make sure no one in the class is sensitive to strobe lights.
- Put on your earmuffs.
- Put paper riders on the wine glass rim.
- Turn on the function generator, the amplifier, the oscilloscope, and the video camera. Increase the function generator signal to 100 mV RMS and increase the amplifier gain.
- Scan the function generator frequency for the resonance of the wine glass. Use the microphone signal on the oscilloscope as a guide to getting close to resonance. The riders should start shaking.
- Turn on the strobe light and scan the strobe light frequency for the best visibility of the oscillations.
- Try to find resonance. If you're lucky, the glass will break.
- Turn everything off.
- Take off your earmuffs.
- PIRA 3A60.XX
- Don't attempt this at home!
- The best wine glasses for this don't have a thick rim, which makes it harder for them to break. Apparently, they're called "crystal." You can cheat a little by making a tiny imperfection in the glass using a file.
- Our speaker is rated to 1000 W, but the amplifier can only output about 100 W. If you know where to find a proper driver for the speaker, please email Ricky (contact info at the bottom of this page).
- The earplugs come from Science Stores.
- PhysicsGirl has a good video on her experience trying to break a wine glass with only her voice!
If you have any questions about the demos or notes you would like to add to this page, contact Ricky Chu at ricky_chu AT sfu DOT ca.