Shattering glass with sound (Experiment 1)

So I decided to set up a speaker to try and shatter a wineglass with sound waves. Opening up the cupboard, I found an old wineglass with thin walls. Perfect.

Then to get the natural frequency of the wineglass... I set up an amplifier and microphone, with the output of the amp connected to the oscilloscope. Placing the microphone next to the wineglass, I 'pinged' the wineglass and captured the oscilloscope waveform. This enabled me to find the approximate frequency.

Being a musician of some sorts, I had guessed about right anyway. The natural frequency was found to be ~1170 Hz, just a tad high for a wineglass but who cares. I entered this value into a frequency synthesizer and connected a horn speaker to the output of an old 6W amplifier.

Setup is shown to the right.

Initially setting the volume quite low, I used the same microphone-oscilloscope setup on the other side of the wineglass to check for resonance. At 1170 Hz, the wineglass was vibrating, but not enough. Trailing values from 1160 to 1180 Hz showed that maximum vibration occurred at 1168 Hz. I had found the exact natural frequency.

I plugged this value into the synthesizer and spun all intermediate volume control sliders to max. Video camera was set up outside the blast box to capture some of the action.

Lights, camera, action....

Download the raw video capture HERE [1.4mb MPEG]

Download the noise reduction video HERE [0.8mb WMV]

Don't forget to turn up the sound! Otherwise you probably won't even know when it breaks...(The noise reduction version enables you to hear the glass shattering more easily, but the raw capture gives an idea of how loud the 1168 Hz tone is).

The poor old shattered wineglass. If you watched the video, you would have seen the little paper bits that jumped off the wineglass before it shattered. Those paper bits indicate magnitude of vibration, and the glass shatters soon after the vibrations are strong enough to throw the paper off.

Unfortunately, as soon as the glass fractures, it no longer resonates at the same natural frequency and doesn't 'ping' anymore, so there is no further destruction other than the possibility of smashing it on the ground.

A better view of the internal fractures in the glass. The main fracture actually extends almost right around the goblet.

The speaker behind is not the horn speaker, in case you were wondering.