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Websites we've worked on:
Sound tourism map link
sound around you link
sound101 link
Dr Andy Moorhouse on piano ...

BBC radio docs on sound:

- presented by Prof Trevor Cox

The best way for breaking glass with sound

Third experiment

For the main glass breaking page, click here, it is recommended you read the main page first. You might also want to view the second experiment.

loudspeaker and glass

The problem with breaking the glass using a large loudspeaker, is that you excite the glass in a very inefficient way. The left diagram shows the simplest vibration mode of a glass viewed from above. Consider the dotted line, to be efficient, the air must be causing the left hand edge of the glass to move leftwards, and the right hand edge to move rightwards - both sides must be being stretched. However, the wavelength of sound is much greater than the size of the glass, so in reality the air on both sides of the glass is trying to move the glass in the same way. This is why the excitation is so inefficient. If you view the top-view of the glass with the high speed camera here, then you can visualise what is going on. But this inefficient excitation can be overcome.

Compression driver and loudspeaker

A compression driver is used. This is a loudspeaker with a very small diaphragm, which along with a small tube can be used to direct the sound onto one side of the glass. Most compression drivers come with a range of adaptors, and so you can use one of these as the small tube. The right side of the glass is now shadowed from the sound by the rest of the glass, and so it is easier to break the glass because the sound on the right is hindering the vibration of the glass less.

We used a Fane CD280 compression driver, but many different companies make suitable devices. You'll need a 2" compression driver because the more normal 1" designs probably don't go to a low enough frequency for the glass resonance. Apart from that, we used the same tuning methods described in experiments 1 & 2.

Warning, when the glass breaks it can send glass everywhere. You need to wear safety goggles.

glass breaking View high speed footage of breaking glass (on our Schools' site)

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