Breaking Glass with Sound, 3D40.55

Location:

• Cabinet: [:WavesSoundCabinet:Waves & Sound (WS)]

• Floor Item

attachment:GlassBreaker-01-400.jpg

Description:

A large 2" compression driver with horn is used with an audio amplifier to break glassware/stemware at its resonant frequency. An adjustable function generator is used to deliver a pure tone. A strobe light can be added to show the oscillations of the glass before it shatters.

Important Setup Notes:

1. This demonstration requires a minimum 10 hour notice.

2. This demonstration requires Stemware

3. Practice is a must! Every glass is different.

4. Requires an operator with a good ear for sound

5. Requires a camera

6. Slow Motion Video or Camera is Available

Setup:

1. Set large box out, visible to audience.
2. Connect the speaker to an output of the audio amplifier
3. Connect the function generator to an input on the audio amplifier
4. Firmly tape the stemware to the steel brick and place in box as close to the speaker as possible.
5. Make sure that the stemware isn't too high. The top third of the horn should be above the stemware.
6. Make a paper feather out of a post-it note and stick it to the rim of the stemware, so that the paper feather can vibrate at the resonant frequency of the glass.
7. With the speaker at a very low volume, rapidly tap the stemware with a tuning fork mallet and adjust the function generator to narrow in on the resonant frequency.
8. Slide the front cover closed and shim it in place to prevent the cover from vibrating.
9. Set up a strobe light and/or cameras if necessary.

Cautions, Warnings, or Safety Concerns:

1. Broken Glass is Very Very Sharp....
2. Sound within the box can reach 140dB.
3. Glass may not break!
4. Glass could shatter while you find resonance.
5. Use duct tape to pick up shards of glass.

Demonstration:

Breaking stemware or glassware is a bit of an art and can be tricky to do. With this equipment and setup, we're able to break most any type of glassware, from Pyrex beakers to tall beer schooners. The more lead in the glassware the better it is, but cheap glass that makes a clear tone when tapped works well. One has to tune the system to the stemware's resonant frequency. This can be done several different ways. My favorite way is to start with the speaker at a very low amplitude, box open, and the stemware taped firmly in place on the brick. Rapidly tap the glass with a tuning fork mallet as you adjust the function generator, 10 Hertz at a time, listening for the beats to go away (much like tuning a piano). This has to be done in the box with the stemware firmly taped to the brick. The stemware's natural resonant frequency shifts lower once its base is firmly taped to the brick. The stemware is mounted this way so that at high amplitude the glass doesn't vibrate around and generate harmonics, thus losing energy.

Once tuned, write down the frequency. Make sure the paper feather is in place and curved outward. Zero the sound level meter and place it in the box. Close the front cover and secure it in place. Now the volume or amplitude can be increased somewhat, to see how well the feather vibrates. Readjust the frequency of the function generator to achieve the resonant frequency of the glass, by ear and/or by one hertz intervals. Watch the feather vibrate. Once resonance is achieved, the paper feather will vibrate violently. You should be set. Turn up the volume on the audio amplifier, ie the amplitude, and the glass should shatter. Fine adjustments of the function generator at high amplitude may be needed to maximize the resonant amplitude of the glass.

Optional: Setup a strobe light with a second function generator. Adjust the frequency fast enough to slow the motion of the feather and glass rim. Do this when the speaker is at low volume.

Speaker/Horn Information:

The Speaker is an 8 Ohm D-408Ti 2" Titanium Horn Driver 4-Bolt, by Selenium Loudspeaker and was $222.00. The horn is a Selenium HL14-50 2" Exponential Horn 45x45 4-Bolt and was $27.00. Extra diaphragms are Selenium RPD-4400Ti Diaphragm For D-408Ti & D-4400Ti horn drivers and are $76.00 each. The Speaker total weight is about 21.25 lbs. The Magnet is about 7" x 1".

Videos of Breaking Glass with Voice

1. http://www.youtube.com/watch?v=amuPoPkAlx8&feature=player_embedded

2. http://www.youtube.com/watch?v=sH7XSX10QkM&feature=related

3. [http://www.youtube.com/watch?v=O9FrMkhQoA4 Myth Busters 1/3]

4. [http://www.youtube.com/watch?v=nHSGd2X1nc8&feature=related Myth Busters 2/3]

5. [http://www.youtube.com/watch?v=oXV45t6wlWU&feature=related Myth Busters 3/3]

References:

1. None

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