General Question

PhiNotPi's avatar

Why do wine glasses emit static noise?

Asked by PhiNotPi (12185 points ) April 3rd, 2013

Yesterday, while I was holding by ear close to a wine glass (specifically the interior of the glass), I noticed that they produced sound. The noise sounded like static, was only apparent when I practically put my ear inside of the glass, and appeared to increase in volume when my TV was on.

What causes this mysterious sound? Was it Helmholtz resonance?

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6 Answers

Rarebear's avatar

Yup. Heimholtz resonance.

PhiNotPi's avatar

One other thing that I noticed was that the sound was lowest in pitch as my ear was closest to the glass.

Rarebear's avatar

@PhiNotPi That may be a function of the sound waves bouncing and resonating off your ear. No idea.

PhiNotPi's avatar

I was thinking that the airflow is constricted between my face and the wineglass. Helmholtz resonators, such as the ocarina, produce lower-frequency sounds as the area of the open holes decreases. In this case, the “hole” would be the space between my face and the glass.

PhiNotPi's avatar

It turns out that both @thorninmud and @Rarebear are correct. It’s a Helmholtz resonator that amplifies the ambient sound.

more info (this goes into the math of calculating the pitch, and explains all of my observations)

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