It’s the stuff of legend — and even of vintage TV commercials — but can an unamplified singer really break a glass using his or her voice alone?
The answer is yes, but it’s not easy.
In short, every piece of glass has a natural resonant frequency — that is, the speed at which it will vibrate given a particular stimulus, such as a sound wave — and wine glasses are especially resonant because of their hollow shape. (That’s also why they sound pleasant when they’re clinked.)
But here’s the secret: it’s not about singing a particular high note, like the legendary "high C." It’s about finding the same note as the glass’s natural resonant tone (also what you hear if you flick the glass with your fingers, or wet a finger and ring it around the rim), then singing loudly enough that the glass vibrates to the point where it will fail.
The key, though, is the glass itself: cheap wine glasses from the dollar store won’t cut it, because they don’t have the same resonance as crystal. It has to be the expensive kind.
Don’t try this at home, though, because you can hurt yourself. Just take our word for it — or watch the phenomenon in action in this video: