Can an opera singer really break glass or panes of glass with his voice?
In principle, Yes, an opera singer can break the glass. Every object can get into resonance and in extreme cases, it even breaks, if it is made to vibrate with one of its natural frequencies. This phenomenon is also known as the resonance catastrophe. A well-known example is a troop of soldiers who march in lockstep across a bridge and can bring it to collapse.
In the case of wine or window glasses, this can basically be done by airborne noise. However, the frequency must be hit precisely, maintained long enough and the stimulation is strong enough that sufficient energy is introduced into the glass. In this case, the vibration can build up in such a way that the glass eventually shatters.
But that’s just theory. In experiments, however, scientists cannot confirm that the human voice can do this at a greater distance. In experiments, singers have tried to break various types of commercially available glasses from a distance of about half a meter with their voice, under controlled conditions. In the voice tests, the singers even meet the natural frequency of the respective glass and were able to hold it for a long time. However, the glasses didn’t break.
Only with an artificial sound with amplifiers and horn loudspeakers of more than 130 dB, the glasses break. After all, the singer managed to achieve 110 dB (A) with their voice. However, this was less than a hundredth of the acoustic output that would have been necessary to destroy a glass of the type used. It would be conceivable, however, that glasses with slight previous damage in the material could break through the action of the human voice at a distance.
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There are videos on the Internet that show how people actually chop up glasses. The actors hold the glasses very close to their mouths. It could be that the glass is made to vibrate and finally to burst, not by the sound, but by the modulated airflow in the mouth. Some singers can help themselves with an object in their glass, others have chosen particularly easily breakable glasses.