The renowned soprano Dame Nellie Melba is reputed to have performed this trick and in 1971 the audio-tape maker Memorex based a very successful advertising campaign around Ella Fitzgerald shattering glass both when singing live and when recorded on its tape cassettes (a claim the company still stands by today).
Even so, it is hard to believe that mere vibrating air can shatter solid glass. The explanation lies in the simple yet extraordinarily powerful phenomenon of resonance, according to which even relatively weak vibrations can perform miracles, if tuned to the right frequency. A classic example is the playground swing: even a small child can propel an adult many feet up in the air by pushing at the right moment. In the case of a wine glass, the trick lies in using fine crystal glass, (which has a relatively rigid molecular structure) tapping the glass to hear its natural ringing frequency and then hitting that note and sustaining it. If a singer’s voice is both stable and strong enough, it will set up resonant sound waves inside the rim of the glass that eventually shatter it.
All of which prompts one to wonder whether something similar might explain the Old Testament story about the walls of Jericho being brought down by the sound of horns and human voices. It seems unlikely: neither the nature nor the shape of walls are suitable for setting up the all-important resonance.
Sound consultant David Lubman of Westminster, California recently examined the possibility that the walls were flattened simply through raw noise. He calculated that to damage Jericho’s stone or mud-brick walls the acoustical power required would be almost a million times greater than even a generous estimate of the power produced by the horns and besieging army. This led him to suspect that the legend is a metaphorical reference to the psychological effect of the sound, which might have emboldened the army while putting the wind up the city’s defenders.
However given that everything has a resonant frequency it is possible.
So to answer the orginal question of whether Opera Singers Really Can Shatter Wine Glasses by Singing – it as a resounding ear shattering YES!