Legend has it that the famed opera singer Caruso had a voice that could shatter glass. The probable truth of this legend.
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                      Earth & Sky                        Sunday, August 22, 1999

                      DB: This is Earth and Sky. A listener wants to know, "Can
                      people actually shatter glass by singing a particular
                      note?"

                      JB: To understand the answer to this, you need to know
                      that every object has a resonant frequency -- that's the
                      natural frequency at which an object vibrates. If you run
                      a damp finger along the rim of a glass, you might hear a
                      faint, ghostly hum -- the resonant frequency of the glass.
                      To shatter the glass, the singer's voice has to be able to
                      match that frequency.

                      DB: Also, the singer has to sing very loudly. A jackhammer
                      operates at a loudness of about 90 decibels. The human
                      threshold for pain comes at about 120 decibels. To shatter
                      a glass, a singer has to produce a note with an
                      ear-splitting intensity of at least 135 decibels.

                      JB: And the singer also needs to hold that note for at
                      least two to three seconds -- for the vibration to build
                      up enough to cause the glass to shatter. It helps to have
                      the right kind of glass -- a large one -- with thin,
                      nearly vertical sides. In the late '70s, laboratory
                      experiments with a professional soprano and a trumpet
                      player showed that neither could shatter glass. The famed
                      tenor singer, Enrico Caruso, was said to be able to do it
                      -- but his wife denied it. So there are physical
                      conditions under which a human voice should be able to
                      break a glass. But it's improbable that an unamplified
                      human voice could actually do it. With thanks to the
                      National Science Foundation, we're Block and Byrd for
                      Earth and Sky.
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                      Author(s): Marc Airhart

                           Saturday August 21, 1999 | Monday August 23, 1999