It was mentioned in this column that Cecil could not find an example of a glass being shattered with an un-amplified human voice. This was actually accomplished on an episode of MythBusters.
Note that the column, Can opera singers shatter glass with their high notes? is a Straight Dope Classic and was originally published on May 11, 1990, almost 15 years to the day before the Mythbusters episode of May 18, 2005 aired.
Also, Cecil never said it was impossible. He did note that it was highly plausible that a trained singer could match a glass’s resonant frequency with the unamplified human voice and shatter it.
OK. My intent was not to correct, only to provide info that could be used to update the column.