Can a soprano shatter someone's spectacles by singing a loud, high note?

Discussion in 'Music Talk' started by alpha1, Oct 30, 2006.

  1. alpha1

    alpha1 I BLUES!

    http://www.phys.unsw.edu.au/~jw/musFAQ.html#shatter

    The answer is no, but the question is not as bizarre as it sounds. Consider the phenomenon of resonance. Some systems, such as a child on a swing or a wine glass, can vibrate and store energy of vibration at a particular frequency, their resonant frequency. I give my nephew on the swing a gentle push, then another, then another... after 20 pushes he is flying three metres in the air, which is far higher than I can throw him. The energy of all the successive pushes has been stored in the vibration.

    Some wine glasses can ring spectacularly at a particular frequency: give them a flick and a nearly pure sine wave sounds. Suppose that the singer sings this frequency (it falls in the soprano range, and operatic sopranos are good at concentrating lots of energy in the fundamental frequency). A little sound energy gets stored in the glass with each vibration cycle and eventually a substantial amount of energy is stored in the glass, causing oscillations of large amplitude.

    If you use very high acoustic power from an amplifier and loudspeaker in a confined space, it is possible to break a wine glass. This is described by W.C. Walker in "The Physics Teacher", 1977 (Vol 15, pp. 294-296). A manufacturer of recording media once used a film clip of a glass being broken by highly amplified sound in an advertisement, and this may be the origin of the now widespread comic cliche of glass breaking when a singer sings.

    Can a singer shatter a wine glass this way? I doubt it. The power output of a singer is less than 1 Watt. Of this, only a tiny fraction impinges on a wine glass in the auditorium, and, in most situations, the geometry is such that the wine glass is not strongly coupled to the sound wave. Further, the wine glass can lose energy both internally and by re-radiation, or just rattling. In any wine glasses I have touched, the resonance is just not that good. Mind you, I don't mix with the class that has really fine glassware!

    Late news. I was tipped off that a wine glass was shattered by an unamplified singer in a session of Mythbusters TV show. I've not seen the show, but the transcript suggests that the glass was held very close to the singer's mouth. This geometry could couple a substantial fraction of the singer's power into the glass. So don't expect it to happen under normal voice - wine glass geometries! ​

    As for spectacles, they hardly ring at all: the frames and attachments are too good at removing energy. Find a pair, give them a flick and see.

    However, resonance can do some much more spectacular things. A bridge constructed across Tacoma Narrows, Washington, had strong resonances. In November 1940, the wind excited these resonances so strongly that the bridge fell. The film of the event is shown to first year physics and engineering students around the world
     
  2. alpha1

    alpha1 I BLUES!

    I guess that sums up.

    Singers shattering glass is nothing but loads of Baloney!
     
  3. vedder

    vedder New Member

  4. alpha1

    alpha1 I BLUES!

    He used amplification :-|
    and he cannot sing that high too.
    double :-|
     

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