[CAUT] Semantics - Resonance

[Ed Sutton]

O.K. 
Here is a simple and fun experiment to understand resonance through personal experience.
First, find a PVC pipe or any kind of tube, about 2 or 3 inches in diameter and maybe 6 feet long. 
Away fromm the tube, sing a long glissando. Start with the lowest note you can sing, and make like a slide whistle, up to the highest note you can sing.
Now try to do the same thing, singing into the tube.

The tube encloses a mass of air, which has a series of harmonic resonances (harmonic as in 1X, 2X, 3X, 4X, etc)
When you try to sing a glissando into the tube, the resonances will force you to sing the harmonic series of the tube's air mass.
It's a remarkable experience to feel your voice being "snapped" into pitches you are not trying to sing, and not being able to sing the pitches you are trying to sing.

The "wolf tone" of a violin is also a resonance. 

In a soundboard, resonance is not desirable.

Resonances in the diaphragm and horn of early acoustic phonographs caused similar distortions, significantly improved in later acoustic phonographs. An aluminum diaphragm is much less resonant than a mica diaphragm. The aluminum diaphragm moves passively at the frequencies the needle drives it, and gives a better reproduction than a mica diaphragm.

The acoustic phonograph is also a transducer. The diaphragm converts sound waves into wiggles at the tip of the needle, which cuts the groove. When the groove wiggles the needle, the diaphragm converts the wiggle into a sound wave. The wiggle itself is silent. Waving a needle back and forth 440 times a second won't make a sound.

Ed Sutton 
  ----- Original Message ----- 
  From: Richard Adkins 
  To: Caut 
  Sent: Monday, May 18, 2009 10:15 AM
  Subject: Re: [CAUT] Semantics


  Not to continue a very very long and over winded discourse, but I read this last week.

  From the Baldwin Piano Co. website:

       "Meticulously constructed and tapered, Baldwin soundboards amplify the string energy to produce a rich, sustaining tone."

        I guess they don't know what they are talking about, according to you and they
        build the pianos. 

        Oh, and where does resonance come in to the equation? It seems to me the
        board is resonating to the frequencies set up by the energy imparted to
        the string under tension.

        Further enlightenment is required by our local gurus.

        Richard Adkins
        Coe College


       
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