Re: [Harp-L] Re: Yellow Brass (was GM)

[Vern <jevern@xxxxxxx>]

On Mar 9, 2010, at 3:19 PM, joe leone wrote:
> 
> Leaving a sharp step in the rivet boss to reed shaft causes vibrations in the reed to transfer sonic waves to the sharp inside corner (where the reed is weak). Constant sonics at that point has the effect of singing high notes at a shell blown champagne glass, It can cause a fracture.
> 
> smokey joe  

The simpler explanation is that any abrupt change in cross section causes a stress concentration.  Wikipedia sez: "Geometric discontinuities cause an object to experience a local increase in the intensity of a stress field." A fillet at the base of the reed reduces the abruptness of the change in cross section and reduces the local stress.  

Please explain what you mean by "transfer sonic waves....sonics...."?  To what kind of waves do you refer, compressive waves or some kind of higher-frequency mode of transverse vibration? How do you know that such waves exist in harmonica reeds?  What is your source of this information?  

To fracture a glass, you must sing to it very loudly at its natural frequency of vibration.  Are you referring to vibration at frequencies other than the reed's musical pitch? 

Vern