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

joe leone <3n037@xxxxxxxxxxx> · Tue, 9 Mar 2010 20:32:04 -0500

On Mar 9, 2010, at 7:55 PM, Vern wrote:

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.

But, but but, a filet is usually an ADDED feature. My explanation  
decrees a rounded cut into SOLID material. And (oh, btw) I know more  
than Wikipedia anyway. lolol

Please explain what you mean by "transfer sonic waves....sonics...."?

Sonics, phonics, potato potata, tomato tomata.
 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?

Sine waves. Source of information? Me. Take a 6' 3 3/4" (1 meter)  
long piece of wood wand 3/4" x 3/4" (18.81x18.81mm) in cross section.  
Leave 20cm full sized and then mill the rest down to  
1/2" (12.54x18.81mm) ON the flat. Now holding the 20cm part, begin to  
whip this completed wand up and down casing it to whip/flex in an  
undulating fashion. It will fracture at the juncture of where you  
thinned out the wand.  .

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?

No, continued flexing. Everything has a finite number of cycles of  
life in it. Even me. How unfortunate for everyone. :)
Jo-Jo  (I don ha to cho ju any steenkin badges)

Vern