Re: [Harp-L] Re: The Comb Debate

[Vern <jevern@xxxxxxx>]

On Sep 6, 2010, at 4:48 PM, joe leone wrote:

> Tonight I was inside a Bb spl-20 and doing my special tuning, but I was having trouble getting the #9 just right.
> I had to walk the reed sideways to do some adjusting and when I re-centered the reed, something happened
> that ALWAYS happens when I do this. The volume and 'carry' of the reed decayed a bit. To get the reed back
> to snuff, it was necessary to tap the rivet in my die set to REseat the rivets wedge/friction/jam fit. To tighten it
> in other words.
> 
> Then the reed sounded right. This is why vibrations play a VERY important part in harmonica integrity. The loose
> reed wasn't imparting it's natural sonic waves TO the reed plate.

Your treatment worked for the symptoms you encountered but I submit that your diagnosis is wrong.   A loose reed can rattle against the reedplate.  These collisions convert the mechanical energy of vibration into heat.  Thus damped, the reed acts a bit balky and dull.  You characterize this as lack of "carry".   When you tightened the rivet, the rattle stopped and the reed behaved normally.  

You can demonstrate this with a dinner knife while sitting at the table.  Hold about two inches of the blade tip firmly against the top of the table with the knife protruding away from the edge.  Tweak the handle and observe the vibration.  Now loosen your grip so that the tip of the blade can rattle.  The vibration dies much more quickly.  

This effect is (or was...I worked for GE in the '50's) used to suppress vibration in the long compressor blades of jet aircraft engines.  Each blade has a projection that reaches out to just touch similar projections from neighboring blades.  When a blade starts to vibrate, the collisions of the projections absorb the energy.  Some blades also have loose metal collars around their base that rattle and absorb vibration. When some jet engines wind down, you could hear all of these loose parts rattling on the last turn of the rotor. In some engines the blades were deliberately loosely connected to their hub to suppress vibration. 

>  I therefore submit (for ya'all's critique) that all the parts have to fit right for the harmonica to play right.

I cannot argue with your final conclusion!
> 
Vern
>