Re: [Harp-L] SPAH 2010 Comb Test: a thought experiment (long)

[Michelle LeFree <mlefree@xxxxxxxxxxxxxxxxxxxxxx>]

 Vern writes:
> On Sep 2, 2010, at 7:34 PM, Michelle LeFree wrote:
> > >  
> > >  ...............I fully realize that this idea is in conflict with Vern's long-standing position. His argument that the wavelength of the sound a harmonica produces are much longer than the dimensions of a reed chamber and therefore the comb material can have no effect on the transmitted sound seems to hold water.
> My argument about the size of the chambers was to refute the notion that the air in the chambers could form a resonant cavity or column.

Yes, I recall. I'm saying that there are other issues at play here.

> > >  Yet, how can this clear difference in how harps vibrate in the player's hands and mouth ~not~ bear some sort of a relationship with the sound emitted out the back of the harp?
> Only for the sake of argument, let us assume that the combs of different materials vibrate more or less.  Their exposed area thus acts as a loudspeaker.  However, the very small area of the exposed surfaces and the small amplitude of the vibration produce a weak sound that is masked by the far louder sound of the modulated airstream.  This is like starlight in the daytime.  We all know it is there but it is masked by sunlight.

Nah, I'm not saying that the sound emitted from the harp has a 
"loudspeaker" effect. I'm saying that the fact that one harp vibrates 
more in the hand than another must have some kind effect on their 
emitted sound.

There is a fixed amount of acoustic energy produced by the chopped air 
flow caused by the vibrating reed. I'm contending that the reed, since 
it is mechanically attached, transmits some of that energy to the entire 
body of the harp and that energy is manifested as a vibration -- that 
the player can feel.  Moreover that the acoustical properties of the 
materials from which the harps are constructed cause a difference in the 
amount of energy transmitted to and through the body of the harps. And 
the differential amounts (and frequencies) of energy absorbed by the two 
harps must have an impact on the sound that then flows out the back of 
the instrument. Further, I say that since the combs are the only 
difference in the materials the two (hypothetical) harps are made of 
that the comb material is what causes these differences in the 
vibrations transmitted to the player and thence the sound exiting the 
instrument. I'm just applying the laws of conservation of energy (i.e., 
the 2nd law of Thermodynamics).

Whew! :-)

> If you tried to design a structure that would resist vibration, you could hardly do better than to laminate layers of material of different acoustic impedances, (air, wood, brass) then filligree them with a lacework of openings.  All of these boundaries cause internal reflections that bounce the sound back and forth between the interfaces to be absorbed without ever reaching the outside.

You seem to be reinforcing my point here, old pal. ;-)

> If this were a perceptible effect and part of the harmonica playing experience, some of the six players would have felt the differences...or lack thereof in the brass comb repeats.

OK, as to the players feeling vibrations in this test, what about that 
huge ballast weight (the section of metal rod you intelligently added to 
your jig to prevent the players from detecting any weight differences in 
the combs)? That weighed significantly more than the harps and surely 
would have dampened any vibrations the players might have felt. Plus, 
the players were instructed not to hold the harp/ballast jig in a way 
that might block the sound exiting the back of the instrument, so they 
weren't really in a position to feel the harp itself. Finally, so far as 
I am aware, no one ever mentioned anything about the harp vibrating in 
the entire course of the experiment so far as I'm aware. It wasn't a 
question asked of the players and to my awareness the topic never came 
up. In fact, I don't think it came up on this it until Smokey Joe 
mentioned it. I just happened to have been thinking about it and 
recently came to the realization that the way harps vibrate differently 
in the hand can shed a new light on the comb experiment.

I'm just trying to introduce a different way of thinking about the 
acoustics of playing a harmonica. I don't recall anyone ever taking my 
approach to analyzing the energy transmitted to the body of the 
harmonica as manifested by the amount of vibration the player feels in 
the hand and mouth. It's hard to argue with the fact that energy felt by 
the player is energy that didn't go out the back of the harmonica. And 
that implies that the acoustical properties of the components of the 
instrument ~must~ have an effect on the sound exiting the harp.

Thanks for your input here, Vern.

Michelle