[CAUT] Accujust and grunting fish bait

[Fred Sturm]

On May 9, 2009, at 8:22 PM, Fred Sturm wrote:

>  the original topic, which had to do with the theory that string  
> vibrations could be coupled, through accujust hitchpins, to the  
> plate, and could make the plate vibrate/resonate in some way. If we  
> want to try to see if the analogy between a stake driven into the  
> earth, abraded by a hoe, and a string terminated on a vertical pin,  
> driven into a hole in a mass of cast iron, has any validity

	Returning to the original topic, and analyzing it by the model of a  
driver and a membrane/resonator:
	With a soundboard, the string is the driver, and it is firmly coupled  
to the SB assembly via bridge pins. The speaking length of a struck  
string has quite a bit of energy, and it is driving a relatively light  
weight material, selected for its capacity to vibrate (a lot better  
than many other woods, for instance).
	The vibration of the backscale of the strings is very low in energy,  
relying entirely on what is fed to it in the way of "sympathetic"  
vibrations (mostly the bridge conveying energy back from the SB to the  
back length). The accujust pin is not a firm coupler, in that the  
string loops around it, and pivots at the loop when it vibrates. Very  
little of the vibrational energy of the string is transferred to the  
pin. The plate is very massive, and not a good resonator (you can make  
it ring if you hit it with a hammer, but it takes a lot of energy to  
get a significant amount of sound).
	The analogy with the stake driven into the earth, and rubbing the top  
of the stake with the hoe? Based on what I gather from Jeff's  
description, a lot of energy is being expended at the top of the stake  
(compared to very little at an accujust pin). The stake is somewhat  
flexible itself, and can be "set vibrating" and those vibrations are  
conveyed into the earth. The earth is pliant, so the stake can  
"vibrate within it" and create waves which are analogous to  
soundwaves. (The accujust pin is set into a material that is not at  
all pliant, and the pin will be hard pressed to vibrate within the  
plate hole). Based on Jeff's description, there is a sound produced in  
the air, though whether or not it is related to the vibration in the  
earth is subject to doubt (at least on my part). I suspect the sound  
heard by the "grunter" is produced by the hoe head and the stake,  
moving air, not by the earth moving air. So the sound change from  
different heights of stake may have more to do with the portion of the  
stake vibrating above the earth rather than within it, or so I would  
picture it (though I guess the vibrational modes would be related in  
some way). All told, I find it difficult to draw a close parallel  
between this stake and hoe arrangement and a back length of string and  
accujust pin arrangement.
	In short, looking at this analogy, it seems a pretty big stretch. It  
seems very far fetched to believe that a significant amount of energy  
is conveyed into the plate by the backlength via the accujust pin,  
certainly not enough to make that massive plate resonate. At least  
that is my take.
	A way of investigating further: strike, pluck, bow, or otherwise  
activate the back length of the strings, and see what the result is.  
You will be introducing far more energy into that system than is  
introduced by playing the piano. Can you make the plate resonate?
Regards,
Fred Sturm
University of New Mexico
fssturm at unm.edu