Yow-yow-yowing bass strings

[Carl Meyer]

Here's another wild guess.  Just what you wanted Huh?

The swage at the ends of the winding, if it is horizontal, will be stiffer in the horizontal and less so vertical.  Now if the string were installed with the swage vertical at one end and horizontal on the other the effect would cancel.  Hence, no more Yowing.  If they were oriented the same it should be worse.

David Sanderson swages his core wire triangular so that the stiffness will be the same in all directions.  It's my understanding that it was done to prevent bichords from having different stiffness in the two strings if they were oriented different.  Could this be significant for single strings?
Although I haven't used his strings, I'm impressed with the concept.  I believe it is patented.

To check longitudinal stuff try the rub test or scratch test.  Starting at note one rub or scratch the winding and listen for a high harmonic of  about three octaves and fifth.  That should progress smoothly up the scale.  I've seen some go up and then down, and then go up again.  Interesting!

Carl Meyer  Assoc. PTG
Santa Clara, California
cmpiano@attbi.com   
 


----- Original Message ----- 
From: "Robert Scott" <rscott@wwnet.net>
To: "Pianotech" <pianotech@ptg.org>
Sent: Friday, January 24, 2003 10:38 AM
Subject: Re: Yow-yow-yowing bass strings


> 
> Here is my guess.  The Yow-yow-yowing is a false beat at a high 
> partial.  As the partial goes through its false beat, the apparent balance 
> between the partials seems to change, thus giving the impression of 
> changing voicing, or yow-yow-yow.
> 
> So what can cause a false beat at a high partial?  I suspect that it is a 
> difference between vertical inharmonicity and horizontal 
> inharmonicity.  Remember that inharmonicity is caused by the stiffness of 
> the string - its resistance to bending.  But suppose that a string has more 
> resistance to bending in, say, the vertical direction than it does in the 
> horizontal direction?  Now recall that when a string is struck, it begins 
> precessing into an oval-shaped pattern, moving in both the up/down 
> direction and in the side-to-side direction.  If the string has a different 
> amount of stiffness depending on the direction of bending, then the effect 
> of inharmonicity will produce a different resonant frequency in each of 
> these directions.  That causes the string to vibrate at a slightly 
> different rate up and down than it does side to side.  These two rates of 
> vibration occur simultaneously and beat against each other, giving the 
> Yow-yow-yowing.
> 
> Let's speculate even further about what might cause a difference in 
> stiffness in the horizontal and the vertical bending direction - especially 
> in bass strings.  Some bass strings are wound on hexagonal cores.  If the 
> machine that makes the hexagonal core is imperfect, then the hexagon might 
> come out flattened a little in one direction.  That would certainly make it 
> easier to bend in the flat direction and harder to bend in the 
> perpendicular direction, which would lead to yow-yow-yowing.  And even if 
> the core is just a round string, it may be that somewhere in the winding 
> machine, the core string goes over a hard surface that crushes the 
> cross-section a little, making it oval instead of round.  That, too, would 
> lead to a difference in stiffness that depends on the direction of 
> bending.  Finally there is the copper winding itself.  It contributes only 
> a little to the overall stiffness of the bass string, but it does 
> contribute some.  Suppose the winding machine were mis-adjusted so that the 
> copper wrappings were pressed tightly against each other on two opposing 
> sides of the cross-section, but were a little less tight in the directions 
> that are perpendicular to the tight directions.  This could give the 
> completed string a difference in stiffness in one direction vs another.  So 
> my guess is that it is the fault of the machine that makes the bass strings.
> 
> -Bob Scott
>   Ypsilanti, Michigan
> 
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