[CAUT] More on Single String Beats

[RicB]

Hi Wim

Variances in string diameter definitely can be a part of the picture.  
They are the other side of the coin as it were relative to the strings 
termination. Jim Ellis has some interesting things to say along these 
lines and perhaps he might voice a few of his thoughts on the matter. 
But as I understand it, variances in diameter at or very close to one of 
the terminations in the string itself can cause the string to vibrate at 
slightly offset frequencies in one or more vibrational plane. Just how 
this works and what the mechanisms involved are have not drawn my 
attention enough yet for me to quite feel sure about them, but I think 
we are in a different arena then the terminations massy vs. springy 
condition.

As far as this last bit goes. Askenfelt says outright that single string 
beats must be seen in the perspective of the termination as a whole... 
and goes so far as to include the soundboard area at the termination as 
part of this picture... a point I had not considered much yet, but when 
one stops to think about it it makes perfect sense.  There is so much 
micro movement going on between the bridge / bridge pins / bridge 
interface with the soundboard that is on a scale large enough to 
contribute directly to a single string beat condition that it is 
actually quite surprising the loose pin explanation got started in the 
first place... let alone gained so much steam. The point is that any 
movement of the termination in phase with any particular vibrational 
direction and frequency, regardless of what the root cause of that 
movement is, will lead to a single string beat if that same in phase 
motion is absent or significantly different for any other vibrational 
direction at that same frequency.

I have an experiment going that more or less torpedoes the loose pin 
thingy once and for all.  Anyone can do this very easily and quickly.  
Take two center pins and cut them to a length just longer then the width 
of the a typical upper treble unison... say A6.  Loosen the strings and 
put the center pins under them so that the they are 2-3 mm recessed from 
the bridge pins. Then bring tension up.  Do this say... 20 times over a 
whatever convenient period of time on different instruments you have at 
your disposal... and count how many times a false beat develops either 
right away or after a day or so.  You have done two things by inserting 
the center pins under the string.. You have created (simulated) a 
grossly exaggerated recessed notch edge and you've raised the string up 
the pin so as to allow for way more flag poling of the bridge pin then 
any common 20 year old bridge pin hole could ever dream of allowing for. 
Essentially, you'd have free floated the pins support 1 + mm below the 
strings contact with the bridge pin.  Now... if loose pins were anything 
even remotely close to a <<cause>>... you will find a very high 
percentage of single string beats resulting from the experiment. But 
this doesn't happen. Only small percentage will do so.  In fact... you 
can actually alleviate some single string beats this way. 

I got an interesting off line note from a fellow whose starting a series 
of experiments about falseness in general after the first posting, which 
I am sure all will find interesting when its completed.  There is an 
assumption that some of the falseness we hear (and I am not refering to 
inharmonicity per se') actually contributes pleasurably to piano sound. 
I probably will go a ways down that road of reasoning... but only to a 
point.  And personally... when it comes to what are actually and 
undeniably single string beats... I find nothing attractive or 
pleasurable about them at all.  Quite the opposite really.

Cheers
RicB


    There is one thing that Ric mentioned that gives me reason to believe
    the reason there are "false" beats is because of the differences of
    the diameter in the string itself. He said "the addition of mass to
    the strings front bridge pin, or an area very close to same has an
    impact on the speed of the beat.... and at some optimal degree of mass
    addition (or even > subtraction perhaps) the beat disappears."

    When strings are drawn to size, it goes through smaller and smaller
    holes. The strings are pulled by an electric motor. As with any
    electric device, the speed of the motor changes as the amount of power
    fluctuates. The surges in power are effected by other electric
    appliance starting or stopping.

    My theory is that in the factory where string is made, there are
    lots of large electric motors that stop and start constantly. It
    doesn't take much to cause a small surge in any of the motors. As the
    surge occurs, it slows down the speed in which the wire goes through
    the hole. This, in turn, changes the diameter of the string. It might
    be so small that it is undetectable, but it might be enough to cause
    the string to change it's beating pattern.

    Am I way out of it, or is this a plausible cause of false bats?

    Wim
    Willem Blees, RPT
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