dick g -

By way of explanation:

The normal "action" of a string results when you pull it sideways and let go, or in the case of a fiddle you rub it sideways for a succession of sideward motions of the string. This transverse vibration happens at a particular frequency, so you get a particular pitch.

In the recommended "twist the string" mode, if the string is not perfectly round, bowing will cause the twist to wind and unwind. Since the string is much less stiff for torsional winding/unwinding, the frequency at which it vibrates in "torsional mode" will be significantly lower. The "evidence" suggests that it's on the order of a "part of an octave" lower than the normal transverse vibration mode, so you can tune it to a fifth lower than normal transverse pitch for that string.

There is also a third vibration mode for a string that can sometimes be excited by "stroking it lengthwise." This "longitudinal mode" of vibration is usually very much higher in pitch than the normal lateral mode. For guitar strings it's often something like 6 times the frequency of the normal lateral mode vibration. Exciting of the longitudinal mode of vibration most likely accounts for some of the more piercing squeaks one hears from beginning fiddlers, and probably is a component of the "fret noise" squeaks often heard from guitars.

The "longitudinal mode" is about right for musical sounds if one ties about 40 to 60 feet of binder twine to a barn door, leans back hard on the end of the string, and whips it with a hoe handle. (This instrument is documented in some "found instrument books.")

It all depends on which direction the string is going when the motion hits the bridge, but really results from the different string stiffness when you stretch lengtwise, pull sideways, or twist in a winding motion.

John