Mudcat Café message #1686933 The Mudcat Café TM
Thread #89392   Message #1686933
Posted By: JohnInKansas
06-Mar-06 - 10:34 PM
Thread Name: Difference in fiddle bows?
Subject: RE: Difference in fiddle bows?
Bert -

You have omitted a couple of very important things that you need in order to make your "technological bow."

While the weight of the bow is an important feature, to get the right "feel" it's necessary to get the right weight with the right center of gravity and with the proper longitudinal moment of inertia. The longitudinal moment (IL) determines how readily the bow follows pitching of the bow when you move from one string or another.

While one can achieve a particular weight, c.g. and IL value with a variety of longitudinal distributions of the weight along the length of the bow, violinists prefer a different effective IL when they play near the frog than when they play near the tip, and the preference doesn't appear to be linear with how far up or down the bow they are contacting the string. Thus the entire weight longitudinal weight/mass distribution is critical to making a bow with the right "feel."

The most obvious innovation with the Tourte bow is that the bow is necked down near the tip, and the principal "spring" under moderate pressure against the strings is by rotation of the tip via very localized bending at the tip, with little deflection along the length of the bow. For best feel, the spring constant is non-linear, by design, so that the tension in the hair changes very little for small deflections; but of course to allow the fortissimo, the spring rate has to increase fairly rapidly for larger deflections. When the tip rotates the direction of the hair tension is in a different direction relative to the tip and the "springy" part of the bow adjacent to it, so a different spring rate can be brought into effect by the detailed shaping of the "head" and the immediately adjacent shaft of the bow, without requiring a substantial deflection of the main shaft.

It is not sufficient to have the right weight. You have to also get the right IL.
It is not sufficent to get the right weight and IL, you have to get the right variation in effective IL with changes in the location at which the bow pivots on the string.
It is not sufficient to get the right deflection under load against the string. You have to also get the right change in the rate of deflection over a range of pressures of bow to string.

Then there's the lateral anisotropy to be considered but ...

And the hair tension has to be easily adjustable.

And the bow has to look nice.

John