Inharmonicity (bowed strings)

[Susan Kline]

At 07:50 AM 8/16/98 -0400, Rob wrote:
>Hi Jim,
>
>I didn't want to take up everybody's time with this, but when you said:
>
>>>  My violin strings do exhibit a strange phenomenon in that the
>>fundamental of a bowed string gives a higher pitch that the same plucked
>>string (drives me bananas).<<
>
>I thought perhaps this is what's happening with my viola (to which I am a
>relative newcomer).  I also seem to be able to hear a pitch difference
>between the A & D strings that varys between upbows and downbows - it will
>sound in tune one minute, and out, the next.
>
>Any comments would be appreciated.  Thanks.
>
>Rob Stuart-Vail
>

I'll be interested to hear Jim's comments, too. 

However, as a cellist perhaps I can shed a little light. When you bow a
string, there are tiny teeth on the hair which, made sticky by rosin, grab
the string and pull it sideways. There is also the obvious pressing
downwards on the string in order to get enough friction to pull it
sideways, but it's the sideways pull that sets it in motion. 

Sometimes picturing this can greatly improve one's tone. The pressure can
be adjusted, along with the distance from the bridge, so that it is _just_
enough to pull the string. The need to avoid clutching the bow, and the
importance of the smoothness and straightness of the stroke are obvious
when you think of pulling exactly to the side, allowing the string the
maximum freedom. However, a smooth bow change must allow the bow to stay in
motion, or else the hair will damp the string like a blocking piano hammer;
therefore, picturing a very, very slender ellipse for the bow change helps
keep the tone ringing during the change in direction. If the bow is lifted
off in a curve, the note is more free to ring after it is removed. 

So, the drop in pitch as the bow is taken off results from no longer
pulling the string to the side, and no longer pressing it downwards.

The difference between upbows and downbows should be controllable with more
experience, sort of like differences in intonation when using different
fingerings. It all becomes automatic ... have faith.

There is also a big change in pitch from playing very loudly vs. softer.
The tension of the string is so low that the excursion (right word?) in the
middle of the loop is quite wide, which by raising the tension also raises
the pitch. No doubt this happens in pianos, too, but the higher tension and
stiffness keeps us from hearing it.

(Dr. C. --- why is this?)

Regards,

Susan


Susan Kline
P.O. Box 1651
Philomath, OR 97370
skline@proaxis.com