Sympatheti c Strings

Paul Erlich wrote:

>The cross-sectional area of a string is almost negligible compared with that
>of a tube or plate. Thus the string will receive almost no energy from
>incident sound waves, while a broader object can absorb significant amounts
>of energy.

The cross-sectional area of a string may be "almost negligible" but it
exists. I just performed some experiments on four stringed instruments
in my collection, a cheap violin, a sanxian, a small zheng and an
Appalachian mountain dulcimer. Of these, I got the best results from
the violin and the sanxian. On the violin, I got the best results on
the A and E strings, with the E string sounding louder. I don't have a
scientific way of measuring the guage, but it looks like the violin E
string is the thinnest of all the strings on all four instruments. It is
also unwound wire and tightly stretched. The timbre of the sympathetic
resonance is similar to the plucked string timbre.

The second best results came from the sanxian. The strings are longer
than those on the violin, and I think they're made from wound silk. They
look like they're just a little bit thicker than the G and D strings on
the violin. The timbre is similar to the plucked string timbre.

Both the violin and sanxian have excellent resonators, with the sanxian
having a small, round, snakeskin-covered box.

My small zheng (Chinese zither-type instrument) has thin wire strings
between the thickness of the A and E strings on the violin).
I didn't have time to find the tuning key right now to tighten them, so
they aren't really tightly stretched. The resonator is much bigger than
that for the violin - it's basically a wooden box that all the strings
are mounted on, with holes in the bottom. It worked better when I picked
the instrument up so that the sound could come out the small holes, but
the resonance still wasn't very loud. Maybe the large moveable bridges
don't transmit the sound as well to the soundboard.

The dulcimer has nylon strings slightly thinner than those on the
sanxian. I can't really account for why this one is not very loud.
Maybe metal strings work better than nylon? Maybe the resonator
doesn't amplify the sound very well?

I got these results by loudly singing the same pitch as the string is
tuned to, as close to the plucking area (and the string itself) as
possible. Singing a different pitch from the pitch of the string does
not give the effect, so it seems unlikely that the sympathetic vibration
comes from exciting the resonator. I think the original excitation
must be airborne, and the strings sound louder if they have good
resonators.

Lydia Ayers

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Lydia:

You wrote:

'' I don't get a sympathetic ringing at
the pitch if I hold all the strings (both sides of the bridge) so that
they cannot vibrate.''

I think you misunderstand this. The soundboard itself is here only a
transmitter - whose surface area is receiving the sound from the air. Try
the reverse of what you describe - hold the soundboard firmly (I assume you
haven't got an instrument from Cremona) so that it cannot vibrate. Sing
into the back of the violin. The sympathetic motion should be minimal.

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