What causes strings to go false?

February 8, 2012 7:01 AM

What causes strings to go false?

I was having a conversation with a friend of mine yesterday (he's a guitarist and I'm a cellist) about changing the strings on stringed instruments and when it was necessary to do so. Since I'm still a student, I don't change my strings as often as I need to, but I told my guitarist friend that I usually change them when I notice that they are going false (and they tend to have been false for quite some time before I get around to switching them out). This led to a discussion on the perception of pitch of false strings and whether or not the pitch is actually changing.

Here's what I know:

The string stretches as it's used, eventually causing the pitch to go "false" (ie. when the string is, in my case, bowed, the pitch will change when the bow comes away from the string - the ringing will be higher or lower than the intended pitch).

This explanation wasn't satisfactory to my guitarist friend. He wants to know why stretched strings are more difficult to tune, and I don't know what to tell him. Is there some science behind this that I don't understand?

posted by estherhaza to Media & Arts (7 answers total)

Best answer: Strings make noise, when plucked or strummed, because the tension they're under provides a certain amount of elasticity, i.e. their physical characteristics are such that they return to their initial state after a force is applied to them.

But in the context of musical instruments, we're not just looking for elasticity generally. We're looking for a very finely calibrated elasticity, such that the string, when plucked or strummed, will vibrate at a particular frequency before coming to rest.

Well, the strings on an instrument are under constant tension, and all that stress slowly degrades the material. As strings age, the the physical properties of the material change so such that the variables in the elasticity equations are different. Again, they're still elastic, but keeping them at that precise value of elasticity gets harder and harder.

Eventually, a string will wear out to the point that it ceases to become elastic at all--it becomes plastic, i.e. it undergoes a permanent physical deformation when force is applied, i.e. it breaks.

Or, at least, that's how I understand it. I'm sure someone around here can provide a more precise explanation.
posted by valkyryn at 7:09 AM on February 8, 2012

The string stretches as it's used,

Which results over a very long period of time in something called metal fatigue. An extreme example is repeatedly bending a paper clip until it breaks. The effect on a vibrating guitar string is much less pronounced, but basically the same physical mechanism: the metal becomes increasingly brittle - i.e., less flexible - with time.

Guitar strings are usually made out of stainless steel because it is durable and rust resistant - but not impervious to the effects of oxygen and other chemicals. Stainless steel is also naturally a bit brittle. So when you combine the mechanical wear and tear with the environmental exposure, the physical characteristics of the metal change over time and hence the sound of the string.

Or it could be you just need more practice.
posted by three blind mice at 7:20 AM on February 8, 2012

When they're under tension, they're always getting deformed to some extent; they're not perfectly elastic, and this deformation leads to them going out of pitch. But the rate of deformation varies over time. During the string's useful lifetime, this deformation is gradual. But once the elastic limit is reached, the deformation accelerates rapidly.
posted by Hither at 8:11 AM on February 8, 2012

I've noticed that excessive corrosion and/or grunge can cause adverse effects on playability and tuning anomalies. I guess these conditions cause strings to exhibit uneven density, causing some odd behavior, compared with new strings which are generally uniform along the entire length. Another possible effect is physical deformity in the string, which sometimes occurs where a string is plucked and/or where strings get pressed against frets. I'm not sure how such a problem might get exhibited on an instrument like cello, which tends to be plucked and stopped with much less vigor.

New strings often have a very vibrant sound when first strung up, but that elasticity is very short lived as strings settle into their tuned up tension. Whatever the case, as the longer I've been playing, the less often I find the need to change strings. Strings going "false", or more often, going "dead" just seems to be a pretty rare thing for me. Strings just seem to last a pretty long time for me.
posted by 2N2222 at 8:17 AM on February 8, 2012

Note: the OP said, "I'm a cellist."
I don't think stainless steel applies here, does it?
posted by exphysicist345 at 12:24 PM on February 8, 2012

The timbre of a string comes from all of the upper harmonics, not the fundamental. i.e., if you play a 440Hz A, the fundamental is 440 Hz but the timbre comes from all the frequencies that are multiples of 440 Hz. When a string is nice and new and clean, you get a whole lot of these, but as the string gets old and dirty, it kills the upper harmonics and can introduce some nasty new ones.

Moreover, the intonation of a fretted instrument will change as the strings age. So if your guitar is set up to play perfectly in tune at the 12th fret when the strings are new, when the strings age, it will be playing slightly out of tune. This is also the case for fretless instruments but it's much easier to adjust on the fly I would imagine, but shifting your finger slightly.
posted by unSane at 12:56 PM on February 8, 2012

As unSane said, any wound string will get dirt, oil, dust, skin cells, etc between the winds of the outer wire. This hampers the vibration. That, and metal fatigue.
posted by Danf at 1:12 PM on February 8, 2012