The Sharpening Effect

By Marc Friedlander

 

Several decades ago, while playing a Prelude by S. L. Weiss, I noticed something so puzzling, it has periodically occupied my mind ever since.  To this day, I often ponder the peculiar event I observed - and continue to observe - whenever I play this particular Prelude, or any other piece that requires a tuning change. 

From here on, I’ll refer to the curious event I observed as the sharpening effect – the tendency of a nylon guitar string to go sharp (gain in pitch), shortly after drop tuning the string.  By drop tuning, I am referring to the common practice of lowering the pitch of a string to an alternate pitch.  There are many alternatives to the standard tuning of E-A-D-G-B-E.  The Weiss Prelude employs D tuning, which lowers the 6th string a full step.  For  “open G” tuning, you lower both the 6th and the 5th strings a full step.  Alternate tunings have been a common practice since the earliest days of the guitar’s predecessors, when Renaissance lutenists perhaps perceived the sharpening effect and pondered this anomaly.

            I apply the term “anomaly”, because by any logic, a string should never spontaneously get sharper, controlling for environmental variables such as temperature, humidity, and atmospheric pressure.   A guitar string is under tension (an axial load, pulling in opposite directions).  For a note to audibly gain in frequency (get sharper), it must either experience a decrease in scale length, a decrease in vibrating mass, or an increase in tension.  Since the scale length and the vibrating mass of a guitar string are fixed, an increase in pitch must be the result of an increase in tension.  The anomaly is that a higher tension also represents a higher energy state, in terms of mechanical potential energy.  It has been widely agreed by physicists for centuries that a closed system cannot spontaneously achieve a higher energy state. 

From Webster’s New World Dictionary:

en•tro•py

n.

1    a thermodynamic measure of the amount of energy unavailable for useful work in a system undergoing change

2        a measure of the degree of disorder in a substance or a system: entropy always increases and available energy diminishes in a closed system, as the universe

 

In our physical world, a structure may appear to be in equilibrium, but at a microscopic level, it is not in equilibrium at all.  Through entropy, any system seeks its lowest possible energy state.  Accumulating stresses such as vibration, thermal expansion and contraction, corrosion, and any other process all contribute to entropy.  Although a structure may appear solid enough – a building can stand for hundreds or even thousands of years – still, that structure is in the process of falling down, as eventually it must.  All structures that are currently standing will eventually fall.  To put it simply, whatever goes up must come down.  Similarly, a material that resists deflection (such as a spring) is also in a state of positive potential energy when under load, and that brings us back to classical guitar strings, and the sharpening effect.

The enigma I have been pondering since I first observed the sharpening effect those decades ago, is, how can a guitar string (in effect an extension spring), increase in tension by its own accord?   Through the mighty, irresistible process of entropy, a string should progressively lose pitch over time, all other things being equal.  It would appear that an increase in pitch represents a gain in the system’s available energy.  This represents a decrease in entropy, which is impossible, according to everybody.  Since it would be folly to imagine that the sharpening effect is the sole exception to one of science’s most inviolable tenets, it is safe to assume that the system (the guitar string and the guitar) is in fact achieving a lower energy state, although logic dictates otherwise. 

In order to eliminate bias and random chance from playing any role in my perception of the sharpening effect, I performed a series of controlled, objective tests.  It is beyond the scope of this article to fully document my methodology, however it is quite fair to say that I eliminated bias and random chance, and obtained statistically significant results, with a high degree of confidence that I was not merely imagining the sharpening effect to occur.  Under reasonably controlled environmental conditions, a BOSS chromatic tuner (model TU-12H) indicated that the sharpening effect occurred each and every time I tested for it, on every string, within one minute of drop tuning the string one step.  Repeated trials all resulted in the same indication.  The string does go sharp.  If I may, I will add my own (admittedly subjective) experience: I have noticed the sharpening effect on all my many guitars, ever since I first detected it decades ago.  In truth, not everyone to whom I’ve described the effect, state that they themselves have observed it.  I cannot claim that all guitars under all conditions exhibit the effect.  I can state that mine have, under varying conditions, as have others with whom I have corresponded.  I’m utterly convinced of its veracity.

Having stated that the effect is real, two questions beg to be answered: What can be done about the sharpening effect, and what is the explanation for it?

For the luthier, the sharpening effect can be safely overlooked.  There is no alteration to the standard design that suggests itself to me, nor would I be likely to recommend it, even if one did.  In the abundance of considerations about instrument building, the sharpening effect is a relatively minor annoyance, and trade-offs in much more important areas, such as sound, playability, weight, and tradition, might well be undesirable.

For the performing player, I have several suggestions.  For one (if it is consistent with your artistic goals), arrange your program to minimize the number of tuning changes.  Also, after a tuning change, play a short piece before a longer one.  Rather than D tuning and immediately launching into Capricco Arabe (when it will be a good 5 excruciating minutes before you can correct the string), play a shorter warm-up piece that employs the same tuning - such as Sounds of Bells or Canco del Lladre.  Then you can make a tuning correction if needed, and play the longer piece with confidence.  Once a string has suffered the sharpening effect, it seems to gain immunity until the next time you drop tune the string.  Another suggestion: you can minimize the effect by how you tune.  Drop the string a full step below the desired tone, give the string a few gentle tugs, wait a few patient moments (getting mentally ready to play the piece you are preparing the guitar for) and only then, slowly bring the string up to its final pitch. You may have to cut this short if the audience starts walking out on you.  As a last resort, you may have to tweak the string “on the fly” at a well-timed moment while playing. 

The question remains, what is the explanation for the sharpening effect?  Over the years, I’ve entertained many theories, yet I remain unconvinced.  The best of the lot is that the neck, soundboard, and other structures take up the deflection given up by the string when it is lowered.  Then those structures, seeking their initial state, transfer that deflection back to the string, making it go sharp.  While the idea  has some merit, it nevertheless violates certain beliefs about entropy as well as some principals of mechanics, and I remain unconvinced.  A fairly elaborate set-up of actuators, strain gauges, and a (not too expensive) guitar would be needed to test this idea, if anyone’s game.

Even under the best of conditions, guitars and other stringed instruments require constant attention to their tuning, for a host of reasons.  The sharpening effect is just one of them, and hardly the most significant.  But although not debilitating, it is a real phenomenon; not the product of my imagination or random chance.  Luthiers should probably disregard it, and players may make adjustments for it when feasible.  The main problem presented by the sharpening effect, is to answer that regal, ancient question that has spawned all science: WHY?

Home    Back To Ramblings