tuning
Tuning a piano requires both technical and artistic expertise. Modern pianos are almost always tuned to 12 Tone Equal Temperament – where every pair of adjacent notes has an identical frequency ratio. One octave (12 notes) is divided into 12 logarithmically equal parts.
Before Equal Temperament was widely accepted, other scales and temperaments were utilized to favor some of the more common keys, such as C major. The more just intonations of the 3rd and 5th intervals in these favored keys made them very consonant (or smooth). But modulate to any other key, and the dissonance of some of the intervals would make your spine tingle.
The 12 Tone Equal Temperament is, in fact, a compromise (not one interval in any key is technically “in tune” mathematically or aurally); but it is one that serves every key equally. The consonance and dissonance inherent in C major is geometrically and aurally identical to the consonance and dissonance inherent in Eb major – or any other key in Equal Temperament.
There are other “Equal Temperament” tunings (not nearly as universal), but the unqualified term “Equal Temperament” is assumed to mean the 12 Tone Equal Temperament.
Tuning a piano in Equal Temperament requires a delicate “tempering” of intervals in the 12 tone scale. Since I was trained in the “aural tradition” style of piano tuning, I tune by ear – and I use an excellent piece of computer hardware and software to check my progress (the computer doesn’t make me better - just faster). It is my strong belief that a good aural tuning trumps a “computer” tuning any day. Aural tuning takes into account all of the psychoacoustic phenomena (how we perceive sound) and inherent physical limitations (such as string inharmonicity) that surround the imperfect beast that we call the piano.
“So, why does my piano go out of tune?” you may ask.
Short answer: Climatic changes (temperature and humidity), playing it, and moving it.
Long answer: the strings of a piano are stretched across a “bridge” that is in turn attached to the sound board (almost always spruce), which serves to amplify and add tonal characteristics to the vibrating strings. Each of these 200+ strings is carrying a tension (at pitch) of somewhere between 150 and 200 lbs; a quick calculation shows that your piano is under constant stress from around 20 TONS of tension!
(if you’ve ever wondered why there’s a huge plate of gold-painted cast iron in your piano - that’s why; without it, your piano would just fold in half!)
For the sake of acoustical coupling of strings to wood, the soundboard is purposefully “crowned” (convex in the direction of the strings) in order to create “positive downbearing” from the strings; in other words, to get nice, strong tone, the strings need to be pushing down on the bridge/soundboard. So far so good.
BUT, when atmospheric changes occur (humidity is the biggie, followed closely by temperature), the crown of the soundboard will rise or fall. Ever. So. Slightly. But it’s easily enough to affect the tension of those strings that were only a short time ago
meticulously adjusted by a qualified piano tuner! And voillà - out-of-tune piano!
Understanding the unstable and antagonistic nature of strained steel wire, tenaciously pressing on a thin sheet of spruce, and all held together by wood and iron (remember “potential energy” in 6th grade science class?) - you don’t need me to elaborate on why moving a piano - or even just playing it - will affect its state-of-being-in-tune. William Braid White, in his definitive work, Piano Tuning and Allied Arts, takes this concept to the Nth degree:
From a strictly scientific point of view, it is probably true to say that no piano ever made has stood in tune, without a drop or a rise for more than twenty-four hours, unless it were maintained at constant temperature, and under constant barometric and hygroscopic conditions in a laboratory.
