Pianos are not perfectly in tune for a combination of fundamental acoustic reasons, a necessary tuning system compromise, and various factors that cause them to drift out of tune over time.
Why Pianos Cannot Be Tuned to a Mathematically "Perfect" Standard
Even when freshly tuned by a professional, a piano can never be perfectly "in tune" in the absolute mathematical sense across all its notes and intervals simultaneously. This is due to two primary reasons:
The Challenge of Inharmonicity
Unlike ideal strings, piano strings are stiff and thick, which causes their overtones (or harmonics) to be slightly sharper than true integer multiples of the fundamental frequency. This phenomenon is known as inharmonicity. If a piano were tuned such that all fundamental notes were perfectly in tune, their overtones would clash, sounding unpleasant. Tuners must strategically "stretch" the octaves, making higher notes slightly sharper and lower notes slightly flatter than their theoretical perfect pitch, to create a more pleasing sound that accounts for this inharmonicity. This compromises perfect mathematical intervals for a more aesthetically acceptable sound.
The Compromise of Equal Temperament
The most common tuning system for pianos is equal temperament. In this system, the octave is divided into twelve mathematically equal semitones. While this allows a piano to be played in any key without sounding drastically out of tune (which is not possible with older tuning systems), it means that no interval (except the octave) is perfectly pure. For example, a perfect fifth in equal temperament is slightly flatter than a mathematically pure perfect fifth. This slight deviation is distributed across all intervals, making all keys equally imperfect but playable.
Why Pianos Don't Stay Perfectly In Tune Over Time
Beyond these inherent challenges, pianos constantly go out of tune due to a variety of physical and environmental factors.
Material Changes and Wear
The components of a piano are constantly under stress and subject to change:
- Newer Pianos: Over time, the substantial tension from the strings can cause them to gradually stretch. Simultaneously, the wooden components within the piano's structure, which support this tension, can compress. This combination typically causes the piano's overall pitch to gradually go flat.
- Older Pianos: In older instruments, the critical tuning pins—small, tapered metal pins around which the strings are wound and tightened—can become loose within the pinblock. When these pins can no longer hold the strings at their intended tension, the piano will not hold its tune effectively and will sound flat or simply fall out of tune more quickly.
Playing Habits
How a piano is played significantly impacts its tuning stability:
- Frequent and Hard Playing: Repeatedly striking the keys with force, especially in the same registers, can cause the strings to stretch more rapidly or even slip slightly on the tuning pins, leading to those notes going out of tune faster. The vibrations and impacts from playing can also subtly shift the instrument's structure.
Environmental Fluctuations
Pianos are highly sensitive to their environment:
- Humidity and Temperature: Wood, felt, and other materials within a piano expand and contract with changes in humidity and temperature. This movement directly affects string tension and the stability of the soundboard, bridge, and pinblock, causing the piano to go sharp or flat as conditions change. Significant fluctuations are a leading cause of pianos going out of tune.
Factors Affecting Piano Tuning Stability
Here's a summary of the key reasons pianos are not perfectly in tune or drift out of tune:
| Factor | Impact on Tuning | Reason/Cause |
|---|---|---|
| Inharmonicity | Causes overtones to be sharp, requiring octave stretching | Physics of stiff piano strings |
| Equal Temperament | Deliberate compromise; no interval (except octave) is pure | Allows playing in all keys, a necessary system for fixed-pitch instruments |
| String Stretch | Strings gradually lengthen, lowering pitch | Constant tension on strings, especially in newer pianos |
| Wood Compression | Wooden frame parts compress, lowering pitch | High tension from strings on structural components, especially in newer pianos |
| Loose Tuning Pins | Pins lose grip, cannot hold string tension | Wear and age in older pianos, or humidity changes |
| Playing Intensity | Physical stress on strings and action | Frequent or hard playing |
| Environmental Changes | Expansion/contraction of materials | Fluctuations in humidity and temperature |
Maintaining Piano Tune
Given these factors, regular professional tuning is essential to keep a piano sounding its best. A skilled piano technician not only adjusts the pitch of each string but also accounts for inharmonicity and equal temperament, making subtle adjustments to achieve the most pleasing sound. Additionally, maintaining a stable indoor environment (consistent humidity and temperature) can significantly reduce the rate at which a piano goes out of tune.
