Why Does a Piano Go Out of Tune After Tuning Due to Environmental Factors?

Jan.15, 2026  Mr. Huscher

 

A piano can still go out of tune after tuning due to environmental factors, primarily because of the dynamic imbalance between the physical properties of its materials (especially wood) and the enormous physical tension under changing environmental conditions. Here are the specific reasons behind this phenomenon:

 

The Impact of Humidity Changes on the Soundboard (Core Reason)

The pitch of a piano is highly dependent on the physical state of the soundboard.

 

Strunz soundboard

• Increased Humidity: Higher humidity causes the wooden soundboard to expand and arch upward (increased curvature). Since the strings press down on the soundboard via the bridge, the upward movement of the soundboard further increases the tension of the strings, raising their pitch.

 

• Decreased Humidity (Dry Conditions): When the environment becomes dry, the wood contracts, and the arch of the soundboard flattens, reducing string tension and lowering the pitch. Even if the soundboard is coated with lacquer, its response to humidity is only delayed, not entirely prevented.

 

Differential Reactions of Wood and Metal Framing

The piano’s structure, comprising wood and metal (the iron plate), supports approximately 20 tons of tension.

 

• Differences in Thermal Expansion and Contraction: Significant fluctuations in ambient temperature affect both the iron plate and the wooden case. Atmospheric changes often impact the iron plate and wood in opposite ways—for instance, while the iron plate may contract, the wood might be expanding. Such inconsistent deformation disrupts the initially stable tension balance.

 

• Deformation of Back Posts and Pin Blocks: Environmental factors can cause slight warping or compression of the wooden back posts and shrinkage or tilting of the pin block. These minor shifts in mechanical positioning contribute to the loss of tuning stability.

Chloris Piano Frame

 

Physical Properties of Strings and "Creep"

• Continuous Stretching: Under tremendous tension, piano strings gradually stretch until their elasticity is entirely lost after several years.

• Stability of New Pianos: New pianos require frequent tuning during the first year because new strings continue to stretch, and the action and overall structure have not yet fully settled into a "completely released" stable state.

 

Stress Adjustment After Tuning

• Redistribution of Tension: During tuning, the strings experience uneven tension distribution at contact points such as the tuning pins, bridge, and capo d'astro bar. If the strings do not slide smoothly over these points, the tension will self-balance during playing, causing the pitch to change (usually rising).

• Optimal Timing for Tuning: I recommend tuning a piano after significant weather changes. For example:

 

In northern China, it’s best to tune the piano in the second or third week after indoor heating begins in winter or after it ends.

 

Another suitable period is one to two weeks after the onset of the rainy season.

 

In southern regions, tuning should be scheduled after the humid "returning south" weather or the rainy season, not before.

 

In summary, a piano goes out of tune mainly because its soundboard acts like a "breathing lung," constantly altering string tension in response to humidity changes. Simultaneously, the differing reactions of wood and metal to environmental conditions, coupled with the natural stretching of the strings, collectively cause fluctuations in pitch after tuning.

Chloris baby grand piano