In the short term, leather and felt compact, affecting the adjustment (regulation) of the parts. The action becomes uneven and less responsive, and the piano's tone loses dynamic range. Squeaks and rattles may develop. Routine maintenance such as hammer filing, regulation, voicing, and tuning will correct these problems and maintain the piano in near-new condition.
After extended or very heavy use, action parts become severely worn. Leather and felt to wear thin. Keys become wobbly, hammer felt gets too thin to produce a good tone, and the action becomes noisy. Regulation adjustments reach their limit. In addition, piano strings may begin breaking and the copper windings of bass strings lose resonance.
After decades of exposure to seasonal changes, the wood of the soundboard, bridges, and pinblock is weakened. This causes loose tuning pins, poor tuning stability, and further loss of tone. By this time the piano's finish will often be scratched or faded.
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