Pianos are under a tremendous amount of tension, about 20 tons actually. That's Right!!
40,000lbs of tension is strung across the average piano. While fighiting all that tension and with the ever change of temperature and humidity, the piano is consistantly conspiring to drift out of tune.
The primary reason for routine piano tuning is to keep the piano sounding good to our ears! The secondary reason for regular piano tuning is to ensure the combined string tension is equalized against the soundboard, bridges and cast iron plate throughout the piano. When the strings are set at the right tension then the piano will be in tune and under normal conditions will help your piano last for many musical years to come!
As humidity goes up in Dallas during the beginning of May, a soundboard swells, increasing its crowned shape and slightly stretching the piano’s strings to a higher pitch. During dry times, usually in midsummer and dead of winter, the soundboard flattens out, lowering tension on the strings and causing the pitch to drop (or go flat). Unfortunately, the strings don’t change pitch equally. As the soundboard and bridges 'expand and contract' with changes in weather, every piano is always going out of tune! For this reason, pianos should be tuned at least once a year even if no one is playing it. In this way, the parts of the piano remain correctly aligned, preserving not only the beautiful tone but increasing the life of the piano by preserving the structural integrity of the instrument.