You may have asked yourself the question; why do I need to get my piano tuned even if no one is using it? I will cover a couple of the biggest reasons in this post. First of all, humidity is the single biggest factor in a piano's tuning stability. Without getting overly technical, a soundboard in a piano has what is called "crown". This is the slight curvature that is imparted on the soundboard to add compression and in turn make the panel better able to amplify sound. Think about it like an arch top guitar. As you can see in the picture below, the ribs are used to put crown in the soundboard and help hold it in that position over time. Maybe we will cover soundboard construction in a future post. In the summer, the spruce in the panel takes on more moisture because of high humidity and the crown becomes greater. This causes the pitch of the piano to rise especially in the middle register. In the winter, because of low humidity, the exact opposite is the case. In North Carolina we have a very strong seasonal change so many times tunings are necessary twice per year to maintain a stable instrument. Sometimes installation of a humidity control system is a must as well. More afer the image below:
The second reason to get your piano tuned at least once per year is to maintain the pitch of your instrument. Pianos are designed to be tuned to concert pitch which generally range from A440 to A442. Even if you don't play the piano, the pitch will gradually drop because the stings relax as does the soundboard panel. The longer you the piano goes without being tuned, the flatter it gets. If the piano hasn't been tuned for a few years, it is likely that more frequent tunings will be necessary to get the piano stable again. Essentially you have to retrain the piano to stay at concert pitch. Yearly tunings insure that the piano will always stay close to concert pitch.