Tuning and Pitch Correction

Why does a piano go out of tune?

In short, because of the weather.

Your piano is made largely of wood, and wood is a material constantly in flux. Wood changes dimension when the temperature and especially when the humidity in the surrounding environment changes. You may have experienced a wooden door frame swelling and the door sticking shut because of increased humidity in summertime; this is because wood absorbs and desorbs moisture according to the air surrounding it. The piano's soundboard (the panel in the piano that transmits the energy from the strings into the air similar to a stereo speaker) is very sensitive to these humidity changes. It swells in humid summer months and because it is in contact with the strings the soundboard introduces extra pressure into the system, subsequently making the pitch go up. The opposite happens in the winter; the soundboard shrinks and the pitch goes down. It just so happens that the piano usually doesn't recover as strongly to the downswing in pitch from the dry winter months, so the overall net effect of the seasonal change is typically a drop in pitch over time.

Pianos are designed to be tuned so that the A above middle C is vibrating at 440 cycles per second. This is an international standard for orchestras and musical instruments in general; the standard is also called 'concert pitch'. It's important to keep a piano tuned at concert pitch for a few reasons:

• The instrument will match in pitch with other instruments for ensemble playing.
• A musician's ear is always evolving; this is especially the case with young children. People need an accurate reference for ear training and an piano at correct pitch ensures this.
• With the pitch at A-440 the tensions and structures of the piano are at equilibrium for which it was designed which encourages tuning stability over time and insures that the instrument is in a state of optimal maintenance.
• Last but not least, the piano will have the most power and the most beautiful tone at the pitch in which the factory intended.

Whew. Well, all this just begs the question...

How often does a piano need to be tuned?

Most manufacturers recommend that a piano should be tuned four times in its first year after being delivered from the factory due to strings stretching and other internal parts coming to an equilibrium state under the enormous tensions of the strings.

After this first year, the manufacturers recommend having a piano tuned twice per year (remember those seasonal humidity changes?), depending on the frequency of use and demands of the playing conditions.

Why would my piano need a pitch correction? And, what does this have to do with my shoes?!

If a piano's pitch has deviated considerably from concert pitch at A-440, it could require a pitch correction. When the pitch drops a significant amount, the amount of over tension of the strings is decreased. It's impossible to add a lot of tension at once and have the piano stay at a stable pitch because what I call the "shoelace effect".

If your shoelaces were very loose and you just tugged strongly at the ends of the laces, the top segments of the laces would be tight and the segments closer to your toes would have more slack. As you walked around over the day, the tension in these segments would equalize a bit more but still be looser than you intended when you tied your shoes. Instead what we do is pull the lower segments a little bit, then the middle ones, then the top segments; this creates stability and you know that your shoes will stay at the higher tension you intended them to be in the first place.

This is analogous to what I am doing to a piano when I do a pitch correction. I bring the piano close to pitch just as you would add tension from the bottom to the top when tightening a shoe. Then, once the average pitch of the piano is in the right range and the overall tension of the strings are correct, I can apply a complete tuning that will remain stable over time.