how often should a piano be tuned?

Well there's the short answer or the right answer. The full story is a little complicated, so most tuners give customers the rough rule of thumb, which is twice a year. In truth though, the correct tuning interval will vary from one situation to the next. To get the full picture we have to understand a little about the design and construction of the piano. 

Pianos have around 230 thick steel strings which are stretched across a raised wooden bridge, much like on a violin or guitar, but whereas a violin has a few pounds of tension the piano generates around 20 tons of strain across its iron frame. This force pushes down on the bridges and then the soundboard, which is only fixed at the edges, so it can resonate. As the tension increases,the soundboard and bridges move around a little to accommodate for the increase in tension. 

What this means for the tuning is that after some time, when the internal geometry of the piano has settled down, the tuning will have shifted and the instrument will sound a little flat. Raising the pitch of a piano is a big deal, just a few Hertz of pitch increases the tension by several tons. This destabilizes the instrument and means that it will not stay in tune for as long as it would have if it had been fine tuned without doing a pitch raise. So going back to our original question, the piano should be re-tuned, before the pitch has dropped so far that it needs a pitch raise tuning every time. Some less conscientious tuners don't bother to do the extra work required to put the piano back to concert pitch, (A440 Hz) which leads to a gradual loss of pitch and means the piano is not in tune with other instruments. This can be detrimental to the natural perfect pitch some children are born with, as well as creating several other practical problems and issues.

The worst situation is when the customer decides when the piano needs tuning, based on how it sounds to them.

This always means too long a gap and the piano usually either needs a more expensive pitch alteration or the pitch of the piano leaks out with every subsequent tuning. Remember a piano can only be tuned properly, when it is already nearly in tune. If the pitch of the piano has to be altered every time it's tuned, then the strings never really settle and fine precise tuning is impossible. 

Alternatively if the piano is tuned just before it needs pitch raising, the effect of the tuning will be much better and the piano will stand well in tune for longer. 

The best thing is to ask your tuner for the correct tuning interval for your particular piano. This will be based on the amount it is played and it's general condition and age. The environment also plays a huge part, changes in humidity cause the soundboard to move around and this has a major effect on the tuning stability.

If a piano is tuned regularly there is less wear on the pin block and the life of the piano will be dramatically increased as well as getting the best possible sound and performance from your instrument. 



information taken from www.stevedroy.com