The short answer for the main cause in two words: HUMIDITY CHANGE.
The longer explanation of why this is so:
Even though the heavy cast plate in the piano (usually an iron/steel alloy) is designed to bear the brunt of the thousands of pounds of tension from all the strings, the majority of the remaining components in the modern piano are still made of WOOD.
All the strings pass over WOODEN bridges, which in turn are attached to – and transfer the sound to – a WOODEN sound board, much like a larger version of the top of a guitar. Add to this the fact that the tuning pins (which tighten and loosen the strings for the correct pitch) are set into a multi-ply HARDWOOD block variously named a “pinblock” or “wrestplank.” To top it all off, everything is tied down into a WOOD case, be it grand or upright.
Now imagine in your home what may happen to your kitchen cabinets, doors, window sashes, and hardwood floors throughout the seasons. As time goes by, you may notice things like doors sticking in the summer, or cracks opening between the floorboards in winter. These, of course, are all due to – you guessed it – HUMIDITY CHANGES.
Depending on the area in which you live, those changes can be dramatic or almost non-existent. There are areas in the U.S. that can remain relatively dry throughout the year, and others consistently humid. In these areas, good quality pianos can generally stand in tune longer than elsewhere. The majority of the country, however, is subject to seasonal changes, and these changes can have a dramatic effect on tuning stability.
Wood draws in moisture from the air in a humid summer, causing it to expand (making those doors stick), and this moisture gets evaporated out of the wood as relative humidity goes down in the winter months. Add home heating to this already dry air, and the drying effect is compounded (opening spaces in the floorboards).
Since the majority of a piano is made of wood products, it is, of course, going to behave in a similar fashion. Even though most piano manufacturers go to great lengths to procure the highest select woods, and go to great pains to age, dry and season them, it doesn’t change the basic structure: it’s still WOOD, and each piece may respond to humidity changes differently.
Soundboards – and to a lesser degree, pinblocks – will expand and contract, sometimes even with the slightest humidity change, and it is this shrinking and swelling throughout the seasons that will cause your piano to eventually “go out of tune.”
My recommendations to clients:
Of course, the BEST solution for better tuning stability would be to put the instrument into as much of a climate controlled environment as possible. Keeping the air moisture level between 40-60% is optimal. If you can’t afford a whole-house humidity control system, there are other steps you can take to at least minimize the extreme changes:
When possible, devote your piano to a small(ish) room that can be closed off. Purchase a room de-humidifier suitable for the room size that will keep the moisture down during the summer (air conditioning will help as well). Also purchase a HUMIDIFIER to ADD moisture during the dry winter months. Some forced-air heating systems can have humidification added to them – but shop around for the one that works best. Again, if you can keep the room humidity to between 40-60%, you’ll be doing the best for your piano.
The next best thing would be to purchase a piano humidity control system, which actually attaches to the piano itself. This can be a useful solution in many situations, though you should always consult a reputable technician to determine if this will meet your needs (*yes, we sell and install these!).
Can’t afford any of these options? Here’s more you can do simply to help:
Always place the piano on an interior wall or in an interior room, away from all heating apparatus (ducts, baseboards, radiators, fireplaces, etc., which tend to be on outside walls).
Keep the piano as far away from open windows in summer as is practicable.
Keep your heat DOWN as much as possible during the winter. The lower the heat, the less dry your house (and your piano) will be. Remember, as the saying goes: “It’s not the HEAT, it’s the HUMIDITY!”
If you have a wood stove, keep a kettle full of water on it.
If possible, in winter keep a lot of houseplants (yes, HOUSEPLANTS!) nicely watered in the same room NEAR (never ON!) the piano. Your piano (and perhaps your health) will love you for it!
Finally, if you can do none of the above, realize that you will simply need to have your piano tuned much more frequently than otherwise would be normal (twice yearly is the norm, more often as needed).
Article by C.L. Young ©2012