Hi there. Iam a piano tuner. I can answer some questions. 1. Humidity or the lack of it is a problem for pianos. In a dry climate we use humidifiers to add moisture to the piano mostly the sound board. 40 percent inside the piano is what they want . Keeping it regulated at that level is the key. In a humid situation heating element rods are used to remove the humidity again to 40 percent. The sound board is made of spruce like a big guitar top. Spruce is very porus wood and absorbs moisture quickly when it does it expands the piano bridges are hard rock maple which are glued to the soundboard. When the board expands or contracts the bridges move also which throws the piano out of tune. 2. Tuning - unisins are always tuned beatless, no audible waves.The temperament is your middle 12 notes,. tThis is where it gets complicated. Octave in the middle temp is tuned beatless. 5ths beat the slowest-about 3-5 beats every 5sec- 4ths are faster but not by much- 3rd are paster but not by much- 5th -4th- and 3rds are stagered meaning above 0 or below 0 depending on the root note and the note to be tuned. Actually it was beethoven who came up with the temperament tuning. You see if you tune everything without any beats chords will be out of tune, so a pleasing compromise had to be found. That why even guitars can not be tuned perfectly . This is called inharmonisity!
Hope this helps some Paulieg
