Every year around this time, the instruments in our shop tell us that the season is changing. They tell us that the heat has come on and is drying out the air, and they tell us this in a variety of ways: pegs are shrinking and thus slipping, causing the tension to release from the bridge. Bridges are then free to move about, and sometimes even fall over. With the string tension released from the bridge, the sound post is freer to move or fall over. The result is a big mess that can take time to rectify; with as many instruments hanging for sale as we have here at our shop, it can take days to rectify.
Summer has faded into fall and winter is approaching. The heat is coming on in our houses. Pegs are beginning to shrink, and so is the top and back of our instruments. As the back shrinks to its winter setting, the neck angle rises, causing the strings to get closer to the bridge. This is especially true for cellos and basses, but also for violins, violas, and other stringed instruments with necks. The shrinkage of the top causes the sound post to be tighter, sometimes resulting in a more shrill sound, a more brittle type of sound. The drying can also cause glue seams to open, particularly at the upper and lower bouts where the string tension is concentrated.
Today we set up our humidifiers throughout the shop building. Ideally we would like to see the humidity level to be between 40 and 60%; this tends to keep the instruments steady. Instruments will slowly adjust to the change of season, but must be checked for slipping pegs, tight sound posts, open seams, moving bridges, and changes in neck angle. Your instrument will tell you when it is not happy or something is not right; the sound changes and the response is not what you expect, much like your car lets you know when something is not right. Keep your ears and eyes open, and take good care of your instrument as it makes the transition from heat and humidity to cold and dry conditions.