Humidity Explained
If you tune in summer the bass sounds sharp in winter.
If you tune in winter the bass sounds flat in summer.
The reality is the bass section does not move much the treble section shifts sharp or flat which contrasts against the bass.
Why
Wood shrinks and swells with humidity changes.
The pitch of the piano plain wire increases with humidity and decreases when it is dry.
The further away from 45% humidity the more drastic the effect on the tuning at the opposite time of the year.
The closer to 45% humidity when you tune the better.
It is not uncommon to have pianos do a 1/4 to 1/2 step swing sharp or flat when the humidity changes either direction.
If you tune in winter the bass sounds flat in summer.
The reality is the bass section does not move much the treble section shifts sharp or flat which contrasts against the bass.
Why
Wood shrinks and swells with humidity changes.
The pitch of the piano plain wire increases with humidity and decreases when it is dry.
The further away from 45% humidity the more drastic the effect on the tuning at the opposite time of the year.
The closer to 45% humidity when you tune the better.
It is not uncommon to have pianos do a 1/4 to 1/2 step swing sharp or flat when the humidity changes either direction.
The soundboard
Manufactures build the piano with a curve in the soundboard intended to be its best at 40-50% humidity. Unfortunately in MN that level of humidity is rare and as a result most pianos spend their usable life in an untuned state.
Soundboards have three states.
Most people see a piano. Believe it or not, there are three instruments in one because the soundboard changes shape with the seasons.
What happens in winter?
The dry condition, moisture leaves the soundboard and the instrument becomes flat, the bass section and octaves do not sound right as the midrange pitch has fallen below the bass. It is not uncommon for the first snow of the season to arrive and for about a week the piano sounds ok, but once the moisture content of the soundboard shifts, the tuning shifts and (almost) overnight the moisture content changes from 40% humidity to 15% humidity. The colder it is outside the quicker the shift the the dry condition.
What happens in summer?
The humid condition, the soundboard absorbs moisture and the midrange pitch rises above the bass once again the bass octaves vs the midrange sound funny. The bass seems flat but the pitch the piano is now drifted sharp.....
How about spring or fall?
The soundboard is anywhere in-between the winter condition and the summer position. When you tune, the closer to 45% humidity the better. The further away from 45% humidity the more drastic the effect at the opposite time of the year.
Ironically this is one of the best times to tune an instrument but most pianos are sounding ok to the owners so they decide to wait.
Ironically this is one of the best times to tune an instrument but most pianos are sounding ok to the owners so they decide to wait.
All Photos and graphs on this page are used with permission of the Dampp Chaser corporation.