| A change of season is often accompanied by a change in relative humidity. As the humidity increases, the wood of an instrument abosorbs moisture and swells slightly. The wooden neck of a bass will tend to straighten out as it swells, negating the relief or even going into a slight backbow.
For most players with wooden-necked instruments, that means we usually have to do a setup at least twice a year - once as the humidity increases and once when it decreases.
Alternatively, you can put a bit more relief in your neck than usual and raise the bridge saddles quite high and never have to worry about this again. You won't like it though if you like low action.
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Instrument Technician, Toronto
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