How much humidity is too much for a double bass? How much is too little? Do I need Dampits? Do I need to run humidifiers in the house? How about in the summer? Do I need a dehumidifier?
These are question every bass owner asks, and the answers are not really that clear. Some bass luthiers advise against using Dampits (green rubber tubes with sponges inside them to add humidity), claiming that they do nothing except damage the instrument by dripping and banging around inside. Other luthiers advise bassists to use four, five, or even six Dampits during the colder months (when homes are running heat). Few luthiers recommend using Dampits in the summer (or whenever the heat is turned off for the season).
Regardless of whether or not one uses Dampits, one should take care to keep a good level of humidity in the area that the bass is stored, and to avoid sudden drops in humidity and temperature (Minnesota in the winter is probably the most hazardous environment in the continental U.S. for basses) as much as possible. Most experts recommend keeping a room at 30-40% humidity. A drop below 20% is usually considered hazardous.
Bad things happen when the humidity and temperature drop suddenly and unexpectedly. This past winter in Chicago a week of bitter, dry cold set in, and after that week four of my students came into their next lesson with new cracks or open seams on their basses.
Also, check out David Gage’s excellent article “Heat and Humidity“.