Summary

My new acoustic guitar is unhappy in the dry winter air, and the strings buzz badly. So I made this humidifier, which holds a damp sponge. By putting it in the case with the guitar, the guitar wood is re-humidified and the strings sound great again! (Now I just have to learn to play it...)

Note that this is sized for the sponges I happened to have. You may want to scale it as necessary for your sponge.

For more on guitar humidifiers, this site has some good information.