If you're after one of those rubber thingies to hang in your bass to keep up the humidity, I have them. They consist of a perforated non-vinyl tube with a sponge material inside, with a disk on the end. You soak it in water, squeeze out the excess, wipe it off, and hang it inside your bass though an f-hole. Natural evaporation transfers the moisture into the inside of the bass. But the question is... do you really need one?

If you have a laminated (plywood) bass, no. Carved or hybrid (carved top), yes.

The whole idea really applies only to carved basses, whose massive tops and backs can shrink or swell significantly when humidity drops or increases beyond the usual environment. If my old carved Juzek bass is used to normal or average summer humidity here in Southern New Jersey, when winter comes and my forced air heat comes on, the mental alarm bell goes off. Indoor humidity drops like a rock, causing moisture to gradually leach out of the wood, causing that top or back to shrink -- that puts pressure on the whole structure. If I'm lucky (and my bass seams are glued properly), the thinner mix of hide glue at the seam lets loose-- sort of an organic safety valve. The fix for that is usually an inexpensive one.

However, if I'm not lucky, "Crack!" goes the bass. "Rats!" goes Bob. Bob goes to the luthier and pays him potentially very big bucks to repair that ugly crack, which will haunt him forever. Bob says "Rats!" (or another, more colorful phrase) again. Laminated (plywood) basses were developed for this very reason. Their more stable woods don't move with the weather enough to be concerned, since they are not solid wood, so you don't expect them to crack under those circumstances. That said, extreme conditions aren't good for any instrument. Very high heat and humidity can affect the hide glue, causing seams to separate, and it is possible that extremely dry weather could affect the typically solid wood endblock, though it doesn't happen often.

These little hose doohickeys (Dampit and generic versions) can be a mixed blessing. First, you have to constantly watch them and remember when you last dunked it, and unless you have an accurate gauge, you really don't know how dry the house's environment is. But they have their uses and can be effective if used faithfully; however, some luthiers smile when they get to charge the overly faithful for cleaning the mold out of the inside of too-humid basses when overenthusiastic users don't exercise enough care. They are not necessarily a bad idea as an on-the-road precaution if the bass is out and about for a long while, but don't worry about taking your bass to a gig without one, it shouldn't be a problem over that short exposure - unless you're playing an outdoor gig at the Arctic Circle. But it could be a great conversation piece when your fellow players see it and ask, "What's that??".

If you've got a carved or hybrid bass, my suggestion is to get a household humidifier at your local XMart or equivalent, one with a built-in humidistat. I've got a couple different models that I picked up for around $50-60 each, and keep them where I store my basses and I have one in my bedroom to keep my pipes moist (well, my throat, I don't have pipes any more). Both my humidifiers have digital readouts that show the humidity in the room and let me set a target number. The units automatically go on and off all by itself to maintain the setting (I go for between 30% and 40%. IME it's better to get one with a humidistat with a digital display - those I've bought with dials don't seem to have precise enough sensitivity. I have had a couple different humidifiers in our large home living space, where I have an electronic humidistat to monitor moisture, and on/off cycles can vary by 15% or more. Spend the extra bucks and get a good one, keep it clean and it'll last a few seasons.

All I need to do is remember to refill it, and their angry little flashing lights as well as a low humidity number reminds me. It's a great excuse to keep your bass safe in your bedroom, because you then can humidify it and your lungs at night and not wake up with that dry and scratchy throat on those brutal winter mornings. At least that's what I told my wife. Just a note-- if you are going to put one in your bedroom, don't get a cold water evaporative unit, as the fan going on and off at night can disturb your sleep. The hot steam type are usually relatively quiet.

Now go forth and humidify! (IF you need to)

As of January 7, 2008 I have a Honeywell HWM450 Quick Steam Warm Moisture Humidifier in my bass room; this is the second season for it and it's doing fine. This is a statement not a recommendation, all I can say is that it works for me and is under $60 at Amazon. I got a package of Honeywell HMP-12P QuickSteam Mineral Absorption Pad so I can use it with tap water. This is just an example, there are many others out there.