Check out Standard Bass Guitar Tunings, too.
What is the purpose of using non-standard bass tunings?
The most common reason is to get notes you could not otherwise play. Sometimes you just need that lower note to make something sound the way it needs to sound. For instance, on a 4-string bass the open string D is the lowest D note you can play in standard tuning. It’s really not all that low. So, many people will play in “drop D” where you tune the open E string down to a D.
Another reason is to match the guitar player’s tuning. Some guitarists, like Stevie Ray Vaughn, tune down all their strings a half-step making the strings looser and easier to bend. A lot of today’s guitarists use drop D so they can play the one-finger power chord with ease and to get that lower, heavier sound. So the bassist might need to match the guitarist’s tuning to get the proper range of notes.
Changing the tuning can cause all the scale and arpeggio fingerings to change. A different tuning can help you to play notes you might not have otherwise been able to play. In the StudyBass tools section, you can view fretboard diagrams of scales and chords/arpeggios for any tuning.
Altered 4-String Bass Tunings
Since the 4-string bass has the smallest range of notes (nothing wrong with that), it gets tuned differently most often. You can “drop” the E-string to an Eb, D, Db or even a C.
Sometimes you can detune all your strings a half-step or a whole-step. This will preserve all your scale and arpeggio fingerings.
Another common approach is to tune a 4-string like the four low strings of a 5-string bass B E A D. From there you might even drop the B to an A or tune them all down a half-step.
Altered 5-String Bass Tunings
Tunings similar to the 4-string altered tunings exist for 5-string basses. You might tune the standard tunings down a half- or whole-step. One of my favorite tunings is the standard high C tuning tuned a whole step down. If you find the low B too low for your taste, you might like this tuning.
Altered 6-String Bass Tunings
Again, you have quite a range of notes with a six string bass. You might tune down a half- or whole-step though.
There are no rules to tell you how to tune a bass. Sometimes experimenting can yield interesting results. Try whatever bass tuning you can dream up. Just don’t over tighten your strings and break them. Remember, you need heavier strings for lower notes and lighter ones for higher notes. Also, check that your bass can play in whatever tuning you’re using. Check that the intonation of your bass is good all over the neck (or at the very least the region you play in).