Alvaro Martín Gómez A. said:
Let's say you have a bass chart and there's a G on the fourth space. This means you should play the open G string, or the D string on the 5th fret, or the A string on the 10th fret, or the E string on the 15th fret. The written note is called G3, But what you hear is the G one octave lower, called G2. Now, if you have exactly the same bass chart but you add an 8vb mark, you must play the G on the E string, 3rd fret. The written note is still G3, but now, with the added 8vb mark plus the fact that the bass is a transpositional instrument which sounds one octave lower than written, the actual pitch now is G1 (two octaves lower than written). Hope this isn't confusing at all (let me know).