You got it backwards. The burden of proof falls on anyone claiming that wood does make perceivable differences in tone. I wouldn't say wood makes doesn't make a difference. I'm just not convinced that it does.If it can be demonstrated empirically that fretboard wood makes no difference in the tone coming out of a bass, as many assert, then it seems logical to conclude that the material in which the frets are seated does not affect the tone and therefore a fretboard made of dried mud (or bacon, or crusty gym socks, or cork) should sound exactly like one made of rosewood, ebony, maple, etc.