Going on the basis that electric guitar and electric bass are similar in the way they work, I have to say yes the guard does effect the sound I am still trying to figure out to what degree though.I built a guitar out of parts allover the place it consists of 7 guitars worth of odd parts working in harmony,well its a Ibanez RG body with a Les Paul humbucker,I had a good friend construct a pickguard for this musical oddity and he came back with a bronze pickguard,The strings echo much louder than say a strat which to my mind would be a fair comparison,I am still trying to determine how much difference with the amp factored in,I guess I will have to get a Phat strat to continue this test but yeh the guard can change the sound from my experience