I have fender fretless j-bass and recently, i changed flatwound string to roundwound(d'addario -XL 4 strings)...I didn't like that dummy of flatwound sound(?). anyway since i use that roundwound string...ah~i adjusted neck with a capo and feeler guage, but soon i noticed there is BUZZZZZZ(which is on G string at 19th fret!) but funny thing is only 19th on G-string is buzzinng. rest of them(includes 18th or 20th position) they sounds just great!!!! except 19th position. only that 19th position has too much buzzing. neck is straight...relief is 0.012mm. can someone please rescue my 19th position from evil-buzzzzz? please....
It is possible that the neck relief and neck angle are such that it could cause a buzz just one position, especially that high up the neck. You might try a small adjustment. Perhaps 1/8 turn or less of Less relief. You will of course have to set the action and intonation again after this. But, if it only occurs in a single position, it is more likely a high spot in the board. Just like there are high frets, there can be high spots in the fingerboard. You see this all the time with upright basses. One option is to simply raise the action of the string a bit. The other is to have a tech plane the board. Chas
BUT roundwounds + fretless = ( e.g. they sound great ) if it is a very small area that is buzzing you can hit it with a little sand paper or steel wool. The best if it's really bad is to have the board leveled like Chasarm said.