From the Steel Guitar Forum:
** Note: When installed in vintage amplifiers and modern versions of classic amplifiers, the TSNEO 12-8 offers a slightly fatter bottom end than the old JBL’s so it is necessary to pull the bass control down very slightly in order to achieve the same balance of lows to highs as the JBL K series speakers. If this is not done, the listener may get the impression that the TSNEO 12-8 offers less highs than the JBL K120-8 due to the dominant lows.
By pulling the bass down slightly, the same balance between the low and high ends is achieved.
(In other words, the two types of speakers will not sound the same if they are simply “switched” without making this adjustment.)
Wouldn't this be a problem for a Jerry player with a bass control already set at 0?