Michael, I just completed K2 S/N 4031 with the 2.2 kHz. filter. It is excellent, very normal sounding voices. I also have K2 S/N 2676 with the standard 2.0 kHz. filter which while good, is not nearly as normal sounding as the wider filter. Definetly build it with the 2.2 kHz. filter to begin with IMHO. I believe 2.5 kHz. is too wide. Have fun, you won't be disappointed. 73, Bob VE3XM