Thanks, I will try that exactly as you prescribed. I tried something like that a while back, but heard nothing. My cab seems to sound alright, though. I must say that I am playing passive basses, both with flats. But, my old Fender Bassman 150 has a piezo and lets me hear it, or not hear it when I turn it off. It's noticeable. Markbass specs say the piezo is crossed over at 3.5Khz. It says that for all their cabs, I think.