I bought a used Acme Low B2 on ebay and gigged with it once. It sounded really good, and I had the high and mid attenuator knobs set at 12 o'clock. I didn't goof with them at all. At rehearsal today, I decided to fiddle with both knobs and see how they affected the sound. But, the drummer, guitarist, singer and myself could not hear any change in sound when either knob was wide open or off. Granted, we were not cranking at gig volume, but even when it was just me playing and the drummer adjusting the knobs, nobody could hear any difference. Could the attenuators be disconnected or broke? Is the effect supposed to be subtle? Does it make a difference that I'm playing an upright? I didn't have my P bass to try it. Any thoughts?