Long answer: you have to see what works for you. Remember there is an insane amount of factors. 'Tone' is more or less perceived EQ. All of the following will add their own frequency curve:
-First, are you using a pick or your fingers, that will change EQ.
-Strings: Type, old v new might change EQ
-pickups, basses eternal electronics
-your cables
-whatever effect boxes, be they multi's or stomps
-the head (pre-amp, and pwr amp)
-the cab
-the mic (if mic'ing)
-how far the mic is from the cab
-the room (including furniture, people, etc)
-the humidity, wind shear, other environmental factors
-even your ear has it's own Freq. curve.
Layer all of those curves on top of each other and you get your end resulting 'tone'. In general you want to cut problem frequencies, rarely boost. You want to avoid over-manipulation. It's bad if say your pickups boost 300hz, pedal is cutting 300hz, your amp is boosting 300hz, your cab scoops it back out, the soundguy puts it back in, etc.
Also you should learn exactly what the knobs are doing. Ex. When you turn the 'low' knob on your amp, it's usually set at one frequency. Is it 40hz? 50? 100? Also how much cut/boost? If you turn it all the way down, it might be -10db, it might be -6db, or anything else. Add that the other knobs (mid, high, etc) might have completely different range of cut boost. Not to mention sweepable eq's. I know at least the ME-50b has a sweepable mid knob. This stuff can all usually be found in a devices manual under 'technical specs', as well as things like cabinet frequency responses, max db levels, etc.
Oh, and that reminds me, the Frequency curve of any of the items mentioned above might change if your playing at 60db or 100db, etc.
aren't EQ's fun? sorry for the long, irrelevant post. I have the day off and I'm bored.
