"How big an amp do you think you need?"
I get asked that question all the time but being naturally well indow...... Sorry I didn't understand the question. ......... How big is your car?
With bass it's the watts you don't use that are important. It takes quite a bit of power/watts to reproduce a nice fat, clean signal thru a good sturdy speaker in a well made speaker cabinet. Then taking that signal so it can be heard over top of guitars, which can get away with a lot less watts and drums, not to mention drummers. Then you factor in the type of music you've chosen to play. Metal=lots, Jazz=less.
So if you have a bass amp that says 500 watts, your first 100 watts are super clean. But when you get into 1/2-way the 250 watt range your amp is working harder and sounds different, even if you don't hear it. More expensive amps can take more because they a true watts. Remember, like everything, you get what you pay for.
In the old days lots of watts meant lots of weight, the power wattage came from the transformer. Now with the modern switching systems in amps 500 watts can weight 10-lbs.
So if your pushing you amp past half way, volume wise, you don't have enough wattage. If you have two volumes your power amp can be at 3/4 and you pre-amp at 4 or 5 and that's where the amp likes to be at max volume.
After that, as Scotty said; "I'm afraid she's breaking up Captain."