I've always used cabs without tweeters. I predominently play mustang basses with stainless flats, so I'm not expecting anything particularly shrill to come out of my amp.
My amp is a lovely Ashdown ABM600 Evo IV. I keep this at the guitarist's studio where we rehearse and I use the cabs he already had in the studio - an Ashdown ABM 115 with an ABM210 with tweeter on top (in portrait mode rather than landscape if you get the drift. I'm not sure what generation the cabs are, but they're probably at least ten years old. I kind of recall switching the tweeter off on the 210 when I first set it up, but at the rehearsal this week the bass rig was hissing very noticably, so I'm guessing the tweeter switch got knocked back to 'on' when the cab was in transit from the last gig.
The thing is that I have rejigged my pedalboard and at the beginning of the rehearsal and spent some time adjusting the eq on the amp which resulted in a slight bass cut and a slight boost to the mids. I'm pretty sure I kept the treble roughly flat. Listening back to the recording of the rehearsal confirms that the bass tone was the best I've had in living memory but the hiss was very noticable. i think the slight bass cut removed some mud and adding mids added clarity. I also had the volume a bit higher than usual which enabled me to play (fingerstyle) with a lighter touch.
We're rehearsing again on Monday and I'll try to keep the same settings but check the tweeter switch and A/B with it on/off.
Will switching it off take away some of what I liked so much about the tone I got this week? or should the tweeter only really concern itself with the very high slappity thwackity frequency range which would be absent from my signal?
I'll report back with my findings next week, but I'd be interested in what others think about this.