I've ruffled a few feathers with my statements about flats, and with some I've just flat out pissed them off.
Those that keep saying rounds can do what flats do, I agree...to some degree. But there is a difference between the two types of strings, each having their own character that the other can't do
as well.
DISCLAIMER: I play rounds and I know what they do, how they sound and how to use them. Some roundwound players like to play flats too, so a lot of my comments are not directed at those who already understand and appreciate what flats offer.
What I find humorous is that exclusively roundwound players think all they need to do is cut the highs, palm mute the strings, bump up the low mids or lows, maybe add a bit more compression, etc.
(I had to add the "etc" for those round players who will no doubt want to add their favorite "flat tone copping" technique I've missed, so therefore think I don't get how they do it) and end up with a Flat sound. They think of flats as "old school" thump and not much more. They certainly don't think flats are useful for anything other than a few songs at best.
What most roundwound players hate about flats is
the very thing flats excel at doing...and it's what most players hate doing...
blend into the rhythm section more. I said MORE, as in more than what rounds can do...not that rounds can't do it
at all.
For all their talk about being tight with the drummer, sitting down in the mix, or creating their own sonic space that they can accomplish just as easily with rounds
(it's all technique...everything is all about technique, isn't it? I mean that's why we all play washtub basses with one string...cause it's all technique...heaven forbid any of us would admit that we actually want or need certain kinds of gear to sound the way we do) they are also the same people who want to
cut through the mix and
be heard just as clear as the guitards. What I need is to NOT cut through the mix, but rather sit down lower in it, in my own space where the guitards can't go...just above the drums but also locked in with them
soundwise. Almost like giving the drums a note, where the drums provide the beat, but the bass makes those drumbeats play a musical note. It's all about sonic space for me. Roundwounds have a quality that makes them sound more guitar-like. But that is precisely what flats do for me...make my bass sound more like a bass and less like a guitar, which is not a very popular, 'modern' sentiment about bass.
The whole problem with rounds is that they make a bass sound like a lower tuned guitar and then bass players fight this "guitar sound" trying to not get lost with the guitars...and thus seeking all this gear to get themselves to cut through and be heard again. If you want your bass to sound like a lower tuned guitar, don't then complain that it gets lost in the mix with other guitars. What would you expect to happen? Not all roundwound players get lost in the mix, but given the thousands of posts over the years about that very problem, it's no surprise to me why it happens.
The whole point of this thread...my sole reason for posting it was my personal discovery of what flats do for me that
for 30 years I kept trying NOT to do. Have my bass sound like a bass and sit down in the mix as part of the low end, part of the rhythm section and NOT be a part of guitard world.
It's the very thing roundwound players hate about flats (I did too) that I found I needed! Now many roundwound players will tell me that, heck if all they wanted to do was get "lost in the mix" (another of my favorites), they can just as easily muddy up their sound to sound like flats.

They just do not get it. They mistake a bass sounding more like a bass and less like a guitar as just being "lost in the mix" and not "cutting through enough".
This discovery I made, about
me playing in
my band has nothing whatsoever to do with "cutting through the mix". It has everything to do with pulling back out of guitard world and getting back to the rhythm section where I (not you...
me) belong with the drummer. A place where the bass does rule (with authority) mostly because no other instrument sounds like it. I have no need to "cut through". I'm always present in the mix, because no matter what the guitards do, the bass is always clearly heard...as a bass. Flats do that better.