Back in the day with CRTs and projection screens, the TV would be pretty big regardless. They didn't have to worry about bundling in some nice speakers with a TV, because hey the TV is going to be quite large and that cavity can be a nice resonance chamber if done right.
Now, all TVs need to be super thin which can be a nice thing don't get me wrong. But their packaging means their speakers are often very compromised. Sure, they're OK in a pinch, but even a cheap sound bar will often out perform most TV's built in speakers. So unless you're using the TV in a space where you just don't care about the sound quality, you'll get a lot out from having at least a sound bar or some other external speaker setup.
This basically adds more bass and treble as you lower the volume, due to the way the ear works - the Fletcher Munson curve.
This still won't help with the terrible excess dynamic range that current movies insist on doing though.
You'll still have to adjust the volume all the time, but it will make things sound much better at lower volumes.
aformat=channel_layouts=stereo, compand=0 0:1 1:-90/-900 -70/-70 -30/-9 0/-3:6:0:0:0Speech reproduction gets muddled by distortion and by masking ( https://en.wikipedia.org/wiki/Auditory_masking ).
If you have one speaker reproducing both speech and other sound, this is what happens:
1. additional sound output means heightened distortion
2. when two sounds come from two places, our brains can separate them due to phase differences and spatial perception, so those two sounds mask each other less than if the same two sounds come out of a single speaker, even if it's perfect, with no distortion etc
3. the speaker is made for broad range reproduction and not voice reproduction, so it'll de-emphasize speech frequencies, which are exactly those frequencies that also make music sound like it's coming out of a cardboard box. ultimately the applied eq (equalizer) curve will create speech that's slightly muddy, like someone talking from behind a blanket.
4. sound bars use tiny transducers which are woefully underpowered compared to the SPL (sound pressure level) they're tasked with producing. This is done by using multi-band compression and limiting. This sometimes creates situations where the limiting might be recovering after a slightly louder sound, and the very next syllable will be muted.
However, having a dedicated speaker for the center channel is none the less way better than not having one at all. If that's all you can try, you can try your luck. But be aware that getting a cheap one will probably not get you where you want to be - you'll have to spend a pretty penny. At that point if you have the space you might want to get a 3.1 bookshelf speaker setup. They don't have to be very large to provide great value-for-space-used.