Regarding internal speakers, I have listened to several cheap to medium TVs on internal speakers, and yes on some models the sound was bad. But it doesn't matter, because the most mangled frequencies are high and low, and that's not the voice ones. When I listen on the TV with meh internal speakers I can clearly understand without any distortion voices in the normal TV programming, in sports TV, in old TV shows and old movies. The only offenders again are some of he new content.
So no, it's not the internal speakers who are at fault, at all.