I haven’t really seen this explained from a technical standpoint, so here goes. Someone correct me if any of this is wrong.
Most movies are mixed in a higher-quality format that has lots of different channels of sound. Left, right, center, surrounds, top surrounds, subwoofer, etc. Most dialogue is placed heavily in the center channel so that it can be right in your face.
If you’re watching on a TV, or even certain types of sound bars that can’t decode the available audio format, then the sound is getting “down mixed” to 2-channel stereo – left/right. The dialogue is then washed out and lost in the mix. There are some TV’s that do a “dialogue boost” or similar, but YMMV with that.
The best solution is to look at a nicer sound bar that will handle most high-quality audio streams – DTS, TrueHD, Atmos, etc. Let it run the configuration setup where it measures your room, etc. Even better would be to invest in a basic 5.1 system, but you’re looking at a pretty decent chunk of change to do that, along with a lot of added complexity.
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