To provide the best audio to complement the pictures, your TV should be hooked up to a separate audio system, be it soundbar or home cinema separates, but this isn't always an option. So, here's what we listen for when testing a TV's speakers:
Bass: Deep, rounded rumbles that don't cause the set to rattle or speakers to distort cramp or overwhelm the rest of the sound; but that expand when needed.
Vocals: Voices should sound open, rich and clear, not boxed in, nasal or thin.
Trebles: Treble effects should sound clean, rounded and smooth in loud scenes and shouldn't dominate the soundstage.
Soundstage width/depth: A good TV should throw the sound away from the TV, to the sides, forward and back, to give an extra dimension to what's on screen, without losing any coherence.