Diagnosis
This is a dynamic range issue. The soundbar is receiving a compressed audio signal (like Dolby Digital) but isn't processing it to boost center-channel dialogue.
How to Fix It
Enable Night Mode or Voice Enhancement. Press the 'Gear' button on the remote. Use the volume buttons to scroll to 'Sound Mode'. Press 'Volume Up' to select. Scroll to 'Night' or 'Voice' and select it. Night Mode compresses the dynamic range. Voice Enhancement boosts the mid-frequencies.
If That Didn't Work
Check your TV's audio output format. In the TV's sound settings, change the Digital Output Format from 'Bitstream' or 'Auto' to 'PCM'. This sends a simpler signal the soundbar can handle better for dialogue.
Heads Up
The B650 does not have discrete center channel speakers. All dialogue enhancement is digital processing. It will not be as effective as a true 5.1 or higher system with a dedicated center.