Dial number: *#15963#*  to enter engineer mode. (Warning: Do not project model parameter adjustment disorder).   Choose “Audio”, “Normal Mode”, change the type to Sph, Figures adjusted to 160 maximum, after the point Set point ok to save, final turn the Level to Level 5,  click OK and restart the phone. (If the speaker can bear, can to try turn the Level 6).  According to the picture below: