Miui 8 Low Sound Fix it is very simple.

Is the speaker volume  your phone is very low ?

You can increase the speaker volume yourself, it is very simple.

Step 1 - Put Your Engineer Cap On

In your phone app, and dial *#*#3646633#*#* to enter MTK Engineer Mode. Go to Hardware Testing and choose Audio.

Step 2 - Understand the Formulae

Loudspeaker Mode - Rear Speaker for Media and "Speaker Mode" for calls

Value is "160" set

Max vol. "145" set

Good luck!