This module enables the earpiece to be used as a secondary speaker while playing music or videos.
There were a few modifications in the mixer file, similar to Oneplus 5 & 5T.
*I am not responsible for any damage to your device*
You will need a stock rom with Magisk installed.
Just add the module in magisk & reboot.
If you want it to be more loud, flash the cleanslate kernel and increase the earpiece gain.(*At your own risk)
v8 : Releases
Source : Github
Note : Download the file in the attachment, extract it & move it to ViPER4Android/Kernel folder in internal storage and select TubeAmplifier file in Convolver. This will significantly boost the output of both the speakers without causing any distortions. [Original thread]
Addidional Note : As reported by aenews v8 breaks AML compatibility with other mods, so if you're facing the same issues please revert to v7!
OLD VERSIONS :
Youtube Video :
Featured On XDA Portal
v1 - Initial Release v2 - Fixed the earpiece not working in several apps. The mod is now standalone and works without Viper as well v3 - Fixed the earpiece not working during call v4 - Fixed Bluetooth Audio[PIE] v5 - Right channel audio plays through both the speakers now. Earpiece gain increased by 2dB v6 - Fixed latency issue between earpiece and main speaker v7 - Mod is now AML compatible v8 - Fixed the issues with speakerphone and bluetooth devices
I had to go through several threads in order to port this mod.