If the device is rooted and has custom recovery, try this:
You can also use root explorer to browse to the file that handles the devices audio input/output/volume parameters(what it is called and where it is located in your system partition is/can be different from one device brand or android version to another), then open that file in a note editor and change the values manually then save the file and reboot. Start with very small changes, then increase as needed, this way you get an understanding of how much increase gets how much result without going too far and damaging your hardware.
Sent from my LGL84VL using Tapatalk
Thanks for the response, but I would rather not do anything that involves rooting the device.