Many new devices are coming out with front facing speakers these days which really helps with the actual volume of your speakers. You no longer have to cup your hands around these devices to force the sound in your direction. On devices with back speakers you lose lots of sound as the sound is actually traveling away from your ears. There is a mod that will allow you to boost the volume on your LG G3. You will need to be rooted, you will need a file manager with root, and you will need a text editor. There is a particular file that you will need to modify. Once modified you will notice a pretty big difference in the LG G3's volume. Head to the link below for full instructions.
via XDA