Is it possible to turn up the volume past the maximum? I recall in Loki, you were able to do that easily by opening the sound panel. In Juno, the option is no longer there.
The command for that is
gsettings set io.elementary.desktop.wingpanel.sound max-volume 150. You may need to log out for this to take effect.
Also take into account that this is going to cause distortion since it's going to increase the volume over 100%.