This mod will boost the maximum volume of your phone. It is unknown if this will cause any damage to your device to run it at full volume but it may cause hearing loss if its up next to your head. Root is not required for this.
Dialer *#*#197328640#*#*
[5] AUDIO
[1] HANDSET
[1] VOLUME
[1] SRC Speech RX Volume
[5]5_lvl : 88
Menu -> Key Input
Change to 100
OK
Press back to save.