Quite a few Sony Xperia Z owners have expressed disappointment with the low sound quality, or at least volume, of the device’s external speaker—an issue that may stem from the speaker’s water resistance or its small size. Nevertheless, XDA Senior Member ZeroInfinity has managed to increase both the internal and external sound volume with the Extra Volume Boost mod. A normal version is available for devices running AOSP-based ROMs, while users of Sony’s stock firmware will be able to enjoy either the normal or the ‘Super-loud’ version.
Installation is simple, requiring users to download the zip file of choice and flash it through a custom recovery such as CWM or TWRP. It is, however, recommended to make a Nandroid backup first just in case the mod either doesn’t work or causes issues such as no sound, which one user reported. Flashable zip files are also provided for those who would like to revert the effects of the mod.
Please keep in mind that playing sounds at high volumes for extended periods of time may damage the external speakers since they are being taxed to a greater extend than with the original settings. For more information and download, visit the original thread.