One of the common complaints we are hearing from early adopters of the Xperia Z2 is that the ringtone volume for incoming calls is very low. However, there is perhaps a simple reason for this – Sony has only activated the bottom speaker for incoming ringtones rather than using the top speaker too according to reports.
This also appears to be the case for calls conducted via speakerphone too. Sounds like an odd decision to only enable one speaker, when arguably you want your phone to be as loud as possible when receiving calls. Hopefully this is a simple firmware fix for Sony though.