Xperia z3 sound(speaker) related question, must answer. topic

Hello Guys,
How are u? I am fine. I am Kamlesh Jain from CHENNAI(INDIA). I am using Xperia z3 since 3weeks and the phone is very pretty and very good. I have one question, is: when we play any mp3's (via Walkman or via file manager), the speaker sound is pretty good but when the phone is ringing (when someone call to us) why speaker sound is low? So by my thinking there is a software setting inside the phone chip/inside the phone software and sound sets to low when ringing, that's the when phone ringing the sound is low and when we play any songs (via Walkman or via file manager) the sound is pretty good. I also have Xperia ZL, and the sound is very pretty for both Walkman and ringing. Friend's you can check this. So anybody have idea so how can we increase the sound when ringing???? Thank you Friends, please let me know......
I am using Sony ericsson>Sony since 15yrs. I am Sony lover.

Xperia Z3(CURRENT PHONE)
Xperia ZL
Xperia S
NEO
SATIO
SE C901
SE C902
SE C905
SE K850I
SE W960
SE W810I
SE K750
SE P1
SE P990I
SE P910I
SE P900
SE P800
SE P237
SE T610
SE T68I
SE T65
SE Z5
SE T29S
SE T18
AND I FORGOT FEW MODELS, WHEN I REMEMBER, I WILL MENTION