Smile Sony Xperia Z's calling speaker located above the touch screen of the phone question

Hello, i want the sony xperia z only for making good loud calls.

So, i wanted to know the quality of the front facing speaker which is located at the very top of the phone near and above the front facing video calling camera. It is also located above the touch screen of the xperia Z.

Ok so thats the speaker im talking about NOT the one on the side of the device for playing music etc.....

So how is the one above the screen's noise. is it clear and loud for my ear to hear the person im speaking with privately without sound going to the public. The speaker should be adjustable. Is it or not?
Thanks very much