There are separate microphones in N9 for normal (earpiece) mode and for loudspeaker mode, so that is explaining why the mic is working in one mode, but not in the other.

The normal mic is located behind the bottom grill of the loudspeaker. The mic used in the loudspeaker mode is located next to the camera flash.

So if the the mic is not working at all in loudspeaker mode calls, the secondary mic can really be broken. Of course, some mess-up with the SW can still possibly explain the problems.

Have you applied any (audio) tweaks for your N9? Just pondering if something could have messed-up some audio setting files etc...