32. The nature of the “presidential” parts requires that they be spoken in a loud and clear voice and that everyone listen to them attentively.[Musicam Sacram 14] Therefore, while the Priest is pronouncing them, there should be no other prayers or singing, and the organ or other musical instruments should be silent.
33. For the Priest, as the one who presides, expresses prayers in the name of the Church and of the assembled community; but at times he prays only in his own name, asking that he may exercise his ministry with greater attention and devotion. Prayers of this kind, which occur before the reading of the Gospel, at the Preparation of the Gifts, and also before and after the Communion of the Priest, are said quietly.
The prayers at Mass are important enough to be rendered without distraction. GIRM 32 in suggesting a “clear” voice, is telling us that intelligibility is important. Do most clergy know they must cater their speaking style to the building in which they celebrate Mass?
A note on the 2011 “upgrade” for GIRM 33. The priest in 2000, was instructed to say these prayers “in his own name” inaudibly. In the 2011 update, “quietly.” The Latin original is secreto.