Everyone who comes to Mass is a member of the main choir. Yes, there is a subset of parishioners who meet regularly to learn more difficult music offerings for Mass – a schola cantorum. But the main choir is the congregation.
When one listens to the best singing groups, no single voice is amplified over the others unless, of course, the music calls for a soloist, in which case the ensemble singers hold back in order to hear the soloist.
It is this exact same holding back phenomenon that occurs in congregational singing when we depend on hearing one voice amplified over the congregation and organ. We hold back, listening for the soloist instead of listening to the organ and the collective voice of the people.
Think about it… What happens when your favorite recording artist comes over the radio or whatever listening device you use? You join in singing! However, you hold back so you can hear the recording artist. If you don’t sing under the artist’s volume, you get ahead or behind in the song. Amplifying one voice over the congregation and organ causes a psychological phenomenon that leads to weak congregational singing: in order for the soloist to be heard, the organ must play softer than the amplified voice and the people must sing softer too – everyone must sing softer except for the amplified voice. This is a backwards way of practicing congregational singing.
Finally, our culture subconsciously recognizes that speaking or singing into a mic means, “Please be quiet! Listen to me. Please do not talk while I am addressing you over the PA system.” This is a subtle, though real message that is ingrained in our culture. This is why it is important to resist amplifying one voice over the congregation or organ.