Wow... that takes me back...
Here in Cleveland, you used to be able to go across town to the Cleveland Orchestra's concert hall (Severance Hall) about this time every year- and join the orchestra and the Chamber Choir to sing selections from the Messiah, including the 'Hallelujah' Chorus. You would walk in, buy a copy of the score if you didn't already have one, and they would seat you according to your voice. You can't believe what a rush it is to hear the whole concert hall full of people singing this music! I managed to make it to a few of them... good memories!