Arachin, Chapter 2, Mishnah 6. This chapter is built out of a long series of minimums and maximums, cases in which the halachah fixes a floor or a ceiling on a number. Our mishnah applies that pattern to the music of the Beit Hamikdash: what is the smallest choir of leviim that may sing there, and who is eligible to join it?
Twelve Leviim on the Platform
"Ein pochtin mishneim asar leviim omdim al haduchan": the choir may never be reduced below twelve leviim who stand upon the duchan. Their song accompanied the pouring of the nesachim, the wine libations that went with the korban tamid, and it was performed inside the azarah of the Beit Hamikdash.
The duchan was a raised platform that ran across the main courtyard, marking the boundary between the area where the people stood and the area the kohanim entered. On that platform stood the leviim who sang and the leviim who played the instruments.
Why is twelve the floor? The size of the choir was set to correspond to the number of leviim who played instruments each day in the Beit Hamikdash. That daily orchestra consisted of nine kinorot at a minimum, two nevalim, and a single set of cymbals, adding up to twelve players, and so twelve singers were required as well. The trumpeters do not enter this reckoning, because trumpets were sounded by kohanim and not by leviim. Flutes are also left out of the tally: they were sounded on only twelve days a year, so they had no place in the daily avodah.
"Umosifin ad l'olam": twelve is only the minimum. One may add to that number without limit, and as many additional leviim as wish to sing may join the choir.
The Minor Who Is Allowed In
As a rule, every avodah in the Beit Hamikdash had to be performed by adults, and the leviim counted here, both singers and instrumentalists, were adults. Our mishnah now records the single exception.
"Ein katan nichnas la'azarah la'avodah": a levi who has not yet reached bar mitzvah is barred from entering the azarah to carry out the tasks assigned to leviim, among them sweeping out the courtyard and shutting the gates. "Ela bish'ah shehaleviim omdim bashir": one moment alone is different, namely when the leviim take their places for the song. At that hour the boys who had not yet come of age were welcome to take part.
"Velo hayu omrim benevel uvechinor ela bapeh": they were not given instruments to play, neither nevel nor kinor, since at that age a boy is generally not yet at the level of skill demanded for performance in the Beit Hamikdash. They participated with their voices alone.
"Kedei liten tavel bane'imah": their purpose was to enrich the melody. A young boy sings in a high register, and when such voices were woven together with the deeper singing of the grown leviim, the result was a sweetness of harmony that the adult voices alone could not produce.
Rabbi Eliezer ben Yaakov: Present but Not Counted
"Rabbi Eliezer ben Yaakov omer: ein olin lamminyan": although the young boys are permitted to sing together with the adults, they are not counted toward the minimum of twelve who go up to sing.
"Ve'ein omdim al haduchan, ela ba'aretz hayu omdim": they were also not permitted to stand on the platform alongside the adult leviim. They stood on the ground below it.
"Vera'sheihen mibein ragleihem shel leviim": standing there, and looking up at the leviim raised above them on the duchan, their heads appeared to reach only to about the waist of the adult leviim, so that they seemed to be positioned between their legs.
"Vetzo'arei haleviim hayu nikra'im": these young singers were called the tormentors of the leviim. When the older leviim heard how sweet the voices of these boys were, they felt the pain of the comparison, and so the boys earned that name.