Numbers 10:2-4

2“Make yourself two trumpets of silver, of hammered work you shall make them; and you shall use them for 1summoning the congregation and for having the camps set out.

32When both are blown, all the congregation shall gather themselves to you at the doorway of the tent of meeting.

4Yet if only one is blown, then the 3leaders, the heads of the 4divisions of Israel, shall assemble before you.