Numbers 10:2-4

2Make thee two trumpets of silver; of beaten work shalt thou make them; and they shall serve for the calling together of the assembly, and for the journeying of the camps.

3And when they shall blow with them, the whole assembly shall gather to thee at the entrance of the tent of meeting.

4And if they blow with one, then the princes, the heads of the thousands of Israel, shall gather unto thee.