Matthew Poole and continuators on Numbers 10:2

2 Make thee two trumpets of silver : of an whole piece shalt thou make them, that thou mayest use them for the calling of the assembly: and for the journeying of the camps.

For Aarons two Sons: though afterwards the number of the trumpets was much increased, as the number of the Priests also was. See 2 Chron. 5. 12. These trumpets were ordained, both for signification of the great duty of Ministers, to wit, to preach the word; and for use, as here follows.

A metal pure and pretious, and giving a clear sound.

See Exod. 25. 31. Numb. 8. 4.