The position of the elders was not of the same rank as that of Moses, for he was the king of Israel, and it was for this reason that God had bidden him to secure trumpets, to use them for the calling of the assembly, that this instrument might be blown before him as before a king. Hence shortly before Moses' death these trumpets were recalled from use, for his successor Joshua did not inherit from him either his kingly dignity or these royal insignia. Not until David's time were the trumpets used again which Moses had fashioned in the desert.
God Gave Moses Silver Trumpets as Symbols of Kingship
Legends of the Jews 4:68