Numbers 10:3

ותקעו בהן WHEN THEY BLOW WITH THEM — with both of them; and this (protracted sound, a “Tekiah” on both trumpets) is the signal for summoning the congregation, as it is said here, “then all the congregation shall assemble unto thee at the entrance of the tent of meeting”.

וְתָקְע֖וּ בָּהֵ֑ן וְנֽוֹעֲד֤וּ אֵלֶ֙יךָ֙ כׇּל־הָ֣עֵדָ֔ה אֶל־פֶּ֖תַח אֹ֥הֶל מוֹעֵֽד׃

And when they shall blow with them, all the assembly shall assemble themselves to thee at the door of the Tent of Meeting.