Mosiah 2
I would bet that king Benjamin not only built a tower but also used something to amplify his voice, such as a megaphone. If the people then sat in their tents with the doors facing the tower then their tents would dampen noise coming from anywhere other than the tower.
When Benjamin is speaking of men who have transgressed and chosen to follow the adversary he is speaking to a people who have already been blessed with the gospel – not to those who are ignorant. Therefore they do not have the option to receive their highest possible degree of exaltation by accepting their Savior after they die. If they so die they must endure the torments of damnation until they are resurrected.