A lion is capable of roaring up to 114 decibels, which is beyond the average threshold of human pain at 110 decibels. The vocal cords of most animals are triangular, whereas the lion's is square, which lets the tissues respond to incoming air more impressively.
In addition to the beneficial shape of their vocal cords, which allows greater emission of sound using less pressure, the strength of the tissue is greater. The square shape also allows the vocal cord tissue to withstand excessive stretching, which translates to much louder sounds without dilution. Researchers have determined that a lion's roar can be heard in excess of five miles away.