How does head tension affect the banjo's sound?

Tom Nechville demonstrates how even a slight difference in head tension can affect the banjo's sound. Time links below. Played on a mahogany Renaissance Vintage w/ Hybrid tone ring, a lightweight banjo coming in at just under 8 pounds.

Head tension @ 94 on drum dial: 1:44
Head tension @ 93 on drum dial: 3:42