One afternoon in the summer of 1969, Woodstock promoter Michael Lang took sound engineer Bill Hanley to Max Yasgur’s farm in Bethel, N.Y., to show him the grounds for the concert he was planning. The moment Hanley looked out at 700 acres of grassy hillside, he knew the only way to throw sound that far was to build a system from scratch. Soon, two towers of yellow construction scaffolding rose 70 feet in the air, each cradling two clusters of speaker cabinets. The cabinets were 6 feet high, 7 feet wide and weighed half a ton each. Hanley had stuffed each of them with four quads of 15-inch speakers—D130s, they were called, made by a California company called JBL.