From Wikipedia...
The Who's live performances were traditionally extremely loud. For most of the 1970s and 1980s they were listed in the Guinness Book of World Records as the loudest Rock band in the world, measured at 130 decibels, though other bands, notably Deep Purple have since taken over that dubious honour. Daltrey has hearing problems as a result, and Townshend's later partial deafness and tinnitus is well known; popular legends hold that the members of the band suffered permanent hearing loss from their loud concerts, or that Townshend's right ear was damaged as a result of being too close to the drum kit when Moon detonated an oversized concussion bomb in it at the conclusion of a performance on the Smothers Brothers Comedy Hour in 1967. Townshend, however, maintains that the true cause was listening to music at high volume through headphones in the recording studio.