On this date in 1972, Deep Purple, named the loudest band by 'The Guinness Book of World Records', received a gold record for 'Machine Head'.
And how did Deep Purple come to be named "loudest band" by 'The Guinness Book of World Records?' Well the story goes that at their performance at London’s 3,000-seat Rainbow Theater in 1972, the volume clocked in at 117 dBs and the intense pressure of sound that loud in an enclosed space knocked three fans unconscious! So they say, anyway.
According to guitar maker Gibson's website "Any volume measured at more than 85 decibels (dB) is considered dangerous and can potentially cause hearing loss or damage, like the permanent ringing known as tinnitus." By the way 'The Guinness Book of World Records' no longer has a "loudest band" designation so as to not encourage hearing damage.
See gibson.com's list of 'The 10 Loudest Rock Bands of All Time here.