RBC Center apparently makes a claim of having the record at 134 dB.
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According to The Hockey News, an unofficial reading of 134 decibels was measured during Game 7 of the 2006 Stanley Cup Finals against the Edmonton Oilers. It is the loudest reading ever at an American sporting event.
http://en.wikipedia.org/wiki/RBC_Center
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Some quick research says the pain threshold is usually defined at 120-130, but that level can be painful for some or awesome for others. If that's true I'd say Allen Fieldhouse is probably sitting around that 130 mark at it's loudest.