Another obvious thread, but a good chance to tell some stories.
This one might seem like a no-brainer, but the loudest show I've seen was Motorhead back in '99. The venue held about 1000 people, I guess. And I wisely stood toward the back. As usual, I had earplugs in...but at one point I thought "I wonder how crazy loud it is without these". So I pulled one of them out for a few seconds.
What followed was something I'd never experienced before, or since. I literally could feel the sound MOVE past my ear like a stiff breeze. I'm not even exaggerating for effect - I could FEEL it.
That earplug went back into my ear REAL fast.
As far as bands you might not expect to find in this category, I remember seeing Black Rebel Motorcycle Club on the tour for their debut album at the Hurricane ( now The Riot Room ) here in KC. It's your standard 300-ish capacity club, but they were cranked up to borderline arena-level volume. It was RIDICULOUS. Good show, but stupid loud.
At the small concert venue The Newport (formerly known as The Agora) In Columbus I saw Brother Cain and Candlebox. Loud show, but I enjoyed it.
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Get the idea cross around the track Underneath the flank of thoroughbred racing chasers. Getting the feel as a river flows. Would you like to go 'n shoot the mountain masses?