I was a tour guide that day for the War College. All Colonels and Generals. I took them to the pad and we were about 5 miles away during launch. The sound was enormous and reached 120 DB over 20 miles away, so you knew what we were going through. It knocked my hat off and nearly floored me.
This was the most awesome sound I had ever heard.
I later heard that it was equivalent to a sustained 0.6 - 0.8 Kiloton explosion where we were.