We timed to be at the 5/6 Thunderbolt at 11 a.m. on the way to the veterinarian.
At 11:03 I heard the compressor start up and run.
Horn was facing south - I was 90 degrees east of the horn.
I ran down the street and got to 55? degrees left of the mouth. Much louder.
Then ran north to 120 degrees from the front and the blower was more noticeable.
The horn rotated on previous occasions.
I shall e-mail the man who maintains Denver's sirens.