No names to protect the potentially innocent;
Imagine a prestigious event in a very large sports stadium. There are several sections to the entertainment, so lets assume that no permanent sound reinforcement structures can be erected. Into this place some kind of drumming band. The intention is for this band to play to a backing track in time. The audience of millions is supposed to hear this music seamlessly in time.
The speed of sound at in warm dry air is about 1140 feet per second. Since the distance between the center of the pitch and the closest audience is 150feet the band will hear the track 0.13 seconds late and the audience will perceive the band 0.26 second behind the beat.
I'm potentially a performer in the drumming band - should I panic?
All of your hundreds of drummers are on in ears listening to a click track. You have several channels available on your ears. One might be for the dancers, another for the Field marshals, and another for the horseback riders. Not only can they all hear the track in perfect time but Choreographers and stage managers can give you special instructions. All of the house PA is timed from the center of the pitch. The track for you group of drummers is also timed from the center of the pitch.
On the Beijing Opening Ceremony, we had 18,000 in ears on 6 channels.
Almost every performer had ears. see pictures HERE. http://www.bestaudio.com/2008_Beijing_olympics.htm
In 2000 at the Sydney Olympic Games was the first time for extremely large mass cast in ears. As a test we put out 300 ears on half the cast in a segment rehearsal. While waiting to start, the audio engineer rolled the track to check something with the pot down in the house - all of a sudden 300 kids started tapping in time to no apparent audio, it was a real defining moment.