[igcogsus] Singing disruption

The human voice can be quite loud if trained: opera singer.  The human ear has evolved to be particularly sensitive to human voice.  Synchronized voices, a chorus, can be even more powerful because of constructive interference (maybe? or some other psychoacoustic effect).

Use a singer, or chorus, to create a loud sound, to convey a message, in a setting where other forms of amplification are not possible.

One application is to disrupt an opponent's political rally.  A singer carries no megaphone nor vuvuzela to confiscate, wears no distinguishing T-shirt to be stopped at the door.  A chorus thus smuggles itself in, disperses themselves invisibly among the crowd, and suddenly starts singing on a synchronized signal.

Even afterwards, with ventriloquism and acting, it may be extremely difficult to distinguish who the disrupters were (and they carry no physical evidence as already mentioned).

What ratio of singers is needed to overpower the untrained voices of the crowd shouting back upset at the disruption?  How many singers do you need to overpower a public address system?  I'm guessing these numbers are quite small.