If we are using bards to hearld the call and bulster the troop as we run off why not:
The army/general/group being attacked has thier bard sound the horn call first. When the two closest hear it, they repeat the call. Then the next group to hear it repeat it sending it further out and so forth = a wave of inspriation and guidance
I say guidance because each army/group will have it's own blast or calling. Any variety of a short series of blasts or a short set up of notes, as there are enough variations even with a simple horn for five seconds worth of blasting to have each with thier own call.
Going on however, the distinctive call that starts it will be repeated by the others as it goes around and outward. As the sound travels it will give inspiration to allies and tell us specifically who needs help and knwoing the battle plan where that group is most likely. It may still take a round or two or three to get everyone to the right place, but once in the general area it should be fairly noticable as to what the bad evil threat is. If it is enough to get all of us together it should be significant enough to notice when right there.
Also once all the horns are going it has to have similar noise/effect as that of the huge horn except bad evil things will not be able to simply hit one target to make it stop.
ipes of Sounding: When played by a character who has the Perform (wind instruments) skill, these pipes create a variety of sounds. The figment sounds are the equivalent of ghost sound (caster level 2nd).
