Unearthly choir

Unearthly choir was an evocation spell cast cooperatively by three or more priests in which they sing a dissonant chord for possibly devastating effect.

Effects
Three or more priests were required to cast this spell simultaneously and they had to be within 10 ft (3 m) of each other at the time of casting. Unearthly choir took only half a minute to cast and at the conclusion all the priests involved each sang a purposefully discordant note that combined into a cone of sonic power aimed at their enemies. The more casters added their voice to this spell, the greater the effect.
 * Trio : Three casters created a cone 120 ft (36.6 m) long and 40 ft (12.2 m) wide at the far end. Those caught in the cone of sound could resist the spell and take less damage, but undead were particularly susceptible.
 * Quartet : Four priests created the same sized cone and did the same damage as a trio but deafened for one minute all those that did not resist the spell. Undead creatures were not able to resist the spell at this level of power or higher.
 * Quintet : With five voices, the damage was half again that of a trio and all were deafened whether they resisted the spell or not. The sonic vibrations were strong enough to shatter fragile items like pottery, glassware, or crystal.
 * Ensemble : With six to ten voices joining in, the cone was extended to 180 ft (55 m) and 60 ft (18.3 m) wide at the base. All creatures in the area of effect suffered three to five times the damage that a trio could put out, were deafened for a few minutes, and non-magical items made of wood or bone, such as doors, chests, furniture, etc., had a good chance to shatter or splinter.
 * Choir : Eleven or more priests could create a truly devastating effect in a cone 300 ft (91.4 m) long and 100 ft (30.5 m) wide. All normal items were instantly shattered and structures were hit with the force of a catapult. All creatures in the area were deafened for at least a few minutes and suffered up to ten times the damage put out by a trio. Low level undead (skeletons, zombies, ghouls, wights and the like) were obliterated.

Components
This spell only required a verbal component to cast, albeit from at least three casters.