Also, since nobody has mentioned it in this thread, are you aiming the speakers away from the building and firing outward, or are they firing toward the building? The latter is a much more efficient way to make sure the level is adequate and won't disturb people in nearby buildings. In addition, the sound reflecting from the building reinforces what's coming from the speakers, so it may be possible to cover the whole area better AND achieve a high SPL. Firing from the building is just being a glutton for punishment and requires a lot more power.