"In these horns there is a reed that vibrates against the diaphram (the square metal part) when voltage it applied to it, which makes the noise; it depends on how much juice it's getting and the way it hits, etc. With these there can be a tiny variation in each horn (not even enough to be measured.) That it my guess. All I care is that they work." I saw this message at the video... "Simplex 4005 System Test"

How about on electromechanical or mechanical horns?