Yes, they are. According to the older Federal Signal catalogs from the 1970s, they say that the STL-10 has better penetration in hilly and mountainous areas. Also, to distinguish between other high-pitch sirens that might be in the same area.pyramid head wrote:I do not know where I read this, but I think somebody said that STL-10's were made for mountainous area's, and the low tone is for penetration. Is this correct?