myth busted...
The original horn on our 1995 OBS Ford F150 finally gave out and I was trying to to decide on what to get when I came across dozens of listings for air/train horns on amazon. I have installed quite a few of these over the years but was shocked at how cheap they have gotten. But they claim 150 decibels and while they're loud - I don't think it's quite that much - but we can test!
Since I live in a state that has vehicle inspections, the horns need to still sound like a regular 12v vehicle horn - I think the dual horn setup sounds like a really loud automotive horn crossed with a tiny train.
www.amazon.com/Trumpet-Compre...
If you're going for the deepest and loudest tone possible I recommend the longer single version of this horn.
www.amazon.com/Trumpet-Compre...
My testing found that it only produced 111.9 decibels and even with the hood open we only got 129. So it really doesn't seem possible to achieve the advertised 150 decibel rating unless your inside the horn itself. They are substantially louder than the factory horns and have a better tone. So in the end I'm still glad I did it for $26.