My horn sounds different

If you have ever heard a Cadillac horn on an older Deville, they are loud and very powerful. Recently, my horn is not loud and the sound is different. This may not make sense, but if horns were male and female, it sounds like a female horn! It' is just weak, not as loud and has lost its big powerful sound. Any ideas what may be wrong? Do you know how I can make my alarm go off so I can hear if the horn is working properly when the alarm goes off? Thank you.