I changed the horns out for a more robust version that Feature steel housing and plastic projector, can be mounted singly or as duals (I highly recommend a high and a low dual install) at 130 dB:
FIAMM 72112 Low Note (420hz) Freeway Blaster Horn
http://www.fiamm.com/Horns-F-Freeway-Blaster-Low-Note-Zone-21-typeLBU84L117A127-Prod-956-561
FIAMM 72102 High Note (500hz) Freeway Blaster Horn
http://www.fiamm.com/Horns-E-Freeway-Blaster-High-Note-Zone-21-typeLBU84L117A127-Prod-957-561
Many people are happy with the compact "El Grande" model (frequency
405-485):
http://www.fiamm.com/Horns-El-Grande-Twin---P-N-74100-Twin-Electric-Horns-Zone-21-typeLBU84L110A127-Prod-997-561
It's super easy to do. Just remove the plastic cover over the radiator (pop the center plastic pins in to loosen the fasteners). Page 356 in the owner's manual tells you how to remove the motor compartment cover. Then remove the two 12mm hex head bolts that hold the radiator in.
Remove the top radiator brackets (they just slide up, off the radiator) and push the radiator assembly towards the windshield. You'll see the two horns on the driver's side, mounted high, in front of the radiator. You'll need a 12mm hex head wrench to remove the hangars. If you want to "go for it", just remove the 10mm hex head nuts from the center of the horn and reuse the hangars.
Don't drop any bolts or nuts because you will have to remove the lower motor cover from the bottom of the car to retrieve them. It's not hard, but you have to crawl under the car with a 10mm socket and short extension, and a flat screw driver.
Pictured is the stock Low tone horn (420 hz) with the replacement Fiamm horn. The high tone horn looks the same (500 hz), but is not pictured: