All I gotta say is AIR HORNS!!!
Got a pair of 'em on my '81 GL1100 and I have "scared" more than my fair share of NY drivers back into their lanes or gotten their attention...
Still have the stock horns out in front of the fairing, but added a 30 Amp relay to the horn circuit which is directly connected to the battery for maximum voltage, and now controls the compressor for the air horns... for a short "blip" of the horn, the stock ones are fine (like giving your admiration to a pretty girl on the street) but hold down the horn button for more than 1/2 second and the air horns are making your presence known..
I used to have the air horns running through the horn switch, until I noticed the switch was melting from the excessive current draw of the compressor... so the switch now only controls the high power relay which powers both sets of horns... much safer for the horn button....
I don't have the covers on the horns, so every once and a while I pull off the air hose and send a little WD-40 through them to keep the diaphragms clean and free of road grime (after the WD-40 I either use the compressor in my garage, to blow it through, or just lay on the horn button for about 10 seconds or so)
The horns originally came from one of my many boats, and were a little pitted so I had tried to polish them up and wound up removing almost all the chrome from the horn bells, and getting nice polished brass... I may still powder coat them in sliver...
Here is one of them (left side of bike) pictured below:
Sound pressure levels for both the air horns AND the stock horns all going at the same time measured at about 135db at 5 feet!! That's friggin' LOUD!!!
Rich