I have a problem with motorcycle horns in general and that problem is that they don't sound like car horns. They're cheap little, disc-type "beep-beep" horns that sound like anything other than what you'd expect to hear coming a full sized vehicle. It's not necessarily an issue of decibels at all. On the contrary, the factory horn on my new Versys 1000 seems pretty loud enough. It's just the wrong sound.
I've been riding for well over 40 years and I've come to the conclusion that people in automobiles simply do not respond (or respond fast enough) to sounds that they're not accustomed to. It's made me wonder when after so many times I've laid on regular motorcycle horns to alert a driver dangerously crossing into my lane ... and they just roll right on over ... and then look surprised to see you averting the accident that they almost caused.
What I've done now for several generations of my cycles is replace the factory horn with a decent aftermarket horn that sounds like a car horn. The last two horns that I purchased were Fiamm Low Tone Freeway Blaster horns. The blaster part is somewhat of a misnomer; they're loud, but not crazy loud. Plus they run around $15-$20; very reasonable for the safety.
My normal shop for stuff like this is Pep Boys, but unfortunately they don't carry the Fiamm model anymore. They have a new brand called Blazer Highway Blaster Horn that comes in two tones (high and low) and three decibel levels. I picked up the low tone, which best sounds like a car horn, and the highest of the three decibel levels for the 2015 Versys 1000 LT.
It's definitely a big sucker compared to my factory disc horn but the horns are tucked up in the nose of the motorcycle and there's a fairly large cavity there to accomdate a larger model.
Like all these horns, the wiring is non-polarity conscious, so the two lead wires attach to either mounts without regard to positive or negative. The only real issues are situating the horn so it does not interfer with any working parts and is protected from the elements as best as can be accomplished (e.g. point horn down so it won't collect rain water).
As far as working-part interference, the horn location is in line with the turning operation of the forks coming from both directions. Fortunately, using the mount that came with the Blazer (removing the factory mount bracket) and the threaded hole that was used for the factory mount, the Blazer sat perfectly between the two forks as they turned right and left. In addition, the larger horn tucks up mostly behind the nose making it nearly invisible.
So, the last question was, how did it work and sound?
Well, the answer is okay. The low note absolutely sounds like a car horn, which is what I'd wanted. However, I do not believe that it's as loud as the Fiamm Blaster models I've had in the past. This particular horn (the loudest of 3 models) is supposed to throw off 132 decibels, which is more than the Fiamm's 130 decibels. Having purchased the loudest, I supposed I was naturally expecting to at least vibrate some windows in the neighborhood. Far from it.
Ultimately, the Blazer Horn will probably work out, but I'm going to keep the jury out for a couple weeks and see how it grows on me ... I use my horn alot. :)