Recently, I installed the Stebel Nautilus compact air horn. It is incredibly loud, based on my garage test. In my garage, it sounds like a train is coming. Now we're talking. The Stebel compact air horn does fit in an R1150R, but it is snug. It is a tight fit, and the fork hits it when you turn the bars all the way to one side. You need to use a relay to wire it. I put the relay inside the fuse box. I also added an in-line fuse. I used 14 ga. wire for the installation.
There is no delay between pressing the button and hearing the horn. I guess that because of its compact size, it does not take a noticable amount of time to build up air pressure.
While the horn sounds really loud in the garage, it is not quite as loud as I hoped on the road. It is definitely a loud horn, and it gets people's attention, but it is not the tractor trailer horn sound that I am longing for. It does have a European sound that is appropriate for this bike, whereas the FIAMM sounded more like an old Buick.
Here are some pictures. I apologize for the poor quality. I took them outside at night time, and they are a bit blurry.
This shows that I mounted them in the same place as the stock horn.

At the bottom of this picture, you can see that I wrapped the wiring in spiral plastic wrap. I drilled a hole in the side of the fuse box for the wires to enter.

With the fuse box lid removed, you can see that I put the relay and the fuse holder in the empty spot in the fuse box.

All connection were soldered. I used marine grade heat shrink tubing wherever possible to cover the soldered connections.










