The horns are mounted with the shorter horn on top and the longer horn on the bottom. Each air horn is pointing down slightly. This will allow any water which enters the horn to easily drain out, keeping the horns functioning for a long time.
Here is a close up of the top mount. You can see a bracket mounted to the frame. It has two bends in it. I used rubber grommets and bushings to mount it to a hole which was already in the frame under the tank. You can't tell by this picture, but I polished the aluminum with Mother's Mag and Aluminum polish. It looks like Chrome! You can also see the helmet lock which I relocated here also.
This is a close up showing the lower mount and the compressor. The lower horn mount is a straight piece of aluminum mounted to one of the frame bolts. If you look closely, you can see how the compressor is mounted both with a straight piece of aluminum and an 'airplane' clamp. It is hard to see all the details because I painted the compressor and straps black to help them to blend into the bike to help to hide it.
I was very unimpressed with the horn on my Aero. I know that almost all motorcycles come with a horn, but most of them can barely be heard. I went down to my local auto parts store and purchased a set of air horns manufactured by Wolo for about $39. They come with two black horns, an air compressor, a horn relay and some tubing. If you prefer, they also have a pair of chrome horns. The black horns are supposed to be a lower pitch, I thought they would help to make my bike sound "bigger". I also purchased a few feet of 3/4 x 1/8 inch aluminum bar from a local hardware store.
Using the aluminum bar, I made a bracket which mounts between the front engine mount and a point on the frame under the tank. I used a rubber bushing at the upper mounting point to isolate some of the vibration from the engine. I made two bends and drilled a four holes to mount the bar and the horns in the aluminum bracket. Then I polished the bracket with some Mother's aluminum and chrome polish. I mounted the compressor with another piece of the aluminum bar to the same bracket which holds on the factory horn. I also used a stainless steel hose clamp to strap the compressor to the frame underneath the radiator.
The engine on the Aero vibrates a lot and will cause premature failure of the horns and bracket if you fasten the bracket to the engine or mount the compressor so it is not supported well. I know this from experience!
I mounted the horn relay in the white connector box which is under the tank. The horn relay was wired to the factory horn and also directly to the battery through a fuse. I left the factory horn connected and functional as a back up in case the air horn ever failed. Be sure to route the tubing away from the exhaust pipes and fasten them with some nylon ties to the frame of the bike.
This is a very loud installation! Now when I use the horn, it seems like everyone within 1/4 mile takes notice! This is the way it should be! The installation looks good also. I may relocate the compressor to an alternate location in the future, but this location kept the air hoses short, which is important for maximum volume of the horns.
Here is a view from the font. The horns are turned out just a bit. This helps to keep them away from the fender of the bike, but mostly helps to allow the sound to not be blocked by the fender or fork tubes.