Didn't know if the DIY thread was going or not, so apologies if this is miscategorized.
Here's how I did this- Went to harbor freight and bought twin air horns and compressor for $17. They're cheap red plastic, but don't worry all this gets hidden. I made the mounting bracket from a 4" x 6"nail penetration protector plate I got at Home Depot. It was $2.70. The bracket did require some metal cutting and drilling, so if you're not able/willing to do that there's not much use to read any more. I'll be taking the bracket off to paint it black soon, so if you're interested PM me and I can probably send you a grid overlay'd pattern and you won't have to do so much figuring.
The bike had kuryakyn fake air horns behind the R saddlebag, and that's where I mounted these. They do point down, but they're really loud and put the OEM cowbell to shame. If you need the absolute best buy metal airhorns and mount them to the engine bracket pointing forward. ($200ish)
Note-it doesn't show in the pix but I drilled and cotter pinned the trumpets to the sound generating part for when the Chinese glue eventually gets overcome by vibration. Don't want that falling into my back wheel, although it would only chew it up and spit it out. Also, the compressor's only tie wrapped on, I was testing the setup out to see if I liked it before fabricating a proper bracket. I do, and I will .

 

Nice cheap mod.

 

So you have no reserve tank on the bike, correct? That means the compressor has to fire each time you engage the horn. How long does it take the compressor to build enough air pressure to effectively actuate the horn? Also, it would seem that you're gonna' get more of the horn then the person you are trying to alert.

But as was said, cheap mod. I guess.

 

Great mod, looking forward to the final report.

 

I have a Steubel air horn under my stock cover with the compressor remote mounted, no accumulator, and on cold days it takes about 1/4 second to pressurize the horn. It is a much smaller compressor than the HF one.

I doubt he is any closer to the air horns than he would be to the ugly exposed ones many people use. Cars will hear him just fine.

Nice project, I think I'll try it as well.

 

I'd say from the time I push the horn button until the sound resches my eardrum four feet away is about 172mS (milliseconds), or about one sixth of a second. Snarky, aint I??????

 

Ya' gotta' be to survive on these forums

 

OP. got any pics of what they look like WITH the saddlebag on and from the rear?

 

Sorry I didn't put those pix in, it's just that once the saddlebag's back on these horns are not visible. If you look over the bag and down between it and the frame you can just barely see them in there. I figured my bike's just a bone stock looking EG Classic, and that's about all you'd know from a side or back view.
One thing though, trust me the sound goes down, hits the ground, and bounces all around. (swear I didn't mean to make it a poem). It's an omnidirectional horn for nerds like me then. It's plenty loud too. At work they heard me honk on a road, in traffic- about a quarter mile away.
I'm going to see how many cagers I can startle into dropping their cell phones for my next endeavor.......

 

Also, sorry they're thumbs instead of embedded pictures.. I'm kind of new and I'll get better.