A while ago I wrote that I installed twin air horns into the bike. 
Yep, even louder than the exhaust... especially now that the can is repacked.

This is a major safety mod that I would recommend to everybody
as the stock horn will not alert cars to your presence.
It's a piece of shit and you can't rely on it to save you in an emergency.
(Mr Suzuki should have his gonads removed for that one.)

In an emergency you need every bit of assistance you can get.
It's obvious without explanation that more powerful horns might save you...

Well, once again there are no hard and fast rules for this mod, but there is not much room 
and so your decisions in purchasing a horn set should be governed by that.

Hunt for room! The indicator mod that I did freed up some room in the fairing. 

Then I mixed and matched horns from both a 2 & a 3 horn system.
I bought a 3 horn set & used the two smaller ones only in the across. 
I bought a two horn set for one of the cars & installed the 3 larger horns on that.

Air horns always come with a relay. Make sure you use it. The standard
electrical cables will not handle the current draw from an air horn compressor.

There will be instructions provided with the horns for wiring the relay.

Nothing too complex here. You are setting up a new circuit for power which 
runs straight from the battery to the compressor. You are turning that circuit on and off with
the old circuit that used to run power to the horns via the horn button on the handlebar.
That way the old circuit is not being loaded with the heavy current that the compressor demands.
You could probably leave the old horn in line as a fail safe, though I took mine off.

Use a heavy guage cable for the compressor circuit, as you can see in some of the shots below.
The high current circuit should also have it's own fuse, at whatever rating that the horn mfr. recommends.
Mine's a yellow fuse, whatever rating that is... about 20 amp?

I put the compressor here. It is one of the large types. 

Front lower fairing, looking towards left leg side. 

You can get a set of air horns with a smaller compressor than mine, 
which is obviously better. Go for it if you can find it.

Someone on the EzBoard set up airhorns and cable tied the compressor to the space above the engine,
on the radiator fluid reservoir side of the bike. I checked it out and you can get a compressor in there;
I just don't know about heat issues Vs. the tubing that runs to the horns, or the electrical cable feeding the compressor.
Or, for that matter, how susceptible the compressor is to the heat.
In the face of ignorance, I go for the option that I assume is safer... 
at least more likely to keep those horns working for when you need them.
They also used a single air horn... it is easy to do this with the air horn kits 
and it still makes for a very loud horn, no doubt.

Try to run some metal plate from other places to reinforce the mounting 
point of the compressor if you mount it here,
as the compressor is quite a heavy little thing.

Horns.

Here's a view over the top of the front of the fairing into the space where 
you can see the tip of the compressor and one of the two horns being fed.

An essential point to note is not to hang your petrol powered garden mulcher 
above your bike or it may leak crap onto your fairing, as seen around that 
philips head screw. OK, it's not essential to note that. Just making excuses.

Here's a shot a little further back to show the dog's breakfast that is going on here.
I chose to mount the relay just off the left mounting point for the fuel lights,
so it's hanging out a bit. 
(Yes it could have been much tidier... I will fix it and post another shot
later. The rush to get the horn in took precedence over the looks of the job.
Safety was more important.)

This shot shows you where I put the second horn, 
facing downwards, out towards the front wheel.
This horn is 's also mounted off of that fuel light point, with the relay.

Really Important.
You have to make sure that everything clears the front forks through their whole 
travel, which ends up being the trickiest bit for space.

So how loud is it? If I don't have my helmet visor down when I hit the horn,
it causes reasonable pain to my ears. That's loud.
And a world away from that pathetic excuse for a horn 
that is supplied stock.

This is just one solution that I found to get the horns in... 
make your one even better and send me piccies for this page!