Unfortunately this is not as easy as it used to be in the old days.To make an improvement ,you will need a pair of 2 tone horns.Your next problem will be finding enough space to fit them,followed by the fact that the connections will be different and the thin wiring used on modern cars inadequate.If the existing system is not relay controlled,then this will need to be fitted.If you want to take this further,then a pair of horns from a Focus would be ideal.hth

(Focus horns - gotcha. Thanks!)

I was expecting a comment like this one, and my response is that I've also considered not using the brakes to save fuel and pad wear and I never drive at night if I can avoid it, to save bulb life. Similarly I stay at home during rain, fog, snow and winds of anything over 10 mph.
HOWEVER, in real life driving conditions (and it is these in which I dwell, with 20-30,000 miles of work driving per year), the three horn functions (tap, mid tone and long toot) have their uses, do they not? I never use the horn as a greeting, rebuke or expression of impatience: if it's too late to use it before x y or z happens, then it's no use using it at all, and if another driver is brain dead, Trumpet Voluntary isn't going to re-wire his neural pathways.
I seem to remember many years ago French cars like the Citroen CX having "town and country" horns (shallow press of the button for a light tone and heavier press for a more robust warning) - a good compromise, but long since abandoned like so many good ideas in the automotive world.

This extract from a Japanese translation of driving rules for visitors, circulating in the early 1920s might explain the "tootle" sound of Japanese car horns : When a passenger of foot hove in sight tootle the horn trumpet him melodiously at first. If he still obstacles your passage tootle with vigor and express by word of mouth “Hi! Hi!”

Have you tried googling 'car horns'?

Many give their output in dB. Take your pick.

What you need is a set of these-thet don't just scare the peds out of the way-they die of fright while getting out of the way!

http://www.hornblasters.com/video.php?video=55