[brucepick]

Like an earlier post here, I used junkyard horns.

Car originally had 2 in front of radiator. I removed them, put two behind each corner of front bumper. Sound comes out wheel wells due to lots of clearance there. Powered by relays. I got the horns from junker Volvos but I think most stock horns from medium-large cars should be pretty loud. Two horns of different pitches are more piercing than two of same pitch.

I find most offending cars that need to hear my horns are approaching from the side, not from ahead of me. So the side horns do a great job. You can hear them in front too of course.