Cos one sounds pants!!
Though for added note, try keeping your exsiting horn, as it will always sound a fraction of a second before the compressor on the air horns kick in, alternatively just fit some quality dual tone horns, I got the PIAA Monte Carlo's on mine, fitted on a homemade bracket in place of the original horn(therefore no additional relays, extra wires or heavy little compressor mounted on your inner wing)
TOOT TOOT