Are there any non air horns that are significantly louder than the stock FG horn?

Those train horns might be too big to fit, preferably a smaller unit. Anyone have any experience with the Stebels compared to the standard horn?

I used a Stebel Nautilus horn on my Vmax and it is very loud and doesn't take up much room.Available from ebay at under $50:00 .It has been on the bike for 3 years and hasn't missed a beat.It is an airhorn but quite small.Cheers Kevman.