They also show a graph of short vs tall air horns:  http://www.twminduction.com/AirHorn/short_tall.html   This seems to give the impression that short is better.  The question is what their definition of short and tall is.  If short means the shorty type, then the intake just saved some space.  

Rusty,

 The short vs tall depends on the engine it's used on. On a high RPM piston  engine a short intake tract is usually best. If you have a intake that isn't "tuned" than the least restritive intake will produce more power. As a for instance on one bike I raced, a FZR 1000 Yamaha the intake tract was so short that you could almost touch an intake valve through the carb! The carbs were 43mm BTW 4X. It shows why PP engines work better at high RPM.

 If you have a short intake, (say less than 10") use whichever airhorns fit.

Bill Jepson