What Are the Physics Behind Exponential Horns and Air Expansion?

[HengHY]

I am trying to understand the physics of an exponential horn. I got most of my references online and according to the Horn Physics by Martin King, the volume velocity at the mouth is greater than the applied volume velocity at the throat (the horn is driven by a speaker/buzzer).
This is what i think
Volume velocity = velocity*cross sectional area
If this is true then the air expands when it passes through the horn (the air density decreases). Can this be true even though the velocity is subsonic?
Any possible cheap method to justify that? I have limited books to read.

Cheers

 

[tiny-tim]

Hi HengHY!

A good resource for musical instrument science is the australian site http://www.phys.unsw.edu.au/jw/brassacoustics.html"