Just to cut through the misunderstandings about tuned pipes in this thread.......
A tuned pipe always consists of a header + divergent cone + convergent cone + stinger. That's the tuned part!

2 or 3 chambers is a confusing term and I think it just has to do with the muffler part. Europe now only allows 3 chamber pipes because they are less noisy.
From what understand a 1 chamber pipe is just the tuned part. No muffler.
A 2 chamber pipe is the tuned part + 1 stage muffler.
A 3 chamber pipe is the tuned part + a 2 stage muffler.

[link=http://en.wikipedia.org/wiki/Expansion_chamber]Here is the link.[/link]