The Tuned Length

Hi All,
We all know what we mean by the tuned length for an expansion chamber and probably have different formulae for same, I for one used the Graham Bell paper for many years " albeit out of date" but it gave me a good starting point to work from.
Now the question I ask is, can anyone out there in Bantam land tell me the exact point at which the positive wave will reach in the baffle cone before returning back up the pipe in order to plug the exhaust. Mr Bell says it is half way of the total length of the cone before cutting the tail pipe diameter, the paper from Lukes Racing Engines 20/10/2014 says " The sound wave traveling down the pipe bounces off the baffle cone and returns to the exhaust port ect" but at what point is what I want to know.
I think JB's idea for an adjustable centre section a good one, could save a lot of cutting and suck it and see.
Anyway I'm ready to learn if you have the answer.

Happy new year and success in your quest for victory.

Les2012.

Les,
Go to page 10 on the forum, click on "Pipe Design" the formula for t/l and a lot more is there for you to look at!
Leave Bell in his era, technology has moved on since then.

Trevor