[VR Baron]

Originally Posted by Sleez

shape doesn't matter, length is where it's at, ahem!!!

it's also a good idea to make an end cap that gives you a bit of adjustment, +- an inch or two. the diameter effects the volume of air mass, and effects the usefulness a bit.

"When air is forced into a cavity, the pressure inside increases. When the external force pushing the air into the cavity is removed, the higher-pressure air inside will flow out. The cavity will be left at a pressure slightly lower than the outside, causing air to be drawn back in. This process repeats with the magnitude of the pressure changes decreasing each time.
The air in the port (the neck of the chamber) has mass. Since it is in motion, it possesses some momentum. A longer port would make for a larger mass, and vice-versa. The diameter of the port is related to the mass of air and the volume of the chamber. A port that is too small in area for the chamber volume will "choke" the flow while one that is too large in area for the chamber volume tends to reduce the momentum of the air in the port."

see more here; http://en.wikipedia.org/wiki/Helmholtz_resonance

There you go!