There must be an accepted frequency dependant maximum distance from cone to phase plug.

I think I once read 1/16th wavelength of the highest frequency of intended use. Does that ring a bell with anyone?

Anyone know of a reference?

I am looking to fit JBL drivers in my MB1's. An E120, 2204, or a 2206 would work if I used a smaller dust cap or made a spacer ring to move the driver and cover back. What I don't know is how far.