Restricting the vent via boundary loading creates a form of band-pass loading [think R-J style reflex loading] and while I'm sure that the wave equations can optimize the gap for 'x' amount of gain, I've never seen it published and even if I did, don?t have a clue how to manipulate it, so I have to find the amount I want empirically. Basically, it lowers tuning due to air mass loading, so can either shorten a vent or increase its area [Av] for a given Fb same as a vented TL [MLTL] does.

I worked up a simple way to find a minimum gap before it begins to audibly affect speaker response that?s based on speaker base area from empirical data and should have ?run the numbers? before posting as I get a pretty high minimum, so in theory there is some loading going on, lowering tuning [Fb], but would have to be measured or at least listen to test tones to find out how much.

Then again, this much vent area Vs cab base area makes it almost a simple TL, which by itself would be tuned to ~78.5 Hz, so ignoring floor gain, around 70 Hz may not be that far off. In retrospect, considering its age, I wonder if it?s not tuned same as an early A7, which puts it around 65 Hz, not a high tuning for the early ?50s/604D. This would imply a fairly significant amount of floor gain.

GM