I was idly looking at various speaker design, just in the off chance that I might get the bug and build a set. I seem to remember seeing, some years ago (dimly, through some sort of haze or fog), a speaker cabinet design that used a tall box, with a vertical slot of varying width. The driver was at the bottom, facing upward. The slot started low and narrow, and was nearly as wide as the whole enclosure near the top. It looked to be an exponential curve. I can't remember anything else about this, whether it was just an oddity or had some particular interesting feature. Anyone have any idea?