@erik_squires wrote: "That’s an interesting POV. I would have thought that the slot [the area between back of a speaker with a rear-firing tweeter and the well immediately behind it] would act like a severe low pass filter."
Sorry I over looked responding to this earlier.
I manufacture a bass guitar speaker cabinet which uses a 3" cone unit for the top end. It’s gently highpassed around 1.5 kHz or so. Behind the cone is a wide, shallow isolation chamber which extends laterally the full width of the cabinet, with generous openings on the top and sides. So, it’s a slot of sorts. The openings allow enough of the 3" cone’s backwave energy to escape out the top and sides that the bass player can clearly hear his overtones even if he is virtually atop the cab, and I’ve gotten feedback that the other musicians can better hear what the bass player is doing as well.
I’m sure there are some losses in the slot behind the 3" cone, but it’s still making a worthwhile contribution, so I don’t think the net effect is a particularly severe lowpass filter.
Duke