> Unfortunately, if it is possible, nobody seems to have figured out how to do it.
I'm not sure if you're referring to directional bass or to small speakers making decent bass. The former is fortunately a solved problem today - cardiod speakers (and their variants) do so, albeit DSP may be required/help.
For the latter, the issue is partly because you need to move double the air volume for every halvening of an ocatve. So going from 120hz to 30hz requires 4 times more moved air for same dBspl... but because of human ear (insensitivity), we need way more loudness at lower frequencies to sound "as loud" (Fletcher Munson curve or dbA weighting). Consequently it's kinda hard to get loud enough bass from small drivers (I can explain in more detail if you'd like). There's some interesting tech like Mayht speakers and Resonado but in its current form there are limitations.
It's still kind of the same issue. At the end of the day you need to move a lot of air for the bass. In theory some kind of air multiplier might allow these small-excursion ultrasonic speakers to do that, but unless there's a very good reason (or DARPA $$$) it's just more practical to do it conventionally.
I'm not sure if you're referring to directional bass or to small speakers making decent bass. The former is fortunately a solved problem today - cardiod speakers (and their variants) do so, albeit DSP may be required/help.
For the latter, the issue is partly because you need to move double the air volume for every halvening of an ocatve. So going from 120hz to 30hz requires 4 times more moved air for same dBspl... but because of human ear (insensitivity), we need way more loudness at lower frequencies to sound "as loud" (Fletcher Munson curve or dbA weighting). Consequently it's kinda hard to get loud enough bass from small drivers (I can explain in more detail if you'd like). There's some interesting tech like Mayht speakers and Resonado but in its current form there are limitations.