I found a video to explain this It shows that particles are displaced massively more at lower frequencies, see the difference between 150hz and 20hz.
Air particles are initially moved by the membrane (or sum of membranes in DSR), if the membrane has low displacement (which APs do), then the particles have low displacement. If the membranes can't achieve the full displacement for the lower frequencies, any displacement that the membrane can provide will manifest as lower amplitude, lower volume, and will colour the sound.
I simply can't imagine a wafer thin chip to displace air like this as required by low frequencies.
jonfoulkes, regarding air porting, I'd considered that this would be an option to allow coanda / air multiplier effect, where a high velocity piston would effectively bring adjacent ambient air (collected from in front and behind) along with it so that a small piston could effect enough air to provide full displacement. I haven't seen any evidence of this in the specs, and this would ensure enclosures need to be designed to match the chips, which AP eschews. Regarding supercharging the space with high pressure air, it wouldn't work unless you also provided a super vacuum, and alternated between them at the same frequency as the sound wave and primary driver, but this is effectively just doing the job the driver should have done in the first place, and added complexity, size, weight, would be less efficient than simply making a better driver.
AKP Price at posting:
$27.30 Sentiment: None Disclosure: Not Held
(20min delay)