Conditionally all imaginable loudspeakers in audio could be divided by two groups:

1) The loudspeakers where the pressure from the front of the loudspeaker isolated form the press from the back (Sealed enclosures, horns with sealed back chambers, infinite baffles and its…)

2) The loudspeakers where pressure from the front of the loudspeaker in any way or in any frequencies is mixed with the pressure from the back (ported enclosures and Passive Radiators, open baffles, any bandpasses, Transmission Lines, back loaded horns, TQWT and so on)

The second group of loudspeaker is FUNDAMENTALLY INFERIOR and practically at lower frequencies.  Even if the loudspeaker are made superbly and with as less as possible compromises then they still are not free from thier fundamental limitations namely - screwing the neutrality of sound reproduction and minimizing the impact of reproduced music.

Certainly you can bay whatever you want or build whatever you want but if your acoustic system allows the pressure form the back of the drivers to be injected into listening room then your loudspeakers ... are garbage and they are good enough only for pop music.

Rgs,
Romy the Cat