Originally Posted by tuxedocivic
Just to add to the data, here's a snippet of something Bossobass posted in popalock's build thread a while ago.
You can see despite room dimensions greater than 18ft there's gains from the room (ie. room gain) starting at around 35hz.
Once again as I previously stated, for the OP, the decision should be about extension, or output. I'm not pushing sealed or ported, it's your preference between those two goals.
What is "well documented" is that a room cannot support a standing wave at any frequency whose wavelength is greater than L2 (the rooms longest dimension times 2). It's a simple math formula, although actually measuring the longest dimension of most rooms is not so simple.
The idea that below L2 some weird pressure-thingy happens has not been presented in documented form on this forum to my knowledge.
Tux is correct. "Room Gain" is a phenomenon resulting from boundary gain.
Placing a point source (subs driver) within 1/8 wavelength of a corner assures only constructive reinforcement from corner reflections (left wall, right wall, floor) to the typical 80 Hz crossover point. Of course, there are many more boundaries in our rooms (opposite walls, ceiling, chases, offsets, etc.) that are further distances and which will cause reflections that are either a) destructive, b) neutral or c) constructive, as well as standing waves.
As frequency decreases, wavelength increases and the result is that more and more of the reflections become constructive and less and less of the reflections are destructive or neutral.
This is evident in every collected posted in-room FR by members over the years. All gain profiles begin in the 30-40 Hz decade, regardless of room size or whether or not the room is closed or open to the floor plan.
The amount of gain is entirely dependent on the transmission losses of the boundaries. That is, if only half of a wave is reflected back into the room and the other half is lost through the wall, the net result will be less than if the wall is concrete-filled 12" cinder block where 90% of the wave is reflected back into the room.
The ultimate extension on the low end is dominated by the cumulative signal chain roll off, which all systems have to a greater or lesser extent.
So, to answer the OP, Tux is correct. If the goal is maximum output from a given system but extension is not and system size is irrelevant, ported is the way to go. If the goal is maximum bandwidth in the smallest system size, sealed is the way to go. If multiples are in the future plans, output is irrelevant as both systems are able to exceed human tolerances of that goal.