Measurements inside a room are very sensitive to sub placement, listening position and the dimensions of the room. Placement against a solid wall or in a corner often gives the best low frequency reproduction. The measurements below show the response in a corner *, in down-firing position, with a 24 dB/ octave Linkwitz-Riley low pass at 60 Hz or 80 Hz without a high pass. Based on hearing alone the response drops off quickly below 17 Hz.
* One thick stone wall, one thin stone wall and a wooden floor
Cubo Infra measurements in room
Magenta: Microphone in close proximity, 24 dB/ octave low pass filter at 80 Hz Purple: Microphone in close proximity, 24 dB/ octave low pass filter at 60 Hz Turquoise: Microphone at 1 meter, 24 dB/ octave low pass filter at 60 Hz
Drivers with a very low Vas, like the SQL-12, will have low efficiency by nature, meaning they need more power to sound as loud, as for example a Lab12 driver. However, it will definitely work and even be usable down to about 14 Hz, instead of 17 Hz, it will take around 500 W to reach Xmax at that point. Then again just 250 W will already have quite insane low frequency SPL.