Sealed vs Vented enclosures

The design decision to use an acoustic suspension enclosure or a ported one is completely independent of the voicing of the high frequencies. So, attributing certain high frequency characteristics to sealed enclosures or vented ones is incorrect. An acoustic suspension enclosure, properly designed, and mounted in the same volume enclosure as a ported one, will roll off more slowly below its resonance frequency, produce less harmonic distortion, or "doubling", and is less likely to have the characteristic peak or hump in frequency response near its resonance frequency. On the other hand, acoustic suspension enclosures tend to be less efficient than their vented counterparts. Vandersteen speakers certainly have bass enclosures which I believe are transmission lines. This is basically a vented design. There are excellent designs of either type and I wouldn't rule out any speaker simply based on its enclosure design.

I've never seen a sweep test of a sealed design that didn't have a hump in the upper bass (around 100 Hz). Yes, the rolloff is usually 12 dB/octave below that, but with an open baffle design, the rolloff is only 6 dB/octave. The rolloff of the bass doesn't determine quality, in and of itself.

Can we glean from your post that all acoustic suspension loudspeakers, or all at least for which you have seen a frequency sweep, start rolling off at or around 100 hz?

And would be 12 db down at 50 hz?