In my 40 years, the best bass comes from mass loaded transmission lines (MLTL). It's only been the past few years that a design method has been available, thanks to Martin King. Irving M. (Bud) Fried was a leading designer/advocate of MLTL's but his quirks and failed business dealings caused significant damage to his reputation. Others have latched onto the term but never applied the principles correctly, thus leading many to dismiss them. But perhaps most discount them based on lack of experience with them or the design complexities.
Much of the criticism against MLTL have been the additional expense and complication in the cabinet construction. Frankly this is way over blown and I'm sick of it. The only speaker cabinets I ever built were MLTL with the only complication being a slightly larger cabinet and two additional internal panels needed to create the labyrinth. If I can build them, it ain't so hard.
The properly designed MLTL has a 6 dB/octave roll off (to match room gain) and the vent is in phase with the driver(s). This eliminates one note bass boom and much of the issues associated with matching speakers to rooms while improving efficiency. The MLTL is open, so back pressures don't affect the driver(s) and cabinet resonances are greatly reduced. Because of the sloped internal spaces the back wave is directed away from the driver(s). This cleans up the midrange as no driver material is acoustical opaque.
I sold those MLTL cabinets because I could never afford a room big enough to do them justice. Just one session in a 20,000 cu. ft. chapel with a 20 wpc receiver proved that to me.
