I would guess because the DT had a passive radiator, basically acting like it’s ported. The REL is sealed as I think all their subs are.
BMRs are similar but not identical to ported alignments. Ported enclosures roll of 24 db. per octave below F3, but ABRs roll off at 36 db. That is a major significant difference. One result of this is to encourage extended bass alignments, which are not as tight.
In general commercial designs go for extended alignments which encourages the ad men, and probably does boost sales, but in my view that is the wrong bargain.
The extended alignments are more resonant and have worse transient response. So, I stay away from extended bass alignments in my designs and they are the better for it.
The other myth is that sealed enclosures have a tighter response, as they require a higher Qts driver. And a sealed box with a spring (the driver) is still a resonant system. Not only that, sealed boxes have a nasty habit of having a peak before roll off, which can give them an unnatural false bass.
The only way I know of to get a truly non resonant bass is with an open baffle arrangement, which brings a whole host of problems. The other, which is what I favor, and that is an aperiodically damped transmission line. Those are the only alignments I know that will give a truly realistic powerful uncolored bass. Once you have experienced that, there is no other way to go. Horns are also in the running, but require low Qts drivers, and unless driver and enclosure is massive they will not deliver true sub range, as we have come to know it. But they certainly have commercial applications for large venues.
