I just realized that the bass ring is designed to block the pressure excursion port built into the front side of the DN-2000J, like that of the AKG3003.
As mentioned by Rin Choi in his
analysis of the K3003, he blocked the port and there was about 6 dB increase in bass at 20 Hz. I foresee a similar effect with the DN-2000J's bass ring.
Personally, I prefer dynamic drivers that have adequate venting. They tend to sound more natural when they can breathe freely. So I can't imagine I'll like the effect of the bass ring, but we'll see.