Here is my impression after 3 weeks of using the Radius NHR21. Earphone has been burned for about 8 hours. At that moment I used Sony Walkman NWA-30.
"Bass-head" is all I can say. It is the heaviest, articulating, and textured bass I have ever heard in my collection. It exceeds my bass-heavy collection like JVC FX101, Sony XBA-A3, EPH-100, Carbo Basso, and JVC FX750.
It rattles ear-drum on heavy-bass tracks and this is the only earphone in my collection that gives audible bass-rumbles. However it can get nauseating as well, especially for me who's not a bass-head listener. Even the bass dominates on light track. It was fatiguing and too powerful to handle. On top of that the mid was too recessed and sparkle was nearly non-existent - this reminds me of disappointing Yamaha EPH-M200 which I reviewed back and returned.
Details were muddied by the bass and clarity is disappointing given that its priced at $100 USD and labeled as "High-Res". Radius NHR21 is a prime example of what a bad-tuned JVC FXZ200 would be, as the FXZ200 is a good warm and balanced earphone with pleasant amount of bass.
Furthermore the earphone is very sensitive and the bass still audible even at small volume. Most people think sensitive earphones tend to get too bright and and thin sounding but this one gives big fat bass at low-volume. l I can't imagine living with the NHR31 which is more sensitive than the NHR21 and 2-3 times more expensive as well.
I was at the verge of selling the earphone but I changed my mind when I switched its stock tips with Spin-fit eartips and paired with iBasso DX80. This combination fixes the nauseating bass and muddy clarity. Now the bass smoothen out, bass punch was lighter, midrange and treble lifted up, and sparkles are more existent. In other word, they are all balanced out.
Still I hardly can recommend Radius NHR21. I'd rate 6.5 out of 10 for the sound quality vs price. Earphone was rather big to my ear and slightly protrudes but it is not as big as the gargantuan-sized ATH-CKS1100. If one has bass-heavy earphone like EPH-100, Sony XBA-A3, JVC HA-FX101, or the FXH30 and the FX750, and look for a heavier one, do not even bother with the NHR21. Instead if one look for a good bass-heavy earphone in $100 USD I'd recommend on 1More triple hybrid earphone, which is far more balanced than it.
The NHR21 bass is just too excessive to my ear, could it be it was paired with a mismatching player.