rlw6534
Headphoneus Supremus
They don't bother trying a deep seal cause of "Reasons", like using foam tips. The ER4S/SR still sounds very deep with Doom metal with heavy bass, Yeah there a quite a few bassy full range BA IEM's without any issues. The ER4B also proves these type of IEM's can have rich treble, It just amazing how flexible the ER4SR really is to EQ if you want only one headphone.
The X20i the only IEM i seen that fixes the only Single BA issue, reaching 20KHz. But the ER4S/SR comes close with high shelf of 3.5db at 10Khz.
I have and still listen to X20i regularly. They never seemed to get much love here. I do think they are a two-way BA design rather than single which may help.