[High_Q]

I've noticed this lately.  My ER4P with triple flanges and it's deep insertion, and the isolation creates the similar sound to custom IEMs.  Well at least to 1964-T as they are the only customs I've ever owned.  What do you guys think?

 

[average_joe]

Depends on the custom IEM I suppose.  I compared a HF3 (same driver as the ER4) to my Thousand Sound TS842 and though there were major differences in the bass region, which makes sense since there is a dynamic bass driver!  My experience with customs is there are more that sound different than sound similar.  I would say the Fabs and maybe SA-12 are somewhat close to the HF3.