Originally Posted by Achmedisdead
Nobody has heard any roll-off with the 60-ohm PortaPros, to my knowledge.
Most IEMs are 32ohms at max. A lot are only 16ohms, some even less. For the Colorfly C4, measurements have shown that you need at least 50-60ohms to avoid bass roll-off. The Tera Player has not been measured so far, but in my volume-matched A/B comparisons with the 16ohms Sennheiser IE800, its bass was at least 5db down at 50Hz from my other DAPs. The only other source that sounded similar to the TP in bass was my Icon Mobile, which has substantial bass roll-off, according to GoldenEars' measurements.
There may be several explanations as to why nobody has reported any roll-off with the PortaPros. First and foremost, if the TP behaves like the C4, then any phone with more than 50-60ohms will be fine. Second, bass roll-off on a bassy phone like the PortaPro is very hard to discern wthout a volume-matched comparison. And last not least, the PortaPros' mid bass hump will mask any deep bass roll-off to a certain degree.
I'm not saying that I'm right and others are wrong, just trying to explain that observations with higher impedance phones are not necessarily contradictory to my own findings with IEMs.