Originally Posted by DavidA
I don't know if I would call the HE400i easier to drive than a HD-650, IMO they are both harder to drive than the average consumer HP. For me I like the low end of the HE-400i but the mids/highs of the HD-650 so depending on what type of music I want to listen to i'll pick the headphone best suited most of the time.
Technically HD-650 is easier to drive than HE-400i. it only requires 1/3 of the power required by HE-400i at the same SPL. The problem with HD-650 on portable devices like DAPs is these devices may not have enough voltage swing to drive it. High impedance load needs more voltage than what portable devices can supply.
I have a Beyer T1. It is very sensitive at 102 dB/mW compared to HE-400i @ 93 dB/mW. But HE-400i sounds very good and loud enough than my T1 directly out of Fiio X5 or iBasso DX90. The T1 simply sound underpowered on both DAPs.
On my Desktop O2+ODA, my T1 goes loud earlier than HE-400i.