[KosanRio]

I just bought a pair of RHA MA750i's to use primarily with my iPhone 6s Plus. I didn't realize that it actually has something like a 4-5ohm impedance output, all my previous Android phones have been like 1-2Ohm. I know there is that 1/8th rule, for example in theory I should be using at the minimum 32Ohm headphones with a 4Ohm output impedance source. By using 16Ohm headphones on a 4Ohm source am I going to get bass roll off? or any other weird things like that? Thanks.

 

[KosanRio]

Any ideas guys?

 

[Music Alchemist]

Should be fine.

http://www.kenrockwell.com/apple/iphone-6s-plus-audio-quality.htm

The most extreme example I encountered was when I was using an amp with 80 ohms output impedance, which gave it crazy bass. You're not likely to have issues with the iPhone.

 

[Intensecure]

The impedance issue mainly occurs with BA drivers, which can be sensitive to output. Dynamic drivers are not nearly so dependant on source. And the issue usually happens with dramatic mismatches, which isn't your case.
Simply put, you have nothing to worry about and I doubt that there would be any difference in switching to a lower impedance output.
Enjoy!