Closed or Open IEMs. What's the impact?

[OK1]

Wishing to understand better. In the speaker world, there are well reviewed professional speakers using either closed or open (i,e ported) designs. Same for Hi-Fi. In the live audio world, almost everything is ported (cant think of a non ported live audio speaker I have ever come across).

With headphones, the informed opinion is - open or semi open, is best, for critical listening, e,g Sennheiser HD650 (open) or AKG K702 (semi open), ostensibly to reduce the reflections from the housing of the headphones, muddying up the sound.

So with IEM's is this choice of any significance? Open, semi open, closed. and why?

 

[Dunring]

I prefer closed design for critical listening because the better noise isolation helps. Noise floor is the other important thing for picking out details. Getting the chain you plug into as quiet as possible lets details jump out more.
With some like the KZ PR2 it's got vents on the side, but the sound leakage even when the air conditioner blows was distracting.

 

[markanini]

You can open the shell of most IEMs without a change is frequency response because the sealing of the back volume is usually part of the driver assembly. A true open back IEM would probably graph something like an earbud. Some IEM marketing talks about open-back design but this is something of a red herring acoustically.