Speakers least affected by room acoustics

Another for " headphones ". Also, I agree with willemj, although I believe it is with all frequencies.

If the main concern is sound reflecting off the ceiling, then either dampen it with some form of acoustic treatment, or get a loudspeaker that is specially designed to reduce vertical dispersion.   Consider something like this:

http://www.daytonaudio.com/index.php/epique-cbt24-line-array-speaker-system-pair.html

There are plenty of alternatives.  Do some research on line array loudspeakers.

Headphones are not vulnerable to acoustic waves but they are vulnerable to RF interference. The headphones per se and the cables and the electronics.

Gradient

Generally, horn, ESL and line sources. All of them control dispersion vertically. 

But still, room acoustics matter. A combination of tight dispersion control plus good room acoustic choices where you can control it is the best choice.

Reach out to GIK acoustics for attractive affordable solutions and good advice. 

Best,


Erik