[SyneRyder]

Any reason why you recommend against active noise cancellation? My Bose QC25s are still my favorite purchase, combining both over-ear passive cancellation & active noise cancellation. I even use them when working solo, and was so freaked out when one pair broke that I bought a second backup pair - Bose replaced the broken pair free of charge though.

[I realize the OP mentioned that headphones were not an option though.]

[kbar13]

active noise cancellation is extremely effective for ambient noise but not conversations, which are the main cause of distraction in an open plan office.

[jkot]

I personally find active headphones uncomfortable. Large studio headphones are designed for long term use.

[loco5niner]

The reference was not to 'active headphones' (e.g. for running), but to 'active noise cancellation' where an "inverse wave" (inverse to incoming noise) is played to cancel out sounds. These can be in both in-ear or over-the-ear form.