Elevator Music

For this achievement you will have to collect 4 Orbs of Harmony while the Elevator is going down in phase 2.

The positions of the orbs seem to be ranzomized, however a Demon Hunter can easily get all of them by Fel Rushing and Gliding: https://clips.twitch.tv/NimbleDirtyButterPraiseIt

If for some reason you failed to collect all 4 orbs on your first try, you will have to reset the instance to get orbs to spawn again.
Collecting the 4 orbs in multiple pulls does not grant you the achievement! (has been hotfixed)

This achievement becomes... "interesting" if you don't have a Demon Hunter. I've yet to see any guide to this achievement that doesn't say "just Fel Rush and glide your way to victory."
Players who can survive falls from a great height should jump off to catch the orbs. If you get lucky, the same person can grab multiple orbs if they are in a line.
We placed marks in the NW/NE/SW/NE corners of the platform, and assigned people to each mark to see where the orbs would be. Usually one corner would have multiple, with other corners having none.

The Taloc encounter is currently (as of Jan 2019) bugged, and has been for over a month. If you have to wipe, the doors at the start of the instance no longer open, and the instance must be soft-reset. Soft-resetting changes the location of all the orbs, so every attempt of this achievement involves a totally-new layout of the orbs. It's not that huge a deal, but it means that you'll just have to reassign people on the fly.

Goblin Gliders cannot be used during the encounter. You can use slow fall, but that doesn't make it easier to catch an orb since you adjust your angle afterwards. At least it's not as tricky as catching Ji'Kun's egg.