Guide to coiling whisper.

https://preview.redd.it/vy62su0w2w7f1.png?width=568&format=png&auto=webp&s=cefd7535985df8f63db91b17d09e496f5d619453

There is a lot of confusion around this ring as I have answer a lot of questiosn in other discussions, so this is my research and all the gathered information I've found out on this subreddit.

Basics:
Coiling whisper ring gives the wearer a soul every time a curse's duration hits 90% of the whole duration.
This enables a lot of builds full 45 soul stacks. 5% attack speed and 5% cast speed for each soul.

Curse duration:
This ring requires some curse duration reduction to be playable. How to achieve a playable state:
Temporal chains (lvl 1) is the lowest duration curse in the game (5 seconds). The curse effect is not applied as the ring disables curse effects, thus the real duration is 5 seconds. Also, this means that you cannot use other curses, and it doesn't matter what this curse is; only the duration matters.
Hextouch support (lvl 1, 0% qual) linked to temporal chains. 50% less duration (2.5sec now). Enables cursing on hit to linked ability (Does not work with asenath's, more about this later).
Less duration support (lvl 20, 20% qual) linked to temporal chains. 59% less duration (about 1 sec now).
(Does not work with asenaths again)

Application with hextouch:
Link one of these to your hextouch, temporal chains, less duration setup.

Herald of thunder:
https://www.reddit.com/r/pathofexile/comments/1lcfouu/coiling_whisper_soul_eater_potential_idea/
Here is a discussion about using Storm Secret and Herald of Thunder. There are two downsides to this:
Using two ring slots and a requirement to shock. Also, the OP did include an amulet, which is basically useless, as he was using frostbite instead of temporal chains. The Storm Secret Ring also damages you, but is only required for bosses, not normal mapping. Good thing about herald is, you will get stacks more reliably as you hit targets far away from you.

My favourite, Bladefall of Trarthus:
Bladefall of Trarthus automatically hits enemies in a small AOE around you. This means that you have to get close to enemies. After you get close, you need to leave the proximity to let the curse end. The curse is reapplied too fast if you stay near. If you want to stay near an enemy, you need to invest more in removing the curse faster, like warped timepiece and less duration wheel near Scion start (25% reduced and 10% less). However, on ranged builds, the gameplay is very fluid as you already run away from enemies. So, do not get hung up on this if you are not melee; you will get full stacks normally.
Problems:

1. Mana cost 5% per second. This setup is perfect for mana stackers who already have mana regeneration.
2. Requires a heavier investment for a shorter curse duration on melee characters. Need to get the curse duration lower than the bladefall of trarthus application interval.

Application with asenath's gentle touch gloves:
https://www.reddit.com/r/PathOfExileBuilds/comments/1lcowg8/permanent_capped_soul_eater_ring_gloves_without/
TLDR: Asenaths gloves automatically applies curse on hit to enemies. Also the curse stays after enemy dies. This means, that the duration can be expired even on dead enemies. However, there are problems:

1. Support gems do not affect the curse duration
2. The temporal chains is not level 1 on these gloves.
3. Could work with an additional curse setup with hextouch
4. You do not get souls during bossing
5. If you move fast enough, the bodies are culled and you do not get souls if the curse has not expired before you leave.
6. Does not work with proxies (totems, mines..) they will apply the curse but will not give you a soul.

Wilma's requital helmet:
On totem builds you can get 450% attack speed on totems with this setup.

So the perfect combination in my opinion is:
Power siphon of archmage, bladefall of trarthus setup, mana stack build with wilma's requital.
I do not have a full build for you, but you can check my current character in private league with low gear. Just barely out of campaign with no trade. https://pobb.in/8CcfTpK33nb3 This is not a full build, just an experimental character.

I also saw Jungroan doing some caster variation if you want to check him out, did not watch the stream long.

TLDR:
1. Hextouch support, Temporal chains, Less duration support, bladefall of trarthus is easy 45 soul eater stacks on ranged mana regen builds.
2. Hextouch support, Temporal chains, Less duration support, Herald of Thunder + Storm Secret is a decent alternative for shocking builds with 2-ring slot requirement. You also take damage every time herald hits.
3. Asenaths is decent choice for mapping on slow moving builds.
4. Wilma's requital allows totem builds to get 450% attack speed.

I will edit this post if there are more notes in the comments or if I forgot something.

Edit 1: Asenaths does not work with proxies (totems, mines etc..)
Edit 2: Here is a scuffed demonstration on T9 map https://www.youtube.com/watch?v=MJ2Ae0FpRXw Also I am using the wrong curse here as I was experimenting if the temporal chains effect lengthens the curse or not.