I have both Sonic Cage and Sonic Disruption on one of my 'trollers, and wouldn't be without them.
@Synaesthetix
"Here, take some more bees with you. You may need them."
Union: FU//LoUD
"that Syn is that that" - Mothers Love
The only problem with sonic cage type powers is that they won't be affected by aoe attacks which go a long way in the war of attrition which is killing the baddies in the post-ED world.
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3- Sonic Repulsion:
Description: You create a powerful sonic resonance around an ally, repelling all foes nearby. You will lose endurance for each target repelled.
This power might depend on your interest for Raids and PvP. Giving Sonic Repulsion to a MM/Controller/Dominator will avoid the AS's of Stalkers on Raid missions and PvP. */EA Stalkers might be able of AS across repel shields, but if you give'em Clarity they will have +perception, so they can just avoid the stalkers easily.
[/ QUOTE ]One problem: It's knockback, not repel, so nearly any melee player can get through it (apart for, of the top of my head, /DA /FA and /ninja, unless they run acrobatics).
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2- Disruption Field:
Description: You set up a constant wave of sonic energy around an ally, weakening the Damage Resistance of all nearby foes.
For me this one seems pretty obvious. Just give it to a brute.. Usually brutes go straight to the Boss/Av/Eb/hugemobs and smash them while building fury. With the Disruption Field, brutes will weaken all foes around'em, making the target much easier to be killed.
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it seems pretty usefull yes, but unless the brute has an AoE taunt or something, or can get immediate attention, because, yes, the aggro the disruption field gets, is directed onto you (at least it was in i5, not sure if they fixed it, i respecced it out because of that), and constantly retoggeling while the brute has just jumped in is a hassle 
If they fix(ed) the aggro problem, it is indeed a nice power to have (bit hefty end cost tho iirc)
this was on my lvl 30 son/psy defender btw
@Shift
Shift 50 DM/DA Scrapper ][ TTL 50 Kat/Reg Scrapper ][ Shabriel 50 Peacebringer ][ Ion Shift 46 Rad/Rad Corruptor ][ Thermal Shift 35 Fire/Fire Blaster
"A Scrapper is a lot like a chainsaw. Somewhat hard to handle, incredibly dangerous, and by far the most fun when wielded by the slightly insane."
I've been reading several topics about sonic builds (uk and us boards) and it seems most people don't like /sonic powers just like sonic cage, disruption field and sonic repulsion. I admit I'm not an expert but for me they seem to be extremly useful. Imagine the following situations:
1- Sonic Cage:
Description: Encases the target in an impenetrable field of sonic waves. The target cannot attack or be attacked.
I'll go straight to the point. You are in a CoT mission and you have to defeat Boss and guards. While u make ur way to the boss you'll certainly find the unloved Succubus surrounded by earth mages, spectrals etc etc.. Sonic Cage can be extremly useful here. Usually the team decides to pick on Succubus first because of its annoying power and placates. With Sonic Cage you can just take her off of combat while u take off the stewpid minions and lieus. Then you wont have a problem bashing her when shes all alone. Another situation is when you have more than one boss in the same room. You Sonic Cage one while the team bashes the other.
2- Disruption Field:
Description: You set up a constant wave of sonic energy around an ally, weakening the Damage Resistance of all nearby foes.
For me this one seems pretty obvious. Just give it to a brute.. Usually brutes go straight to the Boss/Av/Eb/hugemobs and smash them while building fury. With the Disruption Field, brutes will weaken all foes around'em, making the target much easier to be killed.
3- Sonic Repulsion:
Description: You create a powerful sonic resonance around an ally, repelling all foes nearby. You will lose endurance for each target repelled.
This power might depend on your interest for Raids and PvP. Giving Sonic Repulsion to a MM/Controller/Dominator will avoid the AS's of Stalkers on Raid missions and PvP. */EA Stalkers might be able of AS across repel shields, but if you give'em Clarity they will have +perception, so they can just avoid the stalkers easily.
Once again, I'm just a rookie on Sonic builds and this is my opinion only. Maybe those 3 powers should be picked only at higher lvls, after you get stamina, but they ARE useful.
Feel free to comment ;]
@False Fiction - Virtue / Defiant
Current projects - [Glaciologist - Ill/Cold Troller] [Cloudshaper - Storm/Dark Def] [Harald Wartooth - Elec/Psi Domi]