Id really love to see more of them about personally.
My sonic sonic is a corrupter though so when it comes to advising on the sonic sonic defender no can do. Id imagine aid other being useful just so that you can remove some down time from the waiting for peoples health to get back up as you dont really stop people from gettin hit, you just make them last that extra mile and make fights take that bit less in time for a meet in the middle. I have heard some people say liquefy is pretty pointless and i guess it could be. I have it on my corrupter tho and i am still despite finding some benefits judging its overall worthwhileness myself.
I also use repulsion rarely as it depends on if a person would benefit from the kb on them or not. Kins repel is awesome in the right hands and poo in the wrong ones but with repulsion ya may not know who your adding it to so sometimes it maybe just to get that person out from being in over their head, again though its overall worthwhileness is something i am sceptical about.
Out of the sonic secondaries i think shockwave to kb mobs into nearest wall (-dps) would be nice on a defender, as would screech on a ST. Howl is a multihit for -res so thats good too especially after shockwave for safety. Dreadful wail is a nice get out of a jam power imo.
My fire/fire tank loves sonics anyway, unstoppable and more damaging, need i say more?
He will honor his words; he will definitely carry out his actions. What he promises he will fulfill. He does not care about his bodily self, putting his life and death aside to come forward for another's troubled besiegement. He does not boast about his ability, or shamelessly extol his own virtues. - Sima Qian.
I can't sleep, so here's my personal rundown of the whole sonic set. I've included different sections for PvE and PvP since some powers are good for one thing and not for another.
[u]Sonic Siphon[u]
PvE: Alright-ish. Doesn't stack, so you don't really need recharges. Provides a handy -25%ish resistance debuff to the person you put it on. I don't use it that much vs normal foes since the animation is so long, but I tend to use it on AVs/GMs since you have more time to stack -res then. I'd reccomend slotting this with two accuracy and maybe one recharge to get it perma.
PvP: Pretty much like above, I don't tend to use this very often since the animation is so long. I only use it in PvP when we're stacking -res on a stone tank or something similar, otherwise I'm usually too busy finding my next cage target/buffing to use it. Two accuracy and one/two recharges is the way to go for PvP slotting.
[u]Sonic Barrier[u]
PvE: You are dumb if you do not take this. Seriously. The sonic buffs are incredibly awesome, and basically one of the main reasons to take the set. Slap 3 damres in it and you're pretty much res-capping anyone after epic shields, and providing a pretty damn good resistance boost pre-epics.
PvP: As above, except more so. Put a couple of ranges in it for PvP, and an end reduction since buffing any team over 6 people puts a big strain on your end bar.
[u]Sonic Haven[u]
PvE: As above. This shield just buffs everything other than smash/lethal/toxic.
PvP: Exactly the same.
[u]Sonic Cage[u]
PvE: Useful for putting bosses out of fights while your team mop up the rest of the mob, although it's helpful to make a bind to let them know you've done it since the FX for this power are damn near invisible. VERY situational, you could probably leave this out of your PvE build if you really wanted, but I personally wouldn't. Slot with two acc and however many recharges you particulary feel like.
PvP: Where to start? This power can literally turn the tide of any battle. It's 100% unresistable, so you can cage scrappers, tankers etc in one hit as well as everything else. Slap it on the enemies main support character and watch the rest of the team fall apart. Slot with three accuracy and three recharges and the cage becomes permanent apart from the time it takes you to fire the animation. Don't PvP without this power.
[u]Disruption Field[u]
PvE: Handy to provide that extra bit of damage, since this provides a -15% resistance AoE field around whichever teammate you put this on. Be careful, though, since this will get you aggro if whatever you drop this on does not have a damage/taunt aura. I usually like to put this on tankers who are definitely running their taunt auras, or scrappers running powers like quills or death shroud. Put two endrdx in this power, since it can be quite end heavy when coupled with your other toggles.
PvP: I had trouble using this power in PvP because it only has a really short range. I found that even superjumping as high as I could would put me out of range of the person I had it on, so I dropped it from my build. It could be handy, though, in situations like base raids where everyone is likely to be less mobile and more close together. Two endrdx as above.
[u]Sonic Dispertion[u]
PvE: As with the single target buffs, you are dumb if you do not take this power. It provides a decent resistance boost to you and those around you, as well as protection from disorients, holds and immobilizes. Slot it with 3 damres and 3 endrdx.
PvP: As above pretty much.
[u]Sonic Repulsion[u]
PvE: Don't bother. All this power does is miss all the time until it uses all your endurance (which happens really fast) since it has an accuracy check and yet is unslottable for accuracy. I have never found a use for this, ever.
PvP: Waste of a power. Plain and simple. No, it doesn't work as stalker defence.
[u]Clarity[u]
PvE: Clear Mind with a different name. I would never expect an Empath to be without Clear Mind, so a sonic is no different. Slot it with one range.
PvP: Pretty much as above, except that it's better than CM because its animation is much much shorter. Slot with three recharges and three ranges for maximum stacking.
[u]Liquefy:[u]
PvE: No. Just no. It's basically a subpar version of ice slick, except it has a longer recharge. The hold element of it lasts like two seconds, and the tohitdebuff and defence debuff aren't even noticable.
PvP: Ahahahaha. Never take this power for PvP. People will just run out of the debuff, or they won't stand still for long enough for you to actually hit them with it in the first place.
And now onto the blasts. Sonic Blast is the ONLY blast set worth taking on a sonic defender, really, since the two sets synergize so well.
[u]Shriek[u]
PvE: Single target low-ish damage attack. You have to take this, but it's not that bad. If you're going to try and do damage, though, I wouldn't bother slotting this. I have it to stack -resistance on AVs, though, since it stacks with itself and so I've put two accuracy and three recharges in it.
PvP: Pretty much the same as sonic siphon except it has a smaller animation and stacks with itself. Two acc, three recharge.
[u]Scream[u]
PvE: A whole lotta dots. Pretty good damage, plus it lets you ninja kills from other people because it's DoT :P I have it for stacking -resistance with Shriek, so I have two accuracy and three recharges in it. If you're going for damage, put three damage in there instead of recharge and stick an endrdx on the end.
PvP: As above pretty much. With three recharges in both shriek and scream they cycle almost instantly and you can stack something stupid like -120% resistance on a single target - enough to reduce even a granite tank to his knees.
[u]Howl[u]
PvE: Average-ish damage cone. A nice attack if you get hit with fulcrum or something. Two acc, three recharge, one endrdx.
PvP: Single target is pretty much king in PvP, so I wouldn't bother with this power. Besides, sonics are generally meant for team builds so your blaster/scrappers should be doing the main bulk of the damage on your debuffed targets.
[u]Shockwave[u]
PvE: Gale with a different name, right down to having the same animation. It has a little more damage than gale, but apart from that it's about as useful. Take it if you like knockback. Personally I don't like KB enough to take this power.
PvP: As with Howl, it's not that great. Most sensible PvPers are running Acrobatics anyway, so this power is practically useless.
[u]Shout[u]
PvE: Short range, high damage attack like the description says. This attack actually does a fair bit of damage, but has a pretty long recharge so isn't that great for stacking -resistance. Two acc/three damage/one endrdx as standard.
PvP: Pretty much as above.
[u]Amplify[u]
PvE: Aim with a different name. Useful but not neccesary for PvE. Slot it with three recharges and as many tohit buffs as you can spare.
PvP: Basically required. Use this before your cage to damn-near guarantee a hit unless they've popped a whole ton of purples. Slot with three recharges and three tohit buffs.
[u]Sirens Song[u]
PvE: Cone Sleep with a pretty decent duration. If your team are careful, you can make any mob a walkover with this power. Slot it with two accuracy as standard, and then if you feel like it you could put a few recharges/sleep durations in it although the base recharge/duration is pretty good already.
PvP: Another cone, except this one has a stupidly long animation (the same as Decieve from illusion). It is a sleep, but it takes so long to fire that the blaster on your team could have probably killed the person you're trying to sleep before the animation is finished. I had this for a while, but found it pretty useless. Don't bother.
[u]Screech[u]
PvE: As useful as you'd expect any low-damage single target stun to be, really. As with Sirens Song, slap two accuracy in it and then recharges/durations to taste.
PvP: Bloody annoying. This is useful for knocking acrobatics off'f squishies so your team can bounce them around, and the range is nice too. Two acc, durations/recharges to taste.
[u]Dreadful Wail[u]
PvE: It's a nuke, but it's a defender nuke so the damage pretty much stinks. I used to use this after being hit with fulcrum shift, and I guess it was pretty good then. On its own, though, the damage is awful even though it makes a cool noise. It is an AoE -resistance and a stun though so that makes it a little more useful than other defender nukes. Having said that, it leaves you with 0 end. If you really have to have it, slot it with 1 acc 3 damage and 2 recharge and only use it after firing amplify.
PvP: Only really useful in a baseraid after you've had a load of +damage buffs dropped on you and you don't have anything else to do. So never, basically. If you do want to use it, slot it like you would for PvE. I wouldn't, though. Ever.
[u]Epic Powers[u]
Basically the psi epic is the only way to go for sonic/sonic defenders since power doesn't add anything new as your buffs aren't able to be powerboosted. TK is useful in both PvE and PvP, and the epic shield will take you to damn near the res cap when stacked with Sonic Dispertion. Dominate is a handy single target mez, although I don't use it that much in PvP, and Mass Hypnosis is useful to fling if you miss a few enemies with Sirens Song in PvE.
[u]Pool Powers[u]
Personally on my sonic I have Fitness (Swift, Hurdle, Stamina), Leaping (CJ, SJ, Acrobatics), Speed (Hasten, SS) and Concealment (Stealth, Grant Invis, Phase Shift). I'm all PvP built though, so you could probably take out Phase shift. Acrobatics is handy just for filling in the holes in Sonic Dispertion (although you're still vulnerable to sleeps). Hasten makes fun powers like Amplify come back up more often, although it will mess up your cage cycle in PvP (although if you use amplify at the same time this recharges as the cage drops on your target). Grant Invis is handy for putting on the squishies in your team to stop them from getting any extra aggro in PvE, and it drops debuff toggles on your team in PvP. Fitness is a must, seriously, since sonic is so end heavy. Don't bother with aid other, it takes up too much time where you could be doing something more useful. I never really found any of the other pools that hot either, since you don't have the endurance to run leadership toggles, or in fact any more toggles at all.
Holy cow. I might just repost this in guides, since I wrote so much :P
P.S. I just read through my post before posting and I forgot to say that sonic is awesome, so I'll do it now. Sonic is awesome.
VERY nice work Xanthus, should definately put that into the Guide section.
I only disagree with you on one small point- you don't *need* to take the sonic secondary! 
I rolled a very odd combo for my Sonic Defender, Sonic/Elec. It's a pure support toon and used a fairly different build when levelling than it currently has at level 50, because damage output of /elec is very low which made the occasional soloing session quite tricky.
At first glance the powersets might seem at odds with each other, but they actually have some synergy: Sonic gets a very good single-target damage mitigation power in Sonic Cage, and Elec gets a very good AoE damage mitigation power in Short Circuit (and a ranged hold).
Combined with the Elec Epic Pool's 'Power Sink' or 'Power Build Up' from the Power Mastery pool you can completely cripple most normal PvE mobs. With just three attacks you can drain all the endurance of the mob and cage a Boss/AV at the same time. You also get self/team mez protection and very good damage resistance, so you can quite happily survive in the middle of the mob in order to use your endurance drains.
Your Smashing/Lethal resistance is very nearly capped just from Sonic Dispersion and your epic shield, and if you take the Elec Epic Pool you get a very nice level of energy resistance too.
My only gripe with the build is that it's very, very low on damage output when soloing.
It brings a LOT to a team though: -60% res, Sonic Cage, Short Circuit/Power Sink, 55% team damage resistance to all but Psi, a stackable targetted +perception/mez protection buff, PBAoE team mez protection that's nearly on-par with Integration, Tesla Cage for sappers... I also took Aid other/Aid Self on it so it's usually able to keep even large teams alive when it's the only support toon available.
It's certainly not as good as /Sonic for stacking resistances and it doesn't get a ranged disorient, it's more a team-defence toon than a team-attack toon. You also need to be very aware that you have a gap in your self-mez protection: Sleep attacks will detoggle you. It's mainly Freakshow and Carnies that use ranged attacks with "sleep" components, so be extra-careful when fighting them.
Am I the only one that thinks Sonic Blast should inherently have KB? I mean you're hit in the chest by a blast of sound, surely there'd be some kinda knockback?
The defence set feels alot like a retconned FF set imo. I'll give it a shot tho, see if I like the feel. If not, it'll be a Sonic Blaster 
Thanks a lot Xanthus Really helped
I'd love KB on sonic blasts, but I guess then all the energy blasters would get annoyed.
If you don't like it, do try the sonic blaster, lots of fun. 
@Dante EU - Union Roleplayer and Altisis Victim
The Militia: Union RP Supergroup - www.themilitia.org.uk
TBH I think knockback in all the attacks would be counterproductive with Sonic's ally-anchored -res debuff, you'd keep knocking them out of the debuff aura.
And you'd annoy melee toons nearly as much as NRG blasters...
Actually, if they gave Sonic Blast attacks knockback they'd probably take the -res away. Dooooooooom!! 
Yeah s'pose. I'll give them a shot Kinda wanted a debuff animation where the mobs either clutched their heads in agony or threw up due to sound induced nausea thus rendering them held
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I'd love KB on sonic blasts, but I guess then all the energy blasters would get annoyed.
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Im annoyed by my own KB attacks mostly..
I guess I´ll have to shoot the next one to suggest adding KB to sonic attacks.
I would hate having to delete one of my favourite toons at level 50 which I definitely would if they added KB.
Kinetic + Knockback = Self-Nerf
If it has eyes, you can blind it, if it has blood, you can make it bleed, if it has a mouth, you can make it scream.
If you read Xanthus's essay on city of heroes this may not apply to you.
I find sonics good - especially to invul scrappers/tanks makes them last a lot longer. Helps with taking down AV's n stuff like that also.
I've been toying with a concept for a Sonic/Sonic Defender and wanted to hear people's opinions on them?