How big a room needed for Talon Khorus?

Does this speaker need a big room or my apptment 18x18 ?
I heard lot of good thing about Khorus.

No, they do not need a big room to sound good. But, they will certainly perform up to their potential if given some room to "breath", so to speak. Currently, I am running mine in a 11x15 (firing into long side of room) and they are absolutely stunning. 18x18 would be plenty.

Your room should be just fine. I've heard squared rooms can present some acoustic problems over rectangular rooms, but that's another point.

The Khorus is a fine speaker. I've owned a pair for about six months now. They do have a slightly more laid back presentation. A few people seem to dislike the lack of a "visceral" edge. The tradeoff--if you want to call it that--is very low distortion which brings out more detail. The bass is probably the best I've ever heard in terms of detail. It's also very deep and powerful when the source material is up to the task.

When buying you should ask when the pair was manufactured. Khorus' made after about Dec. '00 have the latest crossovers and the newer, curved speaker grills. They also have Orchard Bay cones and some other minor mods. Call Talon Audio if you have any specific questions. James Whiting--head of sales--is very helpful and happy to answer any questions. Good luck.
I currently am using the Khorus' in a 16 X 20 room facing towards the long dimension. The sound is "live" with no coloration of any kind. These speakers recreate the "live music experience" better than any others I have listened to. I have also listened to them in smaller rooms driven by mid-fi receivers with very satisfactory results. They will also sound better as they are used. Enjoy.