What is the quietest air purifier for a single room?

I use a BIONAIRE tower, and it works great, and is really quiet. It has cut down my allergies so much, and I'm even living in a dorm, where I have little control over the cleanliness of the entire building, and people are constantly trekking in and out.

use a wet cloth & dust daily, vacuum often, mop, and keep the home clean. follow up with your allergist.