Rules for matching subwoofers to room size

Think two, rather then one large. Two ten inch, front firing should do the trick. For a discussion of 'two' check out floyd toole's 'sound reproduction' book. I have two 12 inch NHT units and have been able to verify that when only one is used, the 'coverage' is not as great as using two.

Room size is important but not first on the list.

The first thing to consider when choosing a sub is it's compatibility with your main speakers (you didn't say what they are? ;-)

You need to know/decide where/what the crossover frequency will/must be between the main and sub. It sounds like you're going to run the mains full range and just fill in with the sub (what I always recommend.) Some like to roll the mains off higher than their lowest frequency capability (to put less strain on their main amplifier) and let the sub take over below that.

The one-versus-two subs debate need not be contentious, and has a relativly simple solution: If your sub will be operating under 100Hz (under 70Hz preferred) there will be no directional information (that the human brain can identify) below that frequency anyway; and it's much easier to position a single sub for seamless matching to the main speakers. A good sized multi-driver sub like a MartinLogan Descent is my choice. Why? Plenty of output, but also great transient response with (3) 10" drivers rather than one 12" or 15" driver. The REL and the JL Audio also have great reputations.

It's also much easier to locate a single sub. Just plop it in your listening chair and then wander around your room listening for the spot(s) where the low frequencies sound best. Those are the spot(s) where you should locate the sub when YOU are in the listening chair ;-)
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