Danley Sound Labs' Matterhorn Subwoofer may be the world's biggest--at least I hope it is. The mother of all subs has 40,000 watts of power, and the whole thing is built into a 20x8x8 foot shipping container. I guess that makes it easy to return when you blow it up! It looks like too much of a good thing to me.
More is just more; it's not necessarily better. True, the more drivers a sub has the lower the distortion, but I think the Matterhorn may have passed the point of diminishing returns. Just kidding, the Matterhorn isn't a consumer product, but large audiophile subs tend to sound better than most 1-foot cube models. Mini subs can pack a wallop, it's just that they tend to sound boomy and muddled. They're not great for music.
I reviewed the original Outlaw Audio LFM-1 subwoofer here at CNET a few years ago and was mightily impressed with its deep bass power and rock-solid definition. It was equally phenomenal on home theater and music.
The current model, the LFM-1 Plus, is a large beast all right; it's 21.75x15x22 inches, and features a 12-inch woofer and a 350-watt amplifier. It's just $499. So yes, size does matter, and if you really want to rock your world buy two. Multiple subwoofers are a good idea for a number of reasons I'll cover in a future blog. Outlaw sells pairs of LFM-1 Plus subs for $899. Check their site for more info.