haha... its all about the box design, and the SPECIFIC subs you are using. Put an MTX RFL 15 in a box and throw 30hz to it, and tell me it plays better lower (if at all without roasting) than an Orion H2 10... you will eat words quickly.

My single 12 box was an amazingly low hitting box peaking at 40hz, yet my current 15 box is tuned high and peaks @ 64hz . Anyways, enough of my rambling.

Get a good set of subs, and a good amp to power them, and compliment those items with a quality box tuned correctly for what you desire, and voila, you are happy.