Ian has nicely nailed the logic behind ported designs, and you're also right, anonymous, on the efficiency question. However, a sealed-box design can produce very deep, extended bass--but you have to have lots of power to drive it. I'm using a sealed-box subwoofer in my car that produces output to 20 Hz, but it has a dedicated 180-watt RMS power amp driving only the sub. It's been said that when I play pipe-organ CDs on this system while driving at night, the headlights dim on the organ pedal notes!
Alan Lofft
Axiom Resident Expert
