Summary: I loved my F-1800RII, when it failed I bought the DD-18 and in some ways I like it better BUT as for MUSIC the DD-18 falls short of it’s predecessor. Example “my vision would get blurry from the base” I am not kidding. I do not dance but the F-1800RII made me I could not help it. Dude I had trouble seeing from the base!!!!! Not so with the DD-18, Major Bummer. My DD-18 is still MY MOST PRIZED speaker I own but it seems better for movies. Sorry Velodyne.
Summary: DD series subwoofers have a sophisticated equalization system that adjust the frequency response to the room. They come with a high quality microphone which is used during calibration to measure the output. There are many permutations of phase, polarity, gain, and crossover frequency that can make the calibration process somewhat time consuming. But the end result is tight, accurate, and powerful bass.