Item arrived safely and is well made. If you're planning to run a pair parallel to your bookshelf speakers, you will find that the frequency cut-off is too high and the efficiency is too low. You may want a separate amplifier to up its volume. And change the condenser coil to 4.5milliHenry. My guess is the cabinet is too small to support deep bass. Speaking as an audiophile who has has 8", 10", 12" active subwoofers. My best subwoofers are a pair 3-way tower speakers with 12 woofers. Converted them into subwoofers. Changed their crossovers into low band pass circuit 125Hz. Tweeters and midrange cut off. It's the larger internal volumes that support deep bass.