Review on DROK 4 Inches 4 Ohm Audio Speakers for Cars - 40W Anti-Magnetic Car Stereo Speakers with 87dB High Sensitivity, Thumping Bass, and Loudspeaker Subwoofer - Ideal for 2.0/2.1 Home Stereo, DIY Boombox, and Satellites by Rosemary Wright

This is a really cool 4" woofer! Used in a well tuned vented cabinet it's actually very low with decent output! Up to 40z with no issues, keep an eye on input power !I can't remember the exact size of the box but it was about 0.35 cu.ft with a 1.5" x 8" port. Woofer tester and BassBox is your friend! Get a pair and play around with them!Just cross them under 1k.The top end breaks quite a bit when the woofer moves a lot.