Amazon.com: CQRobot Speaker 3 Watt 4 Ohm Compatible with Arduino Motherboard, 2.54mm Dupont Interface. It is Ideal for a Variety of Small Electronic Projects. : Electronics
Amazon.com: CHOOYO 6.5 Inch Subwoofer Speakers 80W 4 8 Ohm High Power HiFi Fever Woofer Music Audio Bookshelf Loudspeaker DIY Sound System (Color : 4 Ohm) : Electronics
Amazon.com: PyleUsa Car Midbass Speaker System - Pro 8" 600W 4 Ohm Mid-Bass Component Woofer Audio Sound Speakers for Car Stereo w/ 40oz Magnet,Tweeters, Grills, 45Hz-4KHz Frequency, 3.1” Mount Depth-PLG8C (Pair) :
Amazon.com: 12V Low Pass Speaker Subwoofer Crossover for 8 Ohm or 4 Ohm : Electronics
Amazon.com: Facmogu 2PCS 8 Inch Full Range Audio Speakers, RMS 50W Peak 120W 4 Ohm, Car Vehicle Audio Full Range Drivers, Wide Range Bass Woofer DIY Loudspeaker Replacement - Yellow : Electronics