Mini Troll" - The World's Smallest Resonance Speaker - YouTube
Amazon.com: Resonance Speaker Bluetooth Vibration Speaker 50MM 2Inch All Frequency Resonance Speaker Vibration Strong Bass Louderspeaker Compatible with Computer Laptop MP3 MP4 CD Mobile Phone PSP(4Ω 25W) : Electronics
Issues in speaker design - 2
2 Inch Resonance Speaker Vibration Strong Bass Louderspeaker All Frequency Horn Speakers 50mm 4 Ohm 25 W - AliExpress