Image 1/3: At long last we've found the [http://www.sonos.com/shop/products/play3|advertised] [http://en.wikipedia.org/wiki/Passive_radiator_(speaker)|bass radiator], a passive speaker cone secured in the very back of the case that forms an inexpensive alternative to a powered subwoofer.
DIY Portable Bluetooth Speaker 30W, BT4.0, Passive Radiators
DIY Portable Bluetooth Speaker 30W, BT4.0, Passive Radiators - All
Dayton Audio SD175-PR 6-1/2" Passive Radiator
Edifier Exclaim Bi-Amped 2.0 Speaker System (e10) Each upper section of the speaker contains two 11/2 inch midrange/ tweeters, and a 11/2 inch x 3 inch passive radiator Edifier
Speaker Parts and Components: Ess Tempest And Model 8 Speaker Repair Kit - 8 Woofer And 10 Passive Radiators -> BUY IT NOW ONLY: $49.45 on eBay!