STLF-21500A | 21" Cast Aluminum Frame High-Power Raw Woofer Speaker, 1000 Watts Pro Audio PA DJ Replacement Subwoofer Low Frequency Driver | Reverb
Source Made in China Aluminum frame tooling speaker with 250w-500w power 6.5" car subwoofer on m.alibaba.com
Doubling the number of woofers provide further +6db of maximum output. Basically they are vertically-sta… | Open baffle speakers, Speaker box design, Speaker design