Indeed Hamwich ... as a lapsed Bass player, lugging 18" cabs about in the '60s meant I never needed a gym!
I'm also bemused by the 90% claim ..... modern car speakers are pretty light and compact .... even using the internal panels as the actual sound-board means you still need the driver ... and that's the heavy bit, the diaphragm weighs nothing .... unless they're looking at an 18" vibrating panel and saying it's 90% lighter than an 18" bass speaker would be? 🙂
K