I can't help you with the weight of a Tuba, but depending on materials (type of plywood, epoxies, etc.) a Lab typically weighs in between 240 and 275. A regards the drivers, I've been running Labs since the first batch of drivers became available. I have had two failures and both were determined by Eminence to be manufacturing faults ( the first was a shorted coil, the second a matter of adhesives. In neither case did the mating speaker suffer any damage within the same cabinet. On the other hand, when the first one went, it was an end cabinet in a row of four standing on end, side by side. I opened the chamber cover and found the driver to be moving as much as if it were still being driven. Talk about coupling!
?;o)
Al