Strings are part of the equation - B strings are typically too thin in gauge to match the rest of the set. And you won't easily find a cabinet that'll do a B string justice. Most bass amps don't even cover a low E that well. I have speakers that I built to go down to D (I'm an Acoustical Physicist, so this is kinda normal stuff for me, and D is as low as I tune my basses). The cabinets are about twice the physical volume you typically see for bass guitar cabinets - they look a bit huge for the drivers you see in them, but....they work. Most bass guitar rigs are designed to fit into cars and such, not for optimum acoustical performance - people just don't want speakers that big. I have a small SUV, but I'm not sure if I desinged speakers to truly cover a low B, if they'd fit in the thing. Probably not.