Cabs and speaker surface area

[Pow_22]

My current cab is an early Barefaced 1x15 compact - lovely cab, very easy to move and a superb sound.  However, ive been trying to get away with using an Ashdown Little Bastard head live as we do use a decent PA and all DI into the mix but finding it falls JUST short.  I have the opportunity of a dirt cheap Ashdown ABM 4x10 (UK made, blue speakers) and was wondering what the volume difference would be from a 1x15 to a 4x10 (im very much aware of the limitations of a 30w head).  I know Barefaced are supposed to be super efficient so that further muddies the water as to exactly how much more volume a 4x10 box would throw out?

Edited 2 hours ago by Pow_22

[Bill Fitzmaurice]

Surface area by itself means next to nothing. What matters is area x excursion, ie., displacement. BF lists it, Ashdown doesn't. In any event you're not going to get anywhere near what the BF you have is capable of with 30 watts. 300 would be more appropriate. 

[Dan Dare]

Bill's correct. I think the blue Ashdown drivers were Sicas, so were of reasonable quality. However, the BF is a far superior design and will certainly be more efficient (and therefore louder) than the Ashdown. I'd put the money towards a more powerful head, rather than throw it at another cab, no matter how cheap it is. 30w is really only adequate for home, studio or acoustic gig use for a bass. Guitar players can get away with 30w amps on gigs because they do not want clean sound or extended low frequencies, both of which need power.