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 yesterday at 15:42 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.

[itu]

2 hours ago, Dan Dare said:

...because they do not want clean sound or extended low frequencies, both of which need power... 

...and their playing happens at the ear's most sensitive frequencies. 

[Bill Fitzmaurice]

To put that into context for the same output level you need at least twice the cone displacement with bass as you do with guitar. To realize twice the displacement requires double the voltage swing, which is four times the power. You may need as much as four times the displacement, which is four times the voltage swing, which is sixteen times the power. 

[itu]

30 W x 16 ≈ 500 W

QED 

[Downunderwonder]

It would have to ge a real rubbish 410 to fail to make more out of 30w than the BF 115 cab.

 

Still not a sensible swap. Lugging a hulking 410 and losing dispersion for a measly volume bump is not my idea of upgrades.

[Dan Dare]

8 hours ago, Downunderwonder said:

It would have to be a real rubbish 410 to fail to make more out of 30w than the BF 115 cab.

 

Not necessarily. It's not just about outright volume, but about where that volume happens in the frequency range. You need excursion, as Bill notes, to reproduce low frequencies at high level. You also need a well-designed cabinet that makes the most of the output from the driver(s). A properly ported cab' like the BF will do this better than a plain box like the Ashdown. 4x10s tend to be sealed boxes with drivers wired series/parallel - less efficient than ported designs and with less bass extension.

 

If you look at cone area, with drivers of the same efficiency, a single 15 has more cone area than two 10s (176 sq in vs 157 sq in). So if that 15 has twice the excursion of the 10s (especially in a well-designed cab'), it will be louder and have better bass output than four of those 10s, because it can shift more air. If the 15 is more efficient than the 10s, the difference will be even greater.