Benefits of V loading drivers in subs?

There will be a trade off between the volume of air in front of the driver vs. having a larger rear chamber (for the same external dimensions).  With the right driver, a larger rear chamber could increase low frequency response.

In line with other comments, I did measure some gain at the upper end of the response, probably from 80Hz upwards.  It does also make the cabinet stiffer, reduce internal resonances etc.  Therefore I think that there are benefits to doing it if you are building more of a general purpose bass cab, especially if you intend to use it above subs and/or with a relatively high crossover point.  I used to run mine up as high as 160Hz sometimes for dance music which did give a decent 'kick'.

My view on the physics is that it increases the effective radiating area from being just the two circular drivers to the whole of the front of the box. Since we know that cone drivers just acting on the air directly in front of them isn't particularly efficient (hence why we use horn loading), anything that can improve that efficiency or you could view it as acoustic impedance matching is unlikely to be a bad thing.

Here is the response for the SB1001 which was the later generation of their dual 18" v-baffled box.

We can clearly see the effects of the cavity in both the FR and Z curves. 

As ceharden pointed out a couple of posts upthread, the main acoustic benefit would be if you wanted to use a higher then normal crossover.

Cheers,

David.