Subs up for more bass

Getting a good kick drum sound on a gig many engineers would agree, is a factor of how good your subs are.  A pair of 15in drivers is not really going to cut it unless it's a really small gig.  Horn loaded 15s or band pass 15s maybe!  A key fact to consider is this:- to double the perceived volume you'll need to need to more than double the power.  In fact, you'll need around 10 times the power to double the volume (a 10dB increase).  So that's like going from your 1KW system to a 10KW system.
But there is another way... doubling the number of subs will generally increase  your bass output by 6dB.  So let's say you take your 1KW rig, and instead of 1 15 inch sub each side, you put 4 15inch subs each side.  You will have more than doubled the bass output.  For the same power!  I'm assuming your amp will cope here, by the way... It may be asking a lot to go from an 8ohm load per side to a 2ohm load per side with 4 cabs a side connected.  I've blown amps up using them like this in the past.
But what about the mid range and high end?  Yes, you can gain around 3bB each time you double the number of cabs on the high end.  But you'll need to watch out for comb filtering, and lobing.  For small(ish) events, sometimes just pumping up the bass with more cabs can be enough, if you've got good quality tops.

If you are interested in hiring sub-woofers, have a look at my website here: www.soundtruth.co.uk