My bass tips:
1. Make sure your midrange is big enough to handle your subs, and don't run sub levels too high over your mains. It makes your system sound like mud, not crunchy like it should.
2. Add limiters so you never have to worry about clipping an amplifier (Unhook your speakers, play pink noise, turn up the gain until the clip light just begins to flash on the amp, then back it off a notch and set the limiter there with a hard knee). Limiters should be on full time, especially if you've seen the threshold light hit on the limiter ever and your power goes off a lot (storms and such).
3. Add limiters so you never have to worry about mechanical excursion problems (if you ever hear a subwoofer make a funny noise, lower the limiter threshold). This is different than where your amplifier clips, it may be higher or lower. The lower of the two is where the limiter should be set.
4. If you feel you need more output, high pass. The extra 5Hz of extension costs you a lot in power and excursion, it's not linear. If your pushing your subs, raise the low cut until they aren't being pushed too hard anymore. 15Hz is only cool if you can do it loud and can still do 50Hz loud (which is more what matters). Power and excursion are limited, choose where you want them wisely.
5. Always run stronger subwoofers than you need. This is true for all speakers, but if you can go overkill, do it. Subs always sound best when they aren't working hard.
6. If you have to make a choice between flatter response placement or better blending placement, choose the place that blends with the mains better. Blending is really hard to process, but flat frequency response can be EQd, and since you have followed tip 5, you have enough subwoofer to fill any little dips.
Try and get a happy medium, but the magic is when your mains blend with your subs as best as possible, so that you can let your midrange PUNCH you while your subwoofers PRESSURIZE you.
