Measuring speakers

You would need some sophisticated equipment and a suitible environment to replicate testing as done in the mag's.

As a pratical matter even if you could it wouldn't make much difference in actual use since the room and speaker placement makes a huge difference.

Buy a test disc and a Radio Shack sound level meter and use it to set up the sub's and integrate their response with the main speakers. Easier than doing it by ear.

Buy a test disc...

Or make one on your computer (if you have one). Freeware is available for both Mac and PC. Save your file to AIFF (Mac) or WAV (PC). Then burn your file to a CDR. You can make a disc not only for your sub to main crossover, but for testing your whole system as well. (or if you do not want to go through the motions, just buy one!)

I prefer to make my own because I can pinpoint any frequency I choose.