Usually all speakers are set to "small", and the crossover is set to 80Hz
If you can post the model of your speakers and receiver; to get more sugestions it will be better.
Is your receiver capable of doing an Auto Calibration??? ... if it can, start with that, and then manually adjust the set up if the speakers were set to large change to small, if distance is incorrect fix it and crossover if necesary.
If you have to do it manually (no auto calibration) ... check your speakers, specially the minimum frequency response (eg. L + R
35Hz - 20Khz, Center
50Hz - 20 Khz, Surrounds
120Hz - 20Khz, etc) then set your crossover to the highest minimum frequency (in this case 120Hz)
Hope this helps
