The basic premise of a mob spawner is to generate mobs and then kill them for drops. In modded Minecraft this is often an automated process and can be done using a variety of methods.
Within 24 blocks (1.5 chunks) no mobs will spawn. 24-32 32 (2) -128 (8) 128
ExtraUtils spike designEdit
MFR grinder designEdit
One design which I've often used in the past includes a ComputerCraft melee turtle running an atack loop.