not at all, it all depends on how low of ohm stability your amp can handle. And then what ohm load you put to it. Your ohm load is determined by how you wire your subwoofers. You could hook a few speakers to a Mono amp if you want if you wire them correctly so they work.
Check out this crash corse from our buddys at adire.
http://www.adireaudio.com/Files/TechPapers/DualVoiceCoilWiring.pdfor for non-descriptive wiring diagrams check out this one
http://www.rockfordfosgate.co.za/rockford2002/tech/wiring/wiring.htm 
