If I am going to get a 10" alpine type R sub and a 300watt amp, if the sub is 4ohm, then do i need an amp thats 300watts at 4ohm or 2ohm, the reason i ask is that I saw a picture in the manual for the alpine sub (4ohm) said that the amp should put out at 2ohm, if anyone could clarify all this im so confused...

 

Here's the rundown. The speakers determine the ohm load, and the manufacturer of the amp can tell you what the amp will put out at given ohm loads. Amps don't 'have' ohms, only speakers.

Roughly speaking, an amp's output will double every time the ohm load is cut in half. Say you have an amp that will put out 300 watts given a 4 ohm load. You buy two 4 ohm subs, hook them up in series for a 2 ohm load, then your amp will put out up to 600 watts (but probably a lot less.) As the ohm load goes down, though, the hotter the amp runs.

The Alpine amp should be 2 ohm stable. I would be surprised it it wasn't 1 ohm stable as well.