Is this subwoofer active or passive?

http://www.carid.com/boss-audio/10-phantom-series-2100w-4-ohm-dvc-subwoofer-mpn-p106dvc.html

I'm buying things for my 2011 Honda Civic and I want to know if this subwoofer is active or passive. I need to know if I have to drop more money on any amplifier or not. Also I bought a set of 500w speakers as well. Do speakers alone make your music louder or is it the subwoofer alone?

An "active" subwoofer is one that is powered and comes with its own amplifier. This is a passive sub you're looking at. Speakers alone won't make the music much louder unless they have a greater efficiency rating and / or more power fed to them. Also, you shouldn't refer to peak power, you should always look at RMS power.

Anonymous is correct. An active subwoofer is powered by it's own amplifier, which produces more power than the rest of your stereo system. But he is incorrect about a speaker not making music louder, because a subwoofer with a bigger cone, is already using the same power as a speaker with a smaller cone, with more efficiency. He is partially right though. You should not use a subwoofer on a stereo/amplifier system that wasn't designed to have one in the first place. Subwoofers play subsonic frequencies, and need to have the higher frequencies (above 300hz usually) filtered out, or it will destroy the voice coil(s) on the subwoofer, because the cone/coil assembly weighs more, and the higher frequencies make it move faster, which creates more heat. And never look at peak power numbers. They're there to make the brand look good, and are almost always rated way way higher than what the subwoofer, or equipment in general will handle/put out. If it doesn't list RMS wattage, and list it before peak (shouldn't list peak at all, because you should never be reaching peak power, back away from it, because they're trying to make their product look better than it is. Peak power should never be considered, or reached. Peak, rated correctly is usually about 10% of total power higher than it can handle for more than a 30 second burp. If you have a 500 watt RMS/1000 watt peak subwoofer, don't power it past 800 watts for more than just a couple of seconds, because it will fry it. Until you get into big very high quality brands, you should never exceed RMS power.

The Boss sub is passive. It requires an external amplifier to operate.

Speakers alone can certainly make your stereo system louder (but they need to be driven with adequate power - often from an external amplifier). Many car stereo systems do not use subwoofers as a good 6x9 or 6.5" speaker can generally produce enough bass to have what can be considered a "full-range" sound system at low and moderate volume.

Subwoofers are low-frequency speakers. If you want good, loud full range speakers they will not be able to accurately cover low frequencies -- that is when subwoofers become a necessity.