What do the watt numbers mean on 2 channel amplifiers?
There is no standard in advertising, so it could be either. You need to look at the specs on the individual amplifier listed in the owner's manual. This can also usually be found on most websites like Sonic Electronix or Crutchfield. Be aware that amplifier ratings depend on the testing procedures used. The better companies adhere to an international standard known as CEA-2006 that allow you to compare different amplifiers more accurately. The cheaper manufacturers don't adhere to this standard and their ratings are typically over-inflated by 2-3 times. RMS output is a measure of power that can be thought of as a maximum continuous output at which distortion is below a certain amount, so even when comparing ratings on equipment that comply with the CEA-2006 standard, it's a good idea to look at the level of distortion present at that rating. Distortion of 0.1% at 1000w rms wouldn't be noticeable, while at 3% would be pretty bad. Keep in mind that you can't listen to music at full output from a powerful system without hurting your ears, so at a lower volume setting the distortion may be inaudible. (note: distortion can easily destroy speakers) A very general way to tell if the power rating is in the ballpark of being realistic is to multiply the fuse rating times 13.8 volts (the average voltage output of an alternator). So lets say the amp you are referring to has a 35 amp fuse on each channel. 35 amps x 13.8 volts = 483 watts. That is the highest power output beyond which the fuse will blow to protect the circuitry from overheating and catching fire. Most fuses on amps are of the "slow blow" type so transient spikes above that value won't automatically trip the fuse, so in this case the amp might be rated 500 watts rms per channel. .
It would be helpful if you'd just provide the brand and model, then we can explain exactly what you're looking at. If it specifically states 1000w rms x 2, then clearly it's supposed to mean 1000w to each channel for 2000w total. However -- a 2 channel amp that powerful would be rare and expensive. Almost every amp capable of 1000w+ rms is a single channel (mono) subwoofer amp. On the other hand -- there's no shortage of junk brands pushing ridiculous "ratings" to sell cheap amps since there's no oversight regarding advertised vs actual power. The best indicator is price. A 2000w amp is generally going to be ~$250 at cheapest. There is one amp I know of right now that will do right around 2kw for $215. That is a rare exception. Many quality ~2kw amps are $400+ Also -- for actual power approximation -- don't mess with 13.8 (typ electrical system voltage). Just use 10. 1) You can do it in your head. 2) It accounts for inherent losses in the process and is generally more accurate than using battery voltage.
That means that the amp can produce up to 1000 rms watts on each channel when playing into a speaker with a 4 ohm impedance.