The best way to tell if an amplifier's rating is b.s.

[POS carb]

Pissed off rant... looking at all these amps on ebay is getting on my nerves.

Best way to know how powerful an amp is: Just look at the fuses........
example:
http://www.ebay.com/itm/SOUNDSTORM-E...item5192d96a6e

This amp claims an output of:
2500 watts RMS at 2 ohms
1000 watts RMS at 4 ohms
however, it has 2 25 amp fuses!
so... if power = voltage x current then 14.4v x 50a = 720 watts max consumption (347.22% efficiency).
If the amp was 100% efficient (which is impossible) the most you could get out of it is 720 watts.

As a comparison, the class D Cerwin Vega EXL1200D I have in the Accord claims:
1200 watts RMS at 1 ohm @ 0.05%THD <-(THD is also important)
it has 4 30 amp fuses which means 14.4 x 120 = 1728 watts max RMS consumption (69.44% efficiency)

FYI
Be an informed consumer.

[RAZR]

well for starters dont buy that amp!

If u want to read peak watts on ur amp. Take a volt meter and put it to AC current and put the two leads on the + and - of ur amp. put on a song that bumps and take the highest reading u get. now multiple that number by itself and divide by you impedence and thats your peak watts.

[RAZR]

Most lower dollar amps claim bug number but most will not put out that much.

[charliekuney]

o:

[DBMaster]

^x2. Just like with the wattage ratings on speakers. How high can you turn up the volume before all you hear is a bunch of loud distortion? I did take circuit analysis and physics in college, but I don't want to take a refresher on signal/noise ratio and total harmonic distortion. There is a lot more to a great sounding system than the numbers on a box.

[cygnus x-1]

Wattage is kind of a bogus number. Unless you know how it was measured/calculated it doesn't mean anything. It's a measurement of energy output over time. So if you only measure the energy output for a very short period of time, like 1 millisecond, it's easy to get a huge power number. Looking at the fuses is a good sanity check.

C|

[lostforawhile]

if it's a quality brand amp and the power is showing into rms at 4 ohms, it's probably right, most quality stuff doesn't have to overstate it's output, because the consumers buying it are pretty informed anyway. Most of the huge bogus numbers on amps are aimed at the guys who drive down the street rattling their trunks, and wouldn't know quality sound if it bit them in the ass

[Hauntd ca3]

when i look at buying an amp, i look at the wattage rms at 12 volts and 4 ohms and what the total harmonic distortion is at that given out put.
any more than 1% thd and you will hear it.
most cheap manufacturers claim output at 5 or 10% thd which will sound like shite.
my old sony amp i have had for years was rated at 0.01% thd

[import racer]

Yeah having bass is one thing but I like to hear the mids and the higs as well.Not wanna just hear boom boom ,not to mention that you're vibrating all the bolts loose in your car.I remember back in the 80's all that phase three pyramid junk floating around with really high ratings.

[Dr_Snooz]

If you value good sound, why are you shopping for amps on eBay? Numbers are a pretty bad way of choosing amps. Ears work much better. I wouldn't buy anything I didn't put a stack of CDs through.