Maine...You are ALMOST correct when you say "it's nearly physically impossible"...actually it IS physically impossible!!
There are no GOVERNMENT regulations for how power should be reported. There used to be for home stereos, but now even that is gone. As a result some companies measure to make their units look powerful...and the reputable companies begin to lose sales...so they start to measure the same way until you cannot believe anyone.
A couple of years ago the CEA came out with a STANDARD for testing of car amplifiers and if mfrs. would rate their radios this way then we could have some decent comparisons again...but even this standard is loose...and there is no public push for this so the battle of false specs continues. The CEA standard is often shown on quality amplifiers...but rarely on the radios themselves. Here it is:
CEA-2006 Compliant
On May 28, 2003, the
Consumer Electronics Association published standard
CEA-2006, "
Testing & Measurement Methods for Mobile Audio Amplifiers." This "voluntary" standard advocates a uniform method for determining an amplifier's RMS (continuous) power and signal-to-noise ratio.
Using 14.4 volts, RMS watts are measured into a
4-ohm impedance load at
1 percent Total Harmonic Distortion (THD) plus noise, at a frequency range (for general purpose amplifiers) of
20 Hz to 20,000 Hz. Signal-to-Noise ratio is measured in weighted absolute decibels (dBA) at a reference of
1 watt into 4 ohms. This applies to both external amplifiers and the amplifiers within in-dash receivers.
CEA-2006 allows consumers to be able to compare car amplifiers and receivers on an equal basis.
Manufacturers who choose to abide by the new standard are able to stamp their products with the CEA-2006 logo that reads: "Amplifier Power Standard CEA-2006 Compliant."
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For those interested in HOW they cheat in the wattage game, here are some of the ways:
-Wattage quoted is instantaneous peak not continuous power.
-One channel at a time is measured with all power available to that channel. (i.e. 22 watts per channel...but only one channel at a time...not 88 watts total)
- Distortion is measured at 10% rather than in 10th's of a percent or at most 1%
-Wattage is measured driven into a 2 ohm load rather than a 4 ohm load.
-Wattage is measured peak to peak on the sine wave rather than from 0
-Wattage is measured only at an EASY frequency (1khz) rather than over the full range of hearing (20-20000hz).
-Power is measured using a 14.5 volts source rather than 12.6 volts of a full battery.
Clever eh?