"And the wonderful thing about standards is that there are so many of them."
That's a really old quote - and one that doesn't particularly come from the audio industry.
The point, however, remains the same.
"A standard" is simply a description about how to measure something, do something, or describe something, which some group of people have agreed to use.
Some standards have the force of law... which means that some government or government agency has agreed to require people to use them.
For example, we can at least hope that, if our local gas station decides to start charging you based on their own private idea of what "a gallon of gas" is, and pick something different than "the standard gallon", they will get in trouble.
To quote one of the sites that offers to sell copies of the publication about CTA-490:
"This revised Standard reflects the current consensus of the members of the Institute of High Fidelity "
And, from their web page:
"The Institute of High Fidelity, Inc. (IHF) is basically an association of manufacturers producing equipment for recording and reproducing music........."
and "In addition, certain publishing companies which regularly publish articles on equipment and techniques for sound reproduction in the home are also members of the IHF."
In other words, it is the official opinion of the vendors who belong to that organization, that this is the best way to measure audio equipment.
I encourage anyone who is really interested to look up the member list for that organization....
And decide for yourself if you consider their opinion on the subject to be "the definitive last word in everything you need to know about your audio equipment".
(If you do, and consider it to be more useful to you than the other standards, established by other groups, then you should seek products that have been tested according to this one.)
I apologize for making fun of the situation...
And, yes, a standard at least offers a means of comparing things on equal footing - at least inside the narrow context of the standard...
However, in this particular case, it is also true that virtually all loudspeakers are in fact highly reactive loads...
Therefore, while testing every amplifier according to a single standard, using a nice simple resistive load, would in fact make it easy to compare them...
There is also a fair argument that it wouldn't tell you much about how any of them would perform when you actually connect it to a speaker.
The "power cube test" is probably the most inclusive and informative way to test amplifiers.
However, it is almost certain that there are three basic reasons it was never widely used:
1) It is actually somewhat complicated to perform and requires more specialized and expensive equipment, and more time, than other simpler tests.
2) Some amplifiers would undoubtedly perform quite poorly on that test.
3) Even worse, because the test and the results are complicated, very few consumers would understand how to interpret them correctly or usefully.
An amplifier that performed well on that test would almost certainly perform well with any speaker (at least in certain ways).
However, designing an amplifier that performed very well on that test would also require extra effort, and producing it would cost more.
Therefore, for many people who don't require it, it would raise the cost of their equipment, and force them to pay for performance they really don't need.
(If a certain amplifier performed poorly on a certain small portion of the cube, most consumers wouldn't know enough about their other gear, and so wouldn't know if that would affect the performance in their system or not.)
(This would encourage manufacturers to design amplifiers that had capabilities nobody actually needed.... which would cause prices to go up...)
A simpler and more useful "standard" would probably specify testing an amplifier with several specific reactive loads - each designed to represent certain common types of home speaker systems.
That way each customer could at least hope to learn which result was most representative of how the product would act in their system.
(And could ignore the portions of the results that don't apply to them.)
A few magazines have attempted to create such test standards in the past - with little success.
However, as usual, the reality is that no such "widely accepted standard" currently exists.....
(At least not for amplifiers used in surround-sound gear.)
Which puts us right back where we are now...
Look up CTA-490. OrCTA-2000 for mobile amps. And your obsession with reactive loads is moot. A standard is a standard.
Sort of off topic 
