What is the importance of an amps efficancy?

I know being effeciant in anything is good, but how does this affect amplifier performance when comparing apples to apples.

If you have one amp that is say 90% effeciant at 4ohms and another amp that is 70% effeciant at 4ohms and are both rated to put out 500 watts at 4ohms at 12.8 volts; what does the effeciancy rating tell me, the consumer, about the amp I am using?

Any input would be appreciated.

What is the importance of an amps efficancy?

I know being effeciant in anything is good, but how does this affect amplifier performance when comparing apples to apples.

If you have one amp that is say 90% effeciant at 4ohms and another amp that is 70% effeciant at 4ohms and are both rated to put out 500 watts at 4ohms at 12.8 volts; what does the effeciancy rating tell me, the consumer, about the amp I am using?

Any input would be appreciated.

Well it comes down to power draw mostly. The 90% efficient amp is going to take less current (amperage) than the 70% efficient amp will to produce the same wattage. The 90% efficient amp will draw ~43.4 amps at 12.8 volts to produce 500 watts and the 70% efficient amp will draw ~55.8 amps to produce 500 watts at 12.8 volts. Music is dynamic though, so it will vary. But the point is that the 90% efficient amp is going to take less power to produce the same wattage as the 70% efficient one.

Thank you!!

Keep in mind efficiency is not a fixed value. An amplifier's efficiency will vary based on power output at a given impedance. For example, class A/B amps are significantly less efficient at 1/3 power (i.e. 33w on a 100w RMS amplifier) than they are at full power. Generally they are only around 30-35% efficient at 1/3 power even though they can be 60%+ efficient at full power output. Class D typically do not experience that dramatic decline in efficiency with power output. And as mentioned, music is dynamic. Your amplifier will spend much more time in the 1/3 power range than it will at full power. Which means that even though two amplifiers may be the "same efficiency" at full power, one amplifier may actually draw more current from the electrical system throughout the rest of it's power band (i.e. like while playing music).