At some point in the past, certain power amplifier manufacturers got hip to the fact that the only specification most power amp buyers pay attention to is wattage.
Sadly, they decided that misleading specs were OK as long as it created better sales. Hmm….
For purposes of our discussion, let’s consider two amplifiers. Amplifier A is rated at 1,000 watts (per side), into a 2-ohm load, with .1 percent Total Harmonic Distortion (THD), measured at 1 kHz, while Amplifier B is rated at 1,000 watts (per side), into a 4-ohm load, with .03 percent THD, measured full range from 20 Hz to 20 kHz.
Let’s break this down, starting with load. All amplifiers, regardless of manufacturer, will provide more power into a 4-ohm load than into an 8-ohm load. Less resistance from the loudspeaker(s) will allow more output from the amp.
Similarly, the amp (if it will run at 2 ohms; some would rather not) will provide more power into a 2-ohm load than a 4-ohm load for the same reason: less resistance.
Let’s imagine you have four 8-ohm loudspeakers all running off of one channel of Amplifier A (which results in a 2-ohm load at the amp output, and most professionals won’t do this). Each loudspeaker is provided with 250 watts.
Now let’s look at Amplifier B. It delivers 1,000 watts into a 4-ohm load (the equivalent of two 8-ohm loudspeakers), so each loudspeaker is provided with 500 watts. An amp that will provide 1,000 watts into 4 ohms will typically provide about 1,600 watts into 2 ohms.
Therefore, each loudspeaker in the 2-ohm scenario is provided with 400 watts rather than the 250 watts cited in the previous example.
The moral of the watts story? “1,000 watts” isn’t necessarily 1,000 watts by some standards.
The breakdown continues: Amplifier A was measured at 1 kHz, while Amplifier B was measured full range, 20 Hz to 20 kHz. Full range (also called full spectrum) audio requires exponentially more power than a single frequency.
Liken it to a couple of Olympic shot-putters. They can both put the shot 30 feet, but the first guy uses a shot that weighs 4 pounds,while the second guy uses a shot that weights 20 pounds. Which guy is stronger?
In our case, the amp (Amplifier B) that puts out 1,000 watts from 20 Hz to 20 kHz is substantially more powerful.
The moral of spectrum versus output measurement? “1,000 watts” isn’t necessarily 1,000 watts by some standards.