To add to this comment (to the readership and not Amir), in the dream world, we'd wave a magic wand and we'd have measurements at 0.05, 0.5, 5 and 50 watts for every amplifier that's tested. It'd give us a lot of information about the amplifier in a wide range of conditions. The reality is that it'd be impossible to get through any meaningful number of tests, so picking 5W is the ideal "single" measurement for the amp if that's what you have.
I would respectfully add more commentary to Amir's second comment given the wide range of differences in size of the "average real-life" listening environment. Millionaires living in New York City are going to have a different listening environment that a "blue collar, middle class worker" in the US midwest.
Looking at 3 highly-rated passive speakers here, we can see different levels of efficiency.
- Revel PerformaBe F328Be - 91 dB/2.83V
- Focal Aria 906 - 87 dB/2.83V
- Elac Uni-Fi 2.0 UB52 83 dB/2.83V
Then looking at the US, France, and Germany (for those speaker brands) and China (picked due to the popularity of Topping and because it's got a smaller average home size), we can see the average home size is very different which also translates into the average "living room" or "bedroom" [Ref:
https://www.homedit.com/average-bedroom-size/]
- United States: 2163 sq ft
- France: 1205 sq ft
- Germany: 1173 sq ft
- China: 645 sq ft
We need to pick listening distances. I have chosen 5 feet and 15 feet. 5 feet because that's the Dolby Atmos "minimum" distance for those upfiring home speakers. I've chosen 15 feet since that's my own listening distance in my biggest room in the United States. The 3x spread is pretty close to what we see in size difference between China and the US so it seems reasonable on face value.
Now the question is "what is the average listening level?" THX Reference Movies are
85 dB average. That's pretty loud because that's the upper limit of what you'd be allowed to listen all day/every day without injury. Then, I'll pick
65 dB for the lower level since that's the typical volume of someone sitting and playing the piano normally:
[Ref
https://music.eku.edu/sites/music.eku.edu/files/ekuhealthandsafety.pdf]
Now we do math. I will assume 2 speakers, near a wall.
Speaker | dB at 0.05W (5 vs 15 ft) | dB at 0.5W (5 vs 15 ft) | dB at 5W (5 vs 15 ft) | dB at 50W (5 vs 15 ft) |
Revel PerformaBe F328Be | 80.3 / 70.8 | 90.3 / 80.8 | 100.3 / 90.8 | 110.3 / 100.8 |
Focal Aria 906 | 76.3 / 66.8 | 86.3 / 76.8 | 96.3 / 86.8 | 106.3 / 96.8 |
Elac Uni-Fi 2.0 UB52 | 72.3 / 62.8 | 82.3 / 72.8 | 92.3 / 82.8 | 102.3 / 92.8 |
Peak advertised power handling
Speaker | Peak Advertised Power Handling | In room Peak SPL (5 vs 15 ft) |
Revel PerformaBe F328Be | 300 watts | 118.1 / 108.6 |
Focal Aria 906 | 120 watts | 110.1 / 100.6 |
Elac Uni-Fi 2.0 UB52 | 140 watts | 106.8 / 97.3 |
The detail that's missing from this is the concept of bass needing power. If we look at the Revel PerformaBe F328Be, the 30-50Hz region is ~81 dB/2.83V and impedance is about 6 ohms. At 50 Hz exactly, it's 84 dB/2.83V and 8 ohms. If you wanted your bass to hit 105 dB peaks at 15 foot listening distance, you need ~1300 watts into 6 ohms or ~650 watts into 8 ohms using those assumptions. (Hence, the value of a subwoofer even with full-range speakers.)