Originally Posted by SoCalGuy-99
How many internal channels was this driving at -10dB?
Because it's interesting with No Source playing (Zero output) and Eco-Off, the power = 92W yet when playing a Source at -10dB and Eco-Off, the power = 97W which is only a 5% increase from Zero output (No Source playing). Do the A/B amps really get that much more efficient when running near full power or does it really only take an extra 5Ws to go from Zero output to -10db on the AVR's volume scale?
It's not THAT surprising if you know that JD is using higher sensitivity speakers and you understand the logarithmic nature of power demands, and average vs peak levels (I'm assuming these tests were done with normal content playing not brief full scale peak content).
Reference level is set at 85dB for dialogue, avg levels are a bit higher since there is a lot of non dialogue stuff happening in most scenes, so let's call it 90dB. If you're at -10dB volume, then that's ~80dB.
A 90dB sensitive speaker by definition puts out 90dB with ONE watt of power at 1 meter distance. If you're sitting 10-12' away, you may lose ~5dB to distance, so let's guesstimate 85dB at the listening position with ONE watt of power. So even with a relatively active scene (let's say 95dB avg levels at reference = 85dB at -10) you're still using at most 1 watt of power per speaker, and the surrounds are likely using far less. And you're bass managing the most power hungry low frequencies to the subs, so the load on the AVR amps is reduced even further. So even if conservatively the LCR are using 1 watt each, the other 5-8 speakers are likely using a few tenths of a watt each.
When you look at it that way, in a typical sized room with 10-12' listening distance and 90dB+ speakers, unless you listen close to reference level the system is just loafing along barely above idle with the majority of content. Content at 80-90dB SPL sounds pretty loud but it's using barely any power at all.
Where power becomes an issue is PEAKS, especially if you listen louder than -10, and especially for the deep bass where LFE has a 10dB boost and more power is required to drive those long wavelengths. Power demands go up 10x for a 10dB increase. So that 1 watt to produce 85dB becomes 100 watts to produce 105dB -- the 20dB headroom for dynamic peaks translates to 100x the power. And that power must be available for quick bursts so the amp is going from easy idle to full blast over the span of a few milliseconds.
That's why headroom is important, because if the amp is maxed out at 100 watts it's not going to be as "clean" (distortion / harmonics / clipping) as an amp that can sustain a peak burst of 300 watts. A lot of people recommend at least 3dB headroom above peak output, which equates to at least 2x power headroom, so that 100 watts is now more like 200+ watts if you want the amp to not be breaking a sweat when that massive explosion kicks in. A lot of people don't realize their peaks are getting clipped/distorted until they hear a system that can reproduce those peaks cleanly.
So the bottom line is, because of the logarithmic nature of amplifier power, and the 100x power demand for peaks, you generally don't need much power at all until suddenly you *really* need it.