I am talking about "cumulative" bass distortions. Not a single tone distortion. For example, add all distortions from the bass notes, for example 20 to 200 hz,
I am not sure what you meant by "cumulative" bass distortions. THD is already the "cumulative" in a sense, so if at 1000 Hz, THD is 0.005%, that 0.005% would represent all of the harmonic distortions, i.e. 1000,2000,3000,4000,5000,6000,7000,8000,9,000,10,000...........................20,000 Hz and higher.. When you say "for example 20 to 200 Hz", that really doesn't apply to amplifiers because the amplifier will see whatever voltage is applied to its input at any particular instant and amplifies it. The signal may represent many tones but to the amplifier it still one varying voltage, one value at a time, and the total harmonic distortions in dB or % represents the distortions reference to the magnitude of the fundamental frequency, one frequency at a time, not over a range of frequency. THD 0.08%, 20 to 20,000 Hz simply means THD over the 20 to 20 kHz range does not exceed 0.08%. I am sure you know that but again I just want to understand more clearly what do you mean by "add all distortions from the bass notes, for example 20 to 200 hz". May be you can clarify it with a numerical example?
If you look at the FFT of the AVR-X3700H to see the individual harmonic distortion instead of the "Total/cummulative" harmonic distortions, the 2nd harmonics + noise was the highest but still only -95 dB vs the Total harmonics distortion plus noise of about 88 dB if you plug that into solderdude's calculations you will see that it would hardly be a factor. As he said, in his example he picked the amp with the worst THD+N on the ASR chart.