So, as measurements are showing chances are your listening room is, as mine is, flooded with 35-40dB of noise, if not more. That means that even 1% THD will be effectively burried into the noise floor. But speaking of famous THD/IMD, let me quote what Dr. Toole is saying about it in his book:
"Thus began the legend that harmonic distortions are relatively benign and intermodulation distortions are bad. It is true in the context of these test signals, but they are both simply different ways of quantifying the same problem (the nonlinearity in the loudspeaker), and neither test signal (one tone or two) is even a crude approximation of human voices or music. Contributing to the mismatch between perception and measurement is the fact that such a technical measurement totally ignores masking. Included in the numbers generated by the measurements are distortion components that, to humans, are partially or completely masked. The numbers are wrong. The end result of this is that traditional measures of harmonic or intermodulation distortion are almost meaningless.
They do not quantify distortion in a way that can, with any reliability, predict a human response to it while listening to music or movies. They do not correlate because they ignore any characteristics of the human receptor, an outrageously nonlinear device in its own right.
In loudspeakers it is fortunate that distortion is something that normally does not become obvious until devices are driven close to or into some limiting condition. In large-venue professional devices, this is a situation that can occur frequently. In the general population of consumer loudspeakers, it has been very rare for distortion to be identifi ed as a factor in the overall subjective ratings. This is not because distortion is not there or is not measurable, but it is low enough that it is not an obvious factor in judgments of sound quality at normal foreground listening levels. "
And that's pretty much it, I left a few paragraphs not to make post too long. So, in a book of 540 pages there are only 2 pages about distortion. Add that to the fact that spinorama charts also doesn't involve distortion and you got the picture of what THD/IMD figures really mean to our ears. Hopefully.
