I read in "Handbook of Acoustics" by Alton Everest

A famous acoustician, Harvey Fletcher, found that playing pure tones of 168 and 318 Hz at a modest level produces a very discordant sound. At a high intensity, however, the ear hears the pure tones in the 150-300 Hz octave relationship as a pleasant sound. We cannot equate frequency and pitch, but they are analogous.

I try to reproduce it but I can't. (tuning two sine waves to the said frequencies and listening at low and high level). For what intensity this phenomenon takes place? Is there a table that presents the change of perceived frequency and the gain?

From the article about Fletcher–Munson curves at Wikipedia:

The article also comments on the large differences apparent in the low-frequency region, which remain unexplained. Possible explanations are:

The equipment used was not properly calibrated. The criteria used for judging equal loudness at different frequencies had differed. Subjects were not properly rested for days in advance, or were exposed to loud noise in traveling to the tests which tensed the tensor tympani and stapedius muscles controlling low-frequency mechanical coupling.

Is the reference accurate?

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    $\begingroup$ Does Everest give a citation for Fletcher's work? Or have you found one yourself? That is the canonical way to find out what Fletcher actually did. $\endgroup$ – rob Aug 7 '18 at 11:13
  • $\begingroup$ @rob I checked the reference at the 4th edition (I have the 3rd here in translation) and the reference is there. Thanks, I investigate the issue now. $\endgroup$ – user92450 Aug 7 '18 at 11:21
  • $\begingroup$ If you edit the citation into your question, another user might have some insight. The passage you quote from Wikipedia seems to be about measuring the subjective loudness of low-frequency pitches, but the passage from Everest seems to describe some kind of nonlinear frequency-shifting effect. $\endgroup$ – rob Aug 7 '18 at 15:45
  • $\begingroup$ @rob I tried another experiment from the same book (sum and difference of a 23 and 24kHz in the non-linearity of inner ear) and couldn't make it work either. For me poor selected and non reproducible experiments. I give up the book, and everything I read should be triple checked for whatever reasons of exaggerations. Discordant chords that become consonant in high levels is just nonsense. $\endgroup$ – user92450 Aug 7 '18 at 17:30
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    $\begingroup$ @rob In this answer physics.stackexchange.com/questions/407836/… the experiment seems to be quite subjective and it does not worth to be described as an accurate phenomenon. (as in the handbook I mentioned) $\endgroup$ – user92450 Aug 7 '18 at 17:39

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