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?