This is yet another IEM received from Inks. Once again, thnx for giving me this opportunity, my friend. Please keep in mind that the listed reference response has been obtained with gray filters attached.
CON: There is a lot of harmonic distortion, especially the third harmonics, in the mid-range, at which the human hearing becomes the most sensitive. This is definitely audible, and seems due to the over-equalization done by the manufacturer to forcibly meet the target response. Well, I guess it is a reasonable compromise to take for the low price.
ON SECOND THOUGHT: Although PFE 022's accuracy is right on the target, its practical insertion depth is little too shallow due to the stem being too short. The owner, Inks, also notes that its sound is slightly harsh for him. The magenta-coded plot on the right shows the response with PFE 022 inserted shallow. No wonder it was harsh.
The response of PFE 022 can be tamed, by using filters with various acoustic impedance value. If I was the owner, I'll just stick with gray filters, since they yield the least peaky response.