CFO (Chief Fun Officer)
- Feb 13, 2016
- Seattle Area
Note the LCD-X have a distortion minimum right around the frequency tested here, 40 Hz, so this result may be under-representative of their average distortion across the rest of the frequency range. See Innerfidelity's distortion measurements of them here:
As you see, there is no dip at all at 40 Hz. It wouldn't make sense to have a dip in distortion anyway. But rather, you are falling victim to misleading way THD percentage works in systems with varying frequency response like speakers and headphones. There, the amplitude changes and that causes THD% to vary even though the distortion mechanism itself does not. Here is Tyll's frequency response test that shows this:
Notice as I circled, his measurements show sudden increase in response around 40 Hz. So for the same distortion amount, the percentage will shrink.
In my testing I am using a single tone @40 Hz and assuring that the identical reproduction level is used in both headphones. As a result, frequency response variations are dialed out and THD ratios can be compared.