I've just got ATH-M50x headphones. I've tried them with this 22 kHz >> 8 kHz test (at the top of the page).
I can only hear the high frequency clearly after the voiceover says 17kHz.
I've tried the same test on basic home sound system speakers (they have tweeters) and I can clearly hear the sound after the voice says 18kHz and I can even hear a hint of a sound after it says 19kHz.
All tests were run on a Macbook Pro. I can hear 18k on headphones if I bump the volume real high, so the voice becomes deafening loud. Obviously there is big drop in amplitude at higher frequencies. While on speakers I can hear 18k at pretty low volume.
Headphones frequency response is rated as 15 - 28,000 Hz. Why can I hear higher frequency on average speakers and not on pro level headphones? What's the point rating them 28k if there is a big drop in volume at 18k?