deludedaudiophile "You can't compare the frequency response of a headphone to speakers."
You most certainly can and in fact should make such comparisons and they are valid, meaningful, and useful in determining and establishing the relative accuracy of not only each other but the recording itself which is why you will find in many recording studios and other recording environments that both speakers and headphones are used for judgment and evaluation of the work underway.
I suggest you familiarize yourself with these common practices so as to avoid your misinformation.