You can't begin to gauge what a headphone or speakers will actually sound like based on a frequency response graph!
Actually, this is probably one of the more scientifically accurate statements on this thread. Yes, the frequency response graph will tell you a lot about the speaker, but if you are interpreting that graph with a 'flat is better' bias, you may be headed toward disappointment, especially with headphones. The human ear generally is understood to be able to detect from 20 to 20,000 Hz. However, that is only potential, and it does not tell you anything about sensitivity or the ability to differentiate pitch, which is far more narrow. And no, I am not going to state what those numbers are, because it literally is different for every individual. To make it even more fun, that sensitivity and ability to discern is related to amplitude, or volume. So depending on the volume you listen at,your individual auditory response, and tonotopic map characteristics, you may find that you want certain peaks and valleys in your cans. The only way to even begin to figure that out is to subjectively try different headphones with varying frequency responses, and get your individual hearing analyzed by an audiologist. Oh, and even that is a subjective test because it relies upon your conscious response for the results.
