The peaks are caused by the interaction of headphones and ears. It happens with every one of my headphones, always in the 2-3khz and 7-8khz range, dependending on which headphone im using.
Here is a quote from the EQ thread:
"I just performed a very interesting test. I put my headphones down on my desk, and turned SineGen up to its loudest output. I ran through the entire frequency range, and as far as I can tell, my headphones have a nearly perfectly linear frequency response. It is only when I actually put them on, so that the transducers are closely coupled with my ear canal and eardrum, that the frequency response becomes uneven."-piccolonamek
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