I'll summarize the main points here.
- Headphones Sennheiser HD518 and Audeze LCD-2 rev 2 for chosen for this test, based on consistency of seal, low distortion, and extended frequency response.
- Measurements were made using a GRAS 43AG ear and cheek simulator, mounted on a Styrofoam manikin.
- Listeners were asked to rate each headphone after equalization to a number of different target response curves.
- Two of these curves, RR_G and RR1_G, were created by measuring the in-room response at the listening seat of Harman's 7-channel, 4-subwoofer listening room. The RR1_G curve was based on an in-room response that, when measured using a regular microphone, is basically a straight line that slopes downwards with frequency. Such a response was favored in subjective experiments in loudspeaker listening. The RR_G curve corresponds to a straight horizontal line, except with a bass boost. For reference, here is the measured RR1_G curve (black line) as measured on the Audeze.
- Test using Audeze LCD-2 showed that the RR1_G response was by far the most preferred, over RR_G, no-EQ, diffuse field, and free field curves.
- Tests using Sennheiser HD518, which did not include RR1_G, showed that the RR_G response was by far the most preferred.
- Though the headphones were tested in separate tests so I'm not sure how comparable scores are across tests, I do note that HD518 equalized to RR1_G had a higher rating (5.85 vs 4.08) than an unequalized LCD-2 (!).
- From the paper's Conclusion: "....a headphone target response curve that approximates the in-room response of a calibrated loudspeaker produces a higher quality of sound reproduction [than diffuse-field and free-field] that listeners prefer."
Big big kudos to the researchers, as well as Harman for publishing this research. Audeze and Sennheiser take note! Harman just published some free research very pertinent to your interests!