Hinted at it here and just realized I never posted them: As you can see, the driver is resting on my coupler. For this measurement the material sat on plastic box, so there's a hard plate behind it. Might be interesting to repeat these measurements, but with only air or a very soft foam behind the material. I would also like to measure the driver from some distance like you would measure speaker drivers. Ultrabike posted such a measurement a few days ago, but of the whole headphone and not the driver itself. I think we should get more "raw driver" measurements of headphones. Maybe we should start measuring the headphones themselves in free space like the old stereophile measurements? But I'm not sure how well that would work. It seemed pretty difficult to get good results with the HD800 this way, but the HD800 driver seemed to be more linear than the HD600 driver (which seemed bumped up around 3-4kHz). BTW (if I wasn't clear enough on that before) the HD800 driver has extremely awesome CSD measurements with no hint of ringing at 6kHz (or any other frequency in the audioband for that matter). I mainly did these measurements to confirm that the HD600 driver has a resonance at 5kHz. It also has a resonance at 12kHz and at 24kHz. The green line is the driver resting directly on the material (as pictured). The red line is the driver on its back, resting on the black plastic cage. The blue line is the driver resting on a 2cm thick foam. I used a very thin foam that doesn't absorb a lot of HF energy. Here's what the CSD looked like for the driver resting directly on the coupler: I know the 12kHz resonance looks horrible, but it's actually pretty benign with more distance to the driver. It's not very bad with the actual headphone on a coupler or on a head. The slow decay on the left is simply how the bass rolloff affects the CSD visualization. That doesn't mean shit. Apart from the resonances at 5 and 12kHz the decay is very clean. I think the HD600 driver itself actually has more treble energy from 5-7kHz than the HD800 driver which just goes to show that there's much more a headphone than its drivers. The HD600 driver also has a rising response from 12kHz on up to its 24kHz resonance. When I put the headphones at some distance from the coupler, the HD600 CSDs never look as clean as the HD800. I will probably post those measurements soon. I wouldn't try to use headphone drivers as tweeters for speakers, even if the HD800 driver is very special. I'm sure its sensitivity is crap for speakers and its resonant frequency is very high for a driver of its size. You can't use it below 2kHz. Tak measured the HE-6 driver at 50cm distance and I think that also seemed pretty flat (like many other good headphone drivers). From a pure material coloration and distortion performance point of view I'd be interested in using the HD800 drivers as tweeters, if just for a comparison against other exotic tweeters. Anyway, enough rambling. I thought this would be interesting.