I was surprised to learn that the expensive amp HDVD800 have an output impedance of 43 ohms.
Also there's an article that use a weird analogy with pendulums, suggesting that both overdamping and underdamping problems could exist for headphone. But I'm not sure the analogy is appropriate.
Now imagine a huge motor attached to the pendulum. In this case the motor is so big that it hardly feels the pendulum’s moment at all. The motor will be able to do what ever it wants regardless of whether it’s near the resonant frequency or not. The large available horsepower of the motor “damps” the pendulum’s natural moments.
An over-damped system (orange) will be slow to respond.
Its even possible that some headphones improve with a higher impedance. But if that's the case, a high-quality manufacturer would add resistors inside the earcups (and they would still test & specify with a low impedance amplifier).
Are you sure that's the effective output impedance? (I didn't see the output impedance or output voltage spec on Sennheiser's website.)
So you have hd800 (300 ohm) with the amp HDVD800 (43 ohm) which imply a damping factor of roughly 7.Then you have the beyer T1 (600 ohm) with the amp beyer A1 (100 ohm) which imply a damping factor of 6.I think this follows a commercial logic.
A HD800 on a HDVD800 would show a 0.5 dB deviation from ideal FR on a 43 ohm output. Probably audible, but minor in the grand scheme of things. I typically use a 1 dB criterion to determine whether a match is OK.
As far as overdamped cans go, I'd say 50 ohm HD555/595s are, most of them at least - i.e. the "bass-light" version. Not the worst move for home hifi cans, given their fairly extreme impedance swing (min/max ~50/250 ohms). They sounded somewhat anemic on low-impedances sources though.
Its really hard to hear even a 1 db difference.
Its really hard to hear even a 1 db difference. I doubt a fractional db change matters.