Different impedance in headphones: how and why??

[sonicm]

So I was shopping for a pair of headphones, when in the reviews of a certain pair I read "There are variants to the 990 that come as low as 32 ohm and as high as 600 ohm". Now I know only this one company makes the same model in different impedance. But I've never considered impedance as a factor in sound quality before, and then two questions stuck me;
1. If this single model of headphones comes in different impedance values then what's (physically) different between them?
Why
2. And if there's something physically different between them, are there other differences in sound quality? And if so why would that be.
From what I looked I couldn't find anything. From what I've read some people reported that higher impedance sounded better, but I don't know why that would really be. I wonder if that's just because the amp is coloring the sound more or something? Regardless, I'd like to know how this works if anyone knows

 

[ProtegeManiac]

Depending on the amp, higher impedance can mean less distortion, particularly in keeping the output impedance of the amp much lower than the load impedance. It also tends to increase sensitivity in many cases, so that means it usually offsets the drop in output power. Basically that makes the headphone easier to drive for multiple reasons.

That said, in some cases if the amp's output drops far enough that even the higher sensitivity can't compensate, vs a lower impedance headphone where the amp can deliver a lot of power, THD increase and drop in sensitivity can also be negligible.

Ten years ago it would be very preferable to go with high impedance designs given the prevalence of high output impedance amps that also don't produce much clean power, but by now there are a lot of amps that aren't restricted in those areas. Even some USB-powered DAC-HPamps can produce 250mW at 32ohms (though it drops a lot more at high impedance loads unlike AC-powered amps) and have very low output impedance.

 

[kman1211]

So I was shopping for a pair of headphones, when in the reviews of a certain pair I read "There are variants to the 990 that come as low as 32 ohm and as high as 600 ohm". Now I know only this one company makes the same model in different impedance. But I've never considered impedance as a factor in sound quality before, and then two questions stuck me;
1. If this single model of headphones comes in different impedance values then what's (physically) different between them?
Why
2. And if there's something physically different between them, are there other differences in sound quality? And if so why would that be.
From what I looked I couldn't find anything. From what I've read some people reported that higher impedance sounded better, but I don't know why that would really be. I wonder if that's just because the amp is coloring the sound more or something? Regardless, I'd like to know how this works if anyone knows

There is actually a physical difference with the Beyers, it's more than just amplifier differences and how well they are driven by the amplifier with clean power. In regards to the low and high impedance Beyerdynamics, the physical difference is in the voice coil, the higher impedance versions actually have lighter voice coils, this means a lighter overall driver, which means a faster more responsive transducer. Because of this, with the Beyers, the 600 Ohm is actually technically the best of all the versions. Voice coil and magnet designs are vital to sound quality, what may seem like a small change can have audibly noticeable differences.

This is in regards to the Beyers, it may not be the case in other headphones, for example the Focal Elear and Clear use different materials in their voice coil and even though the Clear has a lower impedance it is technically superior to the Elear.