Originally Posted by ab initio
I am fully aware that some IEMs can do some pretty wonky things in terms of impedance and response to poor output impedance, etc... but admittedly, I never use IEMs and don't usually considering them when thinking about headphones, etc. As unfair as that may be.
I think it's a little ironic and quite funny that of all the headphones that might benefit the most from beefy cables, it's precisely the headphones that would most easily get ripped right out of your ears by a bigger, bulkier cable.
These are cables, and they cannot have that much impedance, but guess what, I found this article from Tyll's blog.
Here is an interesting exerpt from this article http://www.innerfidelity.com/content/headphone-cable-measurements-wrap
An Avenue for Exploration
I did manage to stumble into what seems to me as a particularly interesting avenue for further exploration and development. I had a discussion with Dr. Kevin Gilmore (who many of you know from his terrific work designing commercial and DIY electrostatic headphone amplifiers) in which he stated that the effectes of impedance matching with headphone cables could be of an order strong enough to influence the listening experience.
All cables have a characteristic impedance. For example, I use Canare 4E5C cable for my cable building needs. This cable has a 40 Ohm characteristic impedance. If I were to build a headphone cable for a Sennheiser HD 600, which has a 300 Ohm impedance, there would be a point at the headphones where the signal went from the 40 Ohm impedance in the cable to the 300 Ohm impedance of the driver. This impedance mismatch would cause a point of reflection for the signal. There is an instrument call a Time Domain Reflectometer that is able to send a signal down a cable and see the various points of reflection caused by impedance mismatches (and other things). The reflected signal from the impedance mismatch can, depending on the topology of the amplifier in use, have an effect on the signal from the amp. To properly impedance match the cable to the headphones in this example case, you would have to put a 40 Ohm resistor between the signal and ground at the headphone end of the cable. This would dramatically reduce the reflected signal.
A further twist on cable impedance matching is to impedance match the output of the amp to the cable. This works better for interconnects where the damping factor between the source and load isn't as important.
It seems to me this is a readily available avenue for further development by custom headphone cable makers.