[Zoltan99]

What's the point of high impedance headphones?  I see some models have two options (Low and High impedance).   So why would anybody go for the high?

 

[jcx]

OTL tube amps

 

[radioactive28]

Check this out: http://www.dolphinmusic.co.uk/article/321-headphones-impedance.html
 
Basically, not all head/earphones were made for low-powered portable devices. You'll find that many high-impedance headphones were originally made for monitoring purposes. Even small mixers can have watt-level headphone outputs, which can easily blow low-impedance loads.

 

[Ypoknons]

Dampening factor, there's still some debate about its importance in headphones IIRC but it would seem it'd be easier on home receivers hp outs and the like to control a higher impedance headphone, just a guess though (though that's definitely true for OTL tube amps).
 
(edit and expansion) - shigzeo notes that most receivers have 120ohm output. if that's accurate, then in addition to studio headphones, I imagine most HD650's, DT880 and the like are actually sold to people using receivers at home (their retail outlets tend to be hifi shops, the dedicated headamp scene is pretty new, really only took off in the early 2000's I think), so having something like 300ohm impedance would make it a safer bet that the receiver can control the headphone's drivers. But these are of course, laymen guesses, I'd be kind of happy if someone corrected me, actually hahaha

 

[DrSpiv]

One of the biggest things is induction: If you want to change the charge on a coil it takes a certain amount of time (called induction or induction rate). In a speaker you are constantly varying the voltage to cause it to vibrate. Voltage is an electromotive force, so the higher you have the faster you can make this change. Of course you can't just charge a speaker at a super high voltage and not expect it to be destroyed, so you have to do something to limit the total current being applied. Total work being done has to remain the same as if the force (voltage) was the same as with a low resistance system.
 
If you crank up the impedance, you can use a higher electromotive force, and therefore increase the rate of induction. This gives you a faster response time to the signal being provided. This is wasteful (energy use wise), which is why it's harder to drive higher impedance phones.
 
<-- did a lot of CNC equipment, and electric motors are just the same (a coil is a coil). You can get them to change phases faster by building a current limiting circuit (although in our case we could get the efficiency back by using some specialty chopper circuits to achieve specific levels at very high voltages (IE providing 70-90 volts to a motor rated for 5 volts so it could switch phases with close to maximum torque at high speeds). In cheaper systems they just stack some big resistors at the powering section and crank the voltage, but then the power requirements go up significantly.

 

[b0dhi]

 
Quote:

What's the point of high impedance headphones?  I see some models have two options (Low and High impedance).   So why would anybody go for the high?

Higher impedance models use a thinner, lighter voice coil. Ideally the voice coil should weigh nothing.

 

[jcx]

Quote:

 

Higher impedance models use a thinner, lighter voice coil. Ideally the voice coil should weigh nothing.

if the manufacturer wants they can use the same total weight of copper and with thinner or thicker wire (and a compensating more or fewer turns) give you different impedance - exactly equivalent to designing in an ideal transformer
 
if they go this route then the electro-acoustic response should be exactly the same - same sensitivity in dB re mW, same low frequency resonance and Q - it should sound the same except for the "built in" transformer ratio changing the I,V ratio required from the amp - of course any amplifier output impedance gives different damping ratio unless you can also switch the series output R