[bhanja_trinanjan]

Hi,
Could someone explain how impedance affects the drivability of a headphone?

We often say that loudspeakers with low impedance require more powerful amps than ones with higher impedance.

Why is it the opposite way around for headphones?

Say, a PX100 with an impedance of 32Ω will be easier to drive than a 300Ω HD800. Why? Please explain.

 

[logwed]

Quote:

Originally Posted by bhanja_trinanjan /img/forum/go_quote.gif Hi, Could someone explain how impedance affects the drivability of a headphone? We often say that loudspeakers with low impedance require more powerful amps than ones with higher impedance. Why is it the opposite way around for headphones? Say, a PX100 with an impedance of 32Ω will be easier to drive than a 300Ω HD800. Why? Please explain.

Basic Current/Resistance. Higher resistance draws more current to keep voltage constant across the headphone. I don't know how the statistics are explained with loudspeakers.

Yes, the PX100 will be easier to drive than the HD800. Also, sensitivity impacts the ease of driving.

 

[leeperry]

it's not. higher impedance phones are easier to drive, but they need more current...or something like that ^^

and sensitivity also matters, the worst to drive is when you have a very low impedance and a very high sensitivity(like the cd3k > 32Ω/104 dB)

if you don't use a killer amp, the cd3k will sound overly bright...

 

[bhanja_trinanjan]

Quote:

Originally Posted by logwed /img/forum/go_quote.gif Basic Current/Resistance. Higher resistance draws more current to keep voltage constant across the headphone. I don't know how the statistics are explained with loudspeakers. Yes, the PX100 will be easier to drive than the HD800. Also, sensitivity impacts the ease of driving.

But Higher Resistance = Lower impedance... So lower impedance cans should be harder to drive?

Then PX100 at 32 ohms impedance should be harder to drive?
But it isn't

 

[dan1son]

Lower impedance means they need lower voltages. Higher impedance means they need higher voltages... to keep the same output. Impedance alone doesn't really explain how easy or hard they are to drive, that's what the "sensitivity" rating is for.

Lower impedance phones will appear louder with the volume POT lower, but that doesn't necessarily mean the output current is lower as well. I guess my point is the knob doesn't turn up or down the current output, just the voltage output.

 

[Uncle Erik]

Yes, lower impedance headphones behave like low impedance speakers.

There are a few things that cause the confusion over impedance.

For one, speakers are more or less standardized at 8 Ohms, with a few at 4 Ohms and the occasional oddball that's higher. But since the vast majority are 8 Ohms, you don't have the problems with impedance matching the way you do with headphones. That also touches on manufacturers of power amps - build your amps for an 8 Ohm output impedance and they'll work with almost everything.

Headphones are different. There used to be an standard for 120 Ohms impedance, but as you can see, almost every manufacturer uses a different impedance. That makes it difficult for an amp manufacturer to design an amp that will drive a variety of headphones.

The only good solution is to use transformers with multiple taps for each popular value. Only Sowter makes those (though you can order customs) and they're not cheap - it cost me $500 to have a pair shipped over.

Anyhow, the question you should be asking is, "how hard will a headphone be to drive given the output impedance of my amplifier?" You cannot make a generalization about headphone impedance unless you also know the output impedance of the amp you're going to power them with.

 

[Donald North]

Quote:

Originally Posted by bhanja_trinanjan /img/forum/go_quote.gif Hi, Could someone explain how impedance affects the drivability of a headphone? We often say that loudspeakers with low impedance require more powerful amps than ones with higher impedance. Why is it the opposite way around for headphones? Say, a PX100 with an impedance of 32Ω will be easier to drive than a 300Ω HD800. Why? Please explain.

To generate a specific sound pressure level (SPL) requires an amount of input power based on the efficiency of the headphone.

Power is voltage multiplied by current. For a specific power, a low impedance headphone will need less voltage but more current than a high impedance headphone. Same applies with loudspeakers. If you have 4 ohm speakers, you need an amplifier that is rated to power 4 ohm speakers without problems like current limiting.

Portable electronics are frequently limited by their available voltage due to type of battery being used. With limited voltage and the desire to deliver higher power into headphones, portable headphones are usually the low impedance type. Using the same portable device to power a high impedance headphone, the portable will probably run out of available voltage swing before reaching satisfactory SPL. Perfect example: An iPod with 600 ohm AKG K240DFs is not a good combination

 

[HONEYBOY]

Guys this question has popped up so many times. Here's a link , where I think Cool Torpedo did a great job explaining the relationship between Impedance, Drivability and how sensitivity comes in to play:
http://www.head-fi.org/forums/f4/exp...ce-all-350423/