Why is headphone impedance spec taken at 1KHz?

I don't think there is a good reason.

 

Lots of FR graphs are centered at 1khz too, to be centered the human voice but that can vary quite a bit between genders, languages, and cultures.

It's probably some old convention.

I agree that it doesn't make much sense - you're better off looking at the curve on a graph.

And I sure wish more amp manufacturers would give us an output impedance curve.

I think it's just so that there's some sort of standard across multiple manufacturers.  Some number that you can directly compare given two datasheets/specsheets to look at.  I do agree, however, that it's not very useful unless you get to see the whole curve.

The keyword is nominal impedance.

 

Also, manufacturers like to play with the numbers and round them to their liking..

Edited by xnor - 6/29/11 at 4:49am

Aren't we the most sensitive to 1khz?

The loudness contours say 3khz.

Since you quoted me: Nominal impedance has nothing to do with sensitivity.

 

I think he meant the sensitivity of the human ear, not the headphone.

Doesn't matter, does it?

Well since FR can vary a lot combining impedance at the ear's most sensitive frequency with the transducer's sensitivity would give you a better estimate of perceived loudness and power requirements.  At least that's what I think he was getting at.

I see. Since you only get a single impedance number you cannot tell how the FR will vary over frequency, but yeah you could approximate power requirements for example.

 

I was saying it doesn't matter because nominal impedance is an estimated average of the speakers' complex impedance and is not really related to sensitivity pre se.

Edited by xnor - 7/1/11 at 2:08pm

Quote:

I totally forgot about speakers.  I was just thinking of the usual less complicated impedance curve that dynamic headphones have.

cause at 1khz is usually where the ''nominal'' impedance curve is at. they do that for speakers as well. they only measure at 1khz nowadays and put that down as the ''nominal''. some manufactures still do it the old fashion way, but lot just do it to make sells usually.

same can be said about amps as well. they're all measured@1khz only. that's why the wattage they list is completely bloated and inaccurate. they do not measure amps power@20hz-20khz per watt anymore. it takes time and money and to lot of companies ''time'' is money. that's why the only amps that are made nowadays like what they were use to back then cost 1000's. parts are expensive nowadays and manufacturing these fine and proper products takes lots of time and money to be properly measured and tested.

headphones are little different tho since it all depends on the strength of the magnet and how many wraps the voice coil gets to give the headphone it's ''impedance''. since the driver is small, headphones usually don't have the deep dips and high spikes on the impedance curve like speakers. that's another reason why damping factor is not much important to a headphone compared to speakers cause the impedance curve is very minimum.
Edited by RexAeterna - 7/8/11 at 8:19pm

Well, I wouldn't put it like that. Sure, you can say that for headphones it is less important but certainly not unimportant. I'd argue that most differences people hear between amps and portable devices with headphones is due to the interaction between output impedance (the higher it is the lower the damping factor) and headphone impedance. The differences can be as big as a couple of decibels.