how is the impedance of a headphone calculated?

[terrymx]

i'm wondering what determine the "ohm" of a headphone. is it both the cable and driver? if the cable is the factor, than is it base on the material that made it up? can you change the "ohm" by replacing the cable for a headphone?

 

[pedxing]

You can easily change the impedance with an adapter that contains a resistor. People with certain Beyer headphones use a 120 Ohm adapter. Ety ER-4p people sometime buy a special adapter that will increase the overall impedance, making it sound like an Ety ER-4s.

Everything that has resistance will contribute to the impedance of the headphone, including cable and the driver. Certain headphones may have varying impedance that is depedent on the frequency of the signal. Headroom has impedance charts of many headphones. Many headphones with varying impedance usually have their impedance peak around the bass region.

 

[saint.panda]

Please bear with my bad English explanation ("x" is times and "/" is divided by):
Resistance = angular frequency x inductivity
Inductivity (in a spool) = (some sort of constant) x number of convolutions (squared) x cross-section of the spool / spool's length

So I guess it really depends on the spool's properties inside the driver. Note that the impedance isn't constant anyway but some sort of average of a sine-function.
I might be mixing things up, just let me know if that's the case.

Edit: AFAIK impedance is just the resistance in an AC circuit.

 

[JaZZ]

The nominal impedance of a headphone is the average of the AC (alternating current) resistance -- approximately. The bass resonance as well as the voice coil's inductivity cause a peak in the bass and a rise towards highest frequencies. The cable usually has little influence; its AC resistance is somewhere near 1 ohm.

 

[D-EJ915]

Quote:

Originally Posted by JaZZ The nominal impedance of a headphone is the average of the AC (alternating current) resistance -- approximately. The bass resonance as well as the voice coil's inductivity cause a peak in the bass and a rise towards highest frequencies. The cable usually has little influence; its AC resistance is somewhere near 1 ohm.

That's weird because speaker drivers impedence is measured with DC resistance.

 

[JaZZ]

Quote:

Originally Posted by D-EJ915 That's weird because speaker drivers impedence is measured with DC resistance.

Actually it's exactly the same with speakers. If you measure the DC resistance of an 8-ohm speaker chassis it's somewhere around 6 ohm.

 

[Dusty Chalk]

Quote:

Originally Posted by D-EJ915 That's weird because speaker drivers impedence is measured with DC resistance.

They are? Every time I read a review that includes measurements, they usually plot the impedance as a function of frequency and point out dips at certain frequencies and explain them. Then they sort of average them. It would be better if they showed a range (lowest, highest, etc.). It would explain their ease of drivability.

 

[ServinginEcuador]

In almost all cases the cable is so negligible it is left out. Even a bad cable will add well under .5 ohms.

I calculate it as follows: Grados are 32 ohm, so are Sonys (except the R10 which is 40ohms), Senns are generally 300 ohms, and Beyerdynamics are 250 unless the name is different and ends with -80 or something.