[morto00x]

First post in Head-fi (been lurking for about a year). I've been wondering if a time-domain reflectometer (TDR) be used to measure the impedance of headphones. I know it is used to measure the characteristic impedance of cables, PCB traces and connectors.
 
I have no need to measure the impedance of headphones right now, but I'd like to know if that would count as a valid testing method (I'm an EE and I've been getting really interested in audio lately, mostly because of this forum).

 

[Speedskater]

What model TDR do you have sitting on the workbench that you are looking for fun things to test?

 

[morto00x]

The TDR I have at work is a HP54754A module for a HP54750A oscilloscope. It belongs to the lab, so access to it depends on availability.

 

[Speedskater]

I didn't find much info on the HP54754A,  but he little I saw was testing in the GHz range.  I think you need to find another test instrument or another project.

 

[mikeaj]

I've never used a TDR before, but is the resolution suitable?  If you're sending an impulse or pulse through the headphones and looking at what comes back, considering quantization... don't see how you're going to extract impedance in 20-20 kHz range easily from that.  You're mostly just going to see the effect of the impedance at frequencies way above audio from the inductance of the voice coil, right?  Or?  Urgh, I forgot all sorts of things about transmission lines.
 
I take it you don't want to do some "boring" test tone through headphones in series of resistor and probing for voltages?

 

[morto00x]

It was more of a curiosity since, as I mentioned before, I have access to the TDR. I'll try to test my headphones on next week just to see what happens.