jensigner
Well-known member
BTW how do you measure the earbud impedance?
For most common earbuds and phones which are mainly resistive at the standard test frequency of 1 kHz, it is pretty simple: Set up a simple voltage divider circuit (one for each channel if you want) with a single extra resistor Rs in series with the buds R_hs, drive the series circuit with a SMALL SIGNAL sine wave at 1 kHz, say ~ 50mV for buds, using a function generator and measure the output voltage compared to the input voltage and apply simple voltage-divider Kirchoff law. The series resistor value is not critical ... just pick a value in the general area of the headphone impedance for a more accurate calculation. I use a USB scope (Digilent Discovery) for this and just measure the peak voltages but you could also just use a DVM (since most DVMs have a reasonable response at 1 kHz). A scope lets you monitor the signal quality (to make sure you aren't clipping or causing other distortion) and also allows you to see any non-resistive components of the earbuds which shows as a phase-shift in the two scope signals V3 and V2. Note that the internal resistance (Rint) of the function generator doesn't enter into the calculation:
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