Speaker Workshop is really using a simple
voltage divider to measure resistance. As a result,
when you use something like the Wallin jig with a fixed
voltage divider resistor, your results are extremely
accurate within a limited range and accuracy drops off
outside that range. The program uses the reference resistors
- in this case 10 and 5 ohms - to figure out the accurate
What we see with the above results is
excellent precision from 2-15 ohms with dropoff to about
1% error at 33 ohms. This is virtually perfect for speaker
testing and building - hence the value of a jig with
soldered in resistances and consistent results.
If you want to test larger resistors I
recommend a bigger dropping resistor.
Finally, I was surprised and impressed
with the accuracy shown above - it may have been a fluke
but the test was done without any attempt to fudge the
figures. I was extremely careful with the calibration
and getting results quickly so resistors didn't drift,
Precision is a function of the
linearity of the ADC used on the sound card and the
linearity and noise of the input buffering circuitry
and the noise of the output amplification.