To design and build loudspeakers the most important thing is a way to test impedance. For that purpose I use something called the "Wallin Jig" named for Eric Wallin who designed the first jig. This is really not much more than a resistor in series - but by adding a bunch of switchable options, all possible Speaker Workshop impedance test and calibration capabilities can be done over and over without building anything further.

Go to:

• Eric Wallin's Speaker Workshop Jig Information

to see Eric's writeup of the jig. I use a slightly modified form of the jig. My jig and schematic are:

Click the jig (or schematic) for a larger view.

I use good banana jacks for the Z testing so as to minimize the serial resistance when testing. Clamping a component down in the jacks reduces impedance to below .1 ohms, which is great, although I often use banana jacks and clip leads to do the actual testing when .1 ohms is more than needed. Large clip leads run right around 0.1 ohms series resistance which is fine for most components, and quick and easy. The input can be either RCA (from the sound card) or banana jacks (from an amplifier). Similarly I have two reference resistors in circuit (soldered for low impedance connections). The switch labeled Ref is a three way toggle which is either shorting, or open, or uses one of the two reference resistors across the Z? spots. I've measured those two resistors extremely accurately and they are used to calibrate the jig with Speaker Workshop.