The ZERO 4X
The scope picture show frequency along the horizontal axis (log scale from 20 to 40KHz), and impedance along the vertical axis ( 2 ohms/ major line). Zero ohms is the bottom line, moving up there is 2 ohms on the next line, 4 ohms on the next line, etc. The lower trace is of an actual 4 ohm speaker. Notice that it exactly crosses 4 ohms at the center line (1KHz). The above line shows the impedance of the same speaker after its impedance has been multiplied by four (4x) with the ZERO autoformer. Notice that it now crosses 16 ohms at 1KHz.