The 1 ohm resistor should be a reasonably precise 5W or better type.  The other resistors can be 1/2w or 1/8 watt 1% types.  The diodes are for protection.

When using this in PRAXIS, make sure to select "Current Sense " for the impedance measurement types, and set the probe resistors properly (there is a menu for that in the Levels Form, under "Setup->General").   You can also measure frequency response of loudspeakers when they are connected via this network, as the Probe2 is properly connected across the speaker terminals.
 
(The probes of PRAXIS aren't used with this, of course, the cables connect direct from the network below to the Audpod).