When testing for DC Resistance from a loudspeaker using a Digital Multimeter the value will typically be less than the rated Impedance, a number equal to half of the rated Impedance is not unusual. 2, 8-Ohm speakers in parallel would have an impedance of 4-Ohms, but could provide a DC resistance of approx. 2 Ohms). This is normal. Impedance is calculated based on the reactance of a load as it varies with AC signal frequency. The rated Ohm value for a speaker (8 Ohm, 6 Ohm, etc.) is the average Impedance the speaker will provide to the Amp when operated as a loudspeaker.