There was a suggestion about possibly measuring the impedance of the M80s. Impedance varies with frequency and is fairly complex to measure, so it's better to rely on the measurements made by a competent lab, if available. In this case the NRC is certainly highly competent and has done the measurements, which have been shown here. If a particular M80 was somehow not representative of the published impedance curve and was in fact far lower, it should be noted that in that case the DC resistance of that driver's voice coil would measure far less than the typical 3/4ths of the nominal value(e.g., the DC resistance of a driver nominally rated at 4 ohms might typically measure 3 ohms or a bit more). The actual impedance to AC audio signals would be the DC resistance plus some additional impedance caused by reactance at various frequencies. So, if the DC resistance measured across the terminals is say at least 3 ohms, then the impedance at various frequencies will always be higher than that, and if the concern is the minimum impedance, the question has been answered.
