Also, most subs have one or more impedance peaks in the 25-50 Hz range due to resonances, as well as climbing impedance with frequency due to voice coil inductance. In the cases I've actually measured or modeled it was more a case of impedance sometimes dropping to 7 ohms or so more than hovering around 8 ohms and dipping lower, if that makes sense. Taken as a broad band average from say 80 Hz down my current set of subs are something more like average of 13 ohms, with a ~7.1 ohm minimum.

[Warning: Some English was used to form the above]

Anyway, Euro, get well.