When you see a speaker rated at 8-ohms, it’s a nominal figure. Many speakers will dip below 8-ohms at certain frequencies, and could even dip below 4-ohms at some frequencies. I actually like “broadband” (I’m sure there’s a better term) impedance ratings like Magnat uses (4-8 ohms) – gives you a better idea of what the actual load is. Hopefully it means that the speaker actually and only ranges between 4-8 ohms.
Regards,
Wayne A. Pflughaupt