No, Alex; the voltages are divided in proportion to the relative magnitudes of the two resistances. In the example I gave above the speaker would take a relatively larger proportion of the voltage at 12 ohms(the resistor remaining fixed at 4 ohms)and following Ohm's Law, as usual, would be relatively louder at the 12 ohm frequency than at the 4 ohm frequency even if the output voltage from the amplifier was the same at the two frequencies and they should be equal in loudness.

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Enjoy the music, not the equipment.