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.
John, ohms law is for an entire circuit. you have to use Kirchhoff's voltage/current law for components within a circuit.
KVL's are used to calculate the voltage seen at a component level from a voltage source. There is a voltage loss across each component in a series circuit and can be calculated by using a KVL...
http://en.wikipedia.org/wiki/Kirchhoff's_circuit_laws
However, at this point we are using DC equations.. AC gets much more complicated, I chose the KVL for the ease of conceptual understanding.
