Increasing resistance on speakers
simulate this circuit &ndash; Schematic created using CircuitLab

Figure 1. Series connection of resistor.

Since you are increasing resistance in a series circuit the amplifier won't know or care where in the circuit the resistance is. Convention would be to put it in the red or '+' wire.







simulate this circuit

Figure 2. Simplified equivalent circuit.

The problem is that your speaker isn't just a resistor. It is largely an inductive load and since it has mechanical resonance (favourite frequencies to vibrate at) the situation becomes more complex. A good amplifier will have a strong drive to force the speaker to the correct position at any instant and overcome the inductance. Low resistance speaker cables are part of this equation. Adding your 2 Ω series resistance will affect how well the amplifier is able to control the speaker and some loss of fidelity will result.

Try it and see if you notice. The resistors will need to be rated to handle the power. Start with ones rated for at least 1/4 of the nominal amplifier output power rating.