However, there are manufacturers that make 2-ohm dual voice coil and 8-ohm dual voice coil speakers. (You can even buy 3-ohm speakers.) With 2- and 4-ohm products, the results can be 1/2-, 2-, or 8-ohm or 2-, 16-, or 32-ohm options. If you were to swap your 4-ohm speakers with the 2-ohm versions, then you could hit the 2-ohm target, but again, without knowing which amplifier you have I can't tell you if it is optimized for a 2-ohm load.
Also, watch out for the term "1-ohm stable." This means that the amplifier will still play, even though the load is really close to a short circuit, without shutting off. It doesn't mean that it will produce more power or that it will even maintain the power you would get at 2 ohms. Today, if you're running at anything over 2 ohms, most amplifiers are stable. Running a bit below that limit won't kill your amplifier or speakers, but the life span of the gear would be shortened slightly. Going from a 50-year usable life to 45 years may not be a big deal to anyone.
Let's look at this from another angle: How much louder would the system play if you were able to get your speaker system to hit 2 ohms? If your amplifier won't produce any additional power at 2 ohms as opposed to 4 ohms, then the benefit is zero. Basic math would tell us that if you halve the load resistance, power would double based on the Watt's Law formula of P = E2 R (Power = Amplifier output voltage squared, divided by load resistance). A 20-volt amplifier into a 4-ohm load results in 100 watts, so the same 20-volt amplifier into a 2-ohm load should deliver 200 watts. Not so fast.
Another law gets first priority-the Law of Conservation of Energy says that energy cannot be created or destroyed, only changed from one form to another. If a 100-watt mono amplifier has a 15-amp fuse on the power lead, then to produce 200 watts would need closer to a 30-amp fuse, otherwise it's impossible. "Replace the fuse with a 30 amp," my students say. I say, "No way." That tends to let all the smoke out of the amplifier (check out "magic smoke" on Google). Overall, even when a larger fuse is inserted, the amplifier might produce an extra 20 percent more power. Before you jump at this as being an improvement like "20 percent better gas mileage," note that sound in logarithmic rather than linear in nature. It takes 3dB of change to produce a usable increase in volume, and to get 3dB requires a power change of double! Going from 100 watts to 120 watts gives us a benefit of less than 1dB-barely noticeable and probably not worth extra money to try and solve. It's also dangerous, since the fuse size was designed in for a reason. Oversizing a fuse simply removes the safety feature that keeps your amp from becoming a smoking memory in your trunk.
What you might notice is that whenever you drive an amplifier below its optimum load the distortion will begin to rise. In many cases it also won't be noticeable by ear, but the fact that the amplifier is distorting more than the normal amount means that the amplifier is probably working harder than it should.
There's a lot more to the topic than what I am able to cover in the column, so make it a point to learn more. It's great having a hobby that's fun to learn, and even better when it is your career!