The Ohm load doesn't refer to the speakers as it does the amp. You actually change the load on the amp by wiring the speakers differently. Which in turn makes the amp put out more or less power. The lower the ohm the more power put out by the amp. Also the hotter it gets. The only time you don't want a lower ohm on your amp is if it can't handle it. If your speakers are 4 ohm when you wire them in parallel it drops the ohms to 2. When you wire them in series it raises the load to 8. So if you wire 2 speakers in parallel it drops to 2 ohms. Then wire the third speaker in series it raises it double of the first two which would be 4 ohms, but there's only one in series so that would actually make the impedance 2 ohms.
Now that being said. I'm not 100% sure about that, and i only had a minute to type before my wife kills me
Here's a couple diagrams.
This is what your configuration would look like except the speaker on the bottom would be 4 ohm.