Option 1: Use a 1 ohm stable amplifier
The most straightforward way to reduce the ohms from 4 ohms to 2 ohms is to use a 1 ohm stable amplifier. This type of amplifier is designed to handle the lower impedance load and will provide your subwoofers with the power they need to perform at their best.
Option 2: Wire your subwoofers in parallel
Another way to reduce the ohms from 4 ohms to 2 ohms is to wire your subwoofers in parallel. This involves connecting the positive terminals of both subwoofers to the positive terminal of the amplifier, and the negative terminals of both subwoofers to the negative terminal of the amplifier. This will effectively halve the impedance of the load, resulting in a 2 ohm load.
Option 3: Use a series-parallel speaker wiring configuration
A series-parallel speaker wiring configuration can also be used to reduce the ohms from 4 ohms to 2 ohms. This involves wiring two subwoofers in series (positive terminal of one subwoofer connected to the negative terminal of the other subwoofer) and then connecting the remaining positive and negative terminals of the two subwoofers to the positive and negative terminals of the amplifier. This will result in a 2 ohm load.
It is important to note that when reducing the ohms of a load, you are also increasing the current draw. This means that you will need to make sure that your amplifier is capable of handling the increased current draw. If you are not sure whether or not your amplifier can handle a 2 ohm load, it is best to consult with a qualified car audio technician.