Subwoofers are a vital part of any good car audio system. They add the punchy bass that regular speakers cannot. When you are in the market for a new subwoofer you will commonly come across a term called impedance or see that a subwoofer is either 2 or 4 ohms (Ω).
First, it’s helpful to understand what impedance (also often referred to as resistance) really is. Impedance is a measure of the opposition to the flow of electric current by an electric circuit. Impedance is measured in ohms.
Subwoofers receive an audio signal in the form of an electric current from the amplifier. They have a particular level of resistance to an audio signal. Most subwoofers you’ll see have a resistance rating of 2 ohms or 4 ohms. Although most amplifiers are stable down to 2 ohms, it would help to know which impedance would produce the best quality and the loudest sound.
A 2-ohm impedance is on the lower side, meaning that it doesn’t have a lot of resistance in its circuit. Therefore, an amplifier is able to feed it more power without much resistance. Therefore, the subwoofer will be louder since there’s less resistance. On the other hand, it uses more power and this causes lower sound quality.
A 4-ohm subwoofer has a higher resistance. Therefore, it will consume less power and the bass will be less loud when used on the same amplifier. An easy way to combat this is simply getting an amplifier that is perfectly matched with your subwoofer. For example, if you have a 4-ohm subwoofer that can handle 500W RMS, then you should get an amplifier with a subwoofer channel (like a monoblock or a 5-channel) that outputs 500W @ 4-ohms. One big bonus of running a subwoofer at 4-ohms is that it produces a more compact sound with higher sound quality.
What about dual voice coils?
Throughout this article, we have mainly been talking about subwoofers with a single voice coil; However, we offer many subwoofers that actually have dual voice coils. You can have a sub with two voice coils where each one has a resistance of 2 ohms or 4 ohms. Dual voice coils just give you the ability to wire your subwoofer at one impedance or another. For instance, if you have a subwoofer with a dual voice coil where each coil has a resistance of 4 ohms, you can choose to wire it to have a higher overall resistance of 8-ohms or wire it to have a lower resistance of just 2-ohms. The same goes for a dual 2-ohm subwoofer; they can be wired at either 4-ohms or 1-ohm.
Which Impedance is better?
This answer, like most things in car audio, comes down to your preference. Are you someone looking for clean, clear bass? Then 4-ohms might be the better option for you. On the other hand, if you want to get the most power possible out of your amplifier and you are looking to really rattle the windows, wiring your subwoofer at a lower resistance would achieve just that. Most guys that compete in SPL (sound pressure level) competitions, that are just going for the loudest system possible, will usually wire their systems to the lowest impedance their amplifiers can possibly handle.
Above everything else, as I mentioned before, make sure to match your amplifier correctly to your subwoofer. We even have an in-depth article that talks all about this. This will allow you to get the most out of both components at whatever impedance you decide upon.