Subwoofers are a vital part of a car audio system. They add a deep bass where regular speakers cannot. When you are in the market for a new subwoofer you will come across a term called impedance that varies by type. The most common impedance is 2 or 4 ohms Ω.
It’s helpful to understand impedance (also referred to as resistance) before falling in love with a new unit. Impedance is the measure of opposition to the flow of electric current by an electric circuit – measured in ohms.
Subwoofers receive an audio signal as an electric current from the amplifier. Subs are built to have a set level of resistance to an audio signal so they don’t blow. Although most amplifiers are stable down to 2 ohms, it helps to know which impedance would produce the best quality and loudest sound.
An impedance of 2 ohm is on the low end of the spectrum, so it doesn’t offer a lot of circuit resistance. As long as an amplifier is designed to handle at least two ohms, it can feed the subwoofer more power for louder sound. The bigger output can lead to sound distortion.
A 4-ohm subwoofer has a higher resistance. It will consume less power and the bass won’t be as loud when hooked up to the same amplifier. An easy way to combat this is paring it with a better matched amp.
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 amp) 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.
The impedance of a subwoofer is set if it’s been constructed with a single voice coil. This isn’t so with a subwoofer that comes with two voice coils. Each one can have an individual resistance of 2 or 4 ohms that can be wired to one another in series or parallel to have a different total impedance.
If you have a subwoofer with a dual voice coil where each coil has a resistance of 4 ohms, it can be wired in series – wiring the negative and positive terminals of one sub to the neg and positive to the other. The final positive and negative wires are hooked up to the amplifiers output terminals. This gives you a total of 8 ohm, increasing the subwoofers’ final resistance.
To wire in parallel – the negative terminal from the first subwoofer is connected to the positive terminal of the second. The positive wire from the first sub and the negative wire from the second is then connected to the amplifier creating 2 ohms of resistance.
Which Impedance is better?
As with most things, purchasing or wiring subwoofers at different impedances comes down to preference, time and budget.
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.
Above everything else, accurately match your amplifier correctly to your subwoofer. We even have a post that talks all about this. This will allow you to get the most out of both components at whatever impedance you decide.