How to Wire Your Subwoofers

Before I get into how subwoofers are connected to an amplifier, I want to take a moment to cover how a subwoofer works. The voice coil attaches to a sub-woofer’s cone at the tapered end. Alternating current (AC), which is the electrical analog or representation of music produced by the head unit, flows from an amplifier’s outputs through speaker wire to the sub’s terminals, which are in turn attached to the voice coil.

As current from the amp flows through the voice coil, the electrical charge causes the voice coil to react to the magnetic field of the subwoofer’s fixed magnet. Positive current makes the sub’s cone move forward or outward, whereas negative current makes the cone move back or inward. The movement of the cone compresses and decompresses the air in the listening space, producing pressure waves we perceive as sound. Depending on the speed at which it moves, the cone produces sounds at various frequencies. The frequency or number of times a cone moves per second is measured in Hertz (Hz).

As 1 cover the intricacies of subwoofer wiring, the important thing to keep in mind is the impedance or load that the amplifier ultimately sees. In a sense, the amp doesn’t really care how many subwoofers are sucking power from it, as long as it still gets the impedance it was designed to drive. The different wiring schemes are simply a way to load an amplifier so that it works at its maximum potential and reproduces an audio signal accurately and reliably.

The way to wire a single subwoofer to an amplifier is to connect the positive lead or wire from the amplifier to the positive terminal of the subwoofer, and the negative lead to the negative terminal (see Figure 16-10). If it’s a 4-ohm subwoofer, the amplifier sees a 4-ohm load. Using the previous example of a 120-watt stereo amplifier (60 watts x 2), if the two channels are bridged to mono, the amp sends about 150 watts to the subwoofer.

If you want to hook up more than one single voice coil (SVC) subwoofer to this same amplifier, you have a couple of driver-to-driver or subwoofer-to subwoofer wiring options, known as series and parallel, which I discuss in the next couple of sections. 

How to Wire Your Subwoofers

Series Wiring

With series wiring, the positive lead from the amplifier is connected to the positive terminal on one of the two subwoofers and the negative lead to the negative terminal of the other subwoofer, and then another wire runs between the remaining positive and negative terminals to complete the circuit. This causes the impedance to double. If you are using two 4-ohm subs, the amp sees an 8-ohm load. When possible, you should avoid series wiring between different subwoofers because it can cause non-linear behavior (for example, distortion) in certain cases.

Parallel Wiring

With parallel wiring of two subwoofers to a single amplifier, the positive lead of the amplifier is connected to each of the positive terminals of the subwoofers, and the negative lead is attached to each negative terminal of the subwoofers (see Figure 16-11). This causes the impedance to be halved. If you are using two 4-ohm subwoofers, the amplifier sees a 2-ohm load. 

Figure 16-11:

Parallel wiring of two subwoofers.

Because subwoofers come in 8-, 4- and even 2-ohm versions, by matching the impedance of the subwoofers and then wiring them in either series or parallel to raise or lower the impedance, a subwoofer system can be configured to make the amplifier perform at its optimum impedance.

In the series wiring example in the previous section, if you replaced the 4-ohm subs with 2-ohm subs, you’d end up with a 4-ohm load, which would produce more power. In the parallel wiring example, if you replaced the 4-ohm subs with 8ohm subs, you’d also end up with a 4-ohm load.

Dual Voice coil subwoofers

Dual voice coil (DVC) subwoofers offer even more flexibility. A DVC subwoofer has two separate voice coils that can be connected independently. With multiple subwoofers, DVC subs allow for not only series and parallel wiring, but a combination of the two called series/parallel wiring.

When a single DVC sub is wired to an amplifier in series, with the positive lead of the amplifier connected to the positive terminal of the subwoofer, and the negative lead of the amplifier connected to the negative terminal, and with a separate wire connecting the remaining two positive and negative terminals (see Figure 16-12), the impedance is doubled. For example, a 4-ohm DVC sub presents an 8-ohm load to the amplifier when the voice coils are wired in series. 

With parallel wiring of a DVC subwoofer, meaning that the positive lead of the amplifier is connected to both of the positive terminals of the subwoofer and the negative leads are connected to both of the negative terminals (see Figure 16-13), the impedance is half that of each individual coil. For instance, a dual 4-ohm subwoofer presents a 2-ohm load to the amplifier when the voice coils are wired in parallel. 

If you want to end up with a 4-ohm load at the amplifier, you can wire the two DVC subs in a series/parallel configuration. The positive lead of the amplifier is connected to two of the four positive terminals of the DVC subwoofers, and the negative lead of the amplifier is connected to two of the negative terminals of the subs, and the remaining pairs of the positive and negative terminals are wired together (see Figure 16-14). With series/parallel wiring with a pair of 4-ohm DVC subs, the impedance remains the same and the same dual 4-ohm subwoofers present a 4-ohm load to the amplifier.

Why All this Wiring?

Although this may seem like one big conspiracy to sell more speaker wire, the various connection schemes of DVC subs allows for flexibility when wiring subs to an amplifier. As mentioned previously, an amplifier doesn’t care how many subs it’s powering, as long as it sees the impedance that it needs to operate at its best. So the myriad connection schemes allow adding more subwoofers to get more bass without adding more amplifiers to power them.

An 8-ohm SVC subwoofer and a DVC 4-ohm sub look the same to the amp, for example. The advantage of the DVC 4-ohm sub is that it can be configured as an 8-ohm sub (with its two coils wired in series) or as a 2-ohm sub (with the two coils wired in parallel), whereas the 8-ohm SVC sub is capable of only one impedance.

If you’re using an amplifier that’s designed to run at higher impedances, either the 4-ohm DVC or the 8-ohm SVC sub should work fine. But if your amplifier is designed to produce optimum power at lower impedances, using the DVC 4-ohm sub and connecting the voice coils in parallel to yield a 2-ohm impedance is the way to go. 

With a pair of the DVC 4-ohm subs, you can wire the voice coils of each driver in series and the subs in parallel and get a final 4-ohm impedance. Or you could wire the voice coils of each driver in parallel and the drivers in parallel for a final 1-ohm impedance. With two SVC 8-ohm drivers, you can only achieve a 4-ohm final impedance, because all driver-to-driver wiring should be done in parallel. (Remember when I mentioned earlier that series wiring between different subwoofers should be avoided because it can cause distortion in certain cases?)