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How to Connect Two Subwoofers to a One Channel Amp

Whether you’re a serious basshead, audiophile, car audio fanatic, or someone who likes to rock out — really loud and hard, a car audio system with multiple subs not only looks badass, but it can significantly improve the bass in your vehicle. However, a multi-sub setup is only practical and functional as long as you wire it correctly.

A bad wiring job can wreak havoc in your stereo system and land you with a blown subwoofer, a burnt up amp, or in some cases even catch your car on fire.

In this guide, we’ll walk you through how to connect two subwoofers to a one channel amplifier. This might seem puzzling at first, but it’s actually doable and not that difficult at all. I mean, this really isn’t that much different from wiring one single subwoofer to an amplifier.

So, without any further ado, let’s get started.

Before you get started

Wiring subwoofers can be a tricky business especially if you’re a relative greenhorn when it comes to car audio, or if you haven’t done the research to fully grasp the concept.

There has always been a lot of confusion and misunderstanding specifically surrounding watts, amps and impedance, which all relate directly to ohms law and hence, subwoofer wiring. For this reason, understanding speaker impedance and how it works (which will be covered below) is really useful when connecting multiple subwoofers to an amplifier.

Speaking of which, there are many different ways to wire subwoofers and amplifiers together (more on this down below). The ideal setup is when the power capabilities and impedance of your subs are perfectly matched to your amplifier.

Essentially, there are two important key elements to every subwoofer that determine how you will wire it and the impedance load you’ll get; the latter must match your amplifier’s impedance capabilities. The first element you must know is how many voice coils your subwoofers have? The second thing you must know as well is if your subwoofers have single or dual voice coil?

Using these information, you’ll be able to figure out the optimal load and maximum power output for your amplifier.

Car amplifiers have a maximum load that is measured in ohms. It’s critically important to know what that maximum load is and to not exceed it by any means.

Subwoofer Wiring Options

First and foremost, it must be noted that the overall impedance load of your subs changes depending on how the subs and their voice coils are wired together — in parallel or in series, or in a combination of both.

Series Wiring

Series wiring refers to connecting the positive terminal of the amplifier to the positive of the first subwoofer, and the negative of the first subwoofer to the positive of the second subwoofer, and so on. The negative of the last subwoofer is wired back to the negative of the amplifier forming one large loop.

To figure out the total impedance of multiple subs or voice coils wired in series, you add the impedances of the voice coils, so wiring two 4 ohm voice coil subs would result in 8 ohms for the system total as presented to the amplifier.

Total Impedance = Sub I1 + Sub I2 + Sub I3 + …

Parallel Wiring

In parallel wiring, the terminals of each subwoofer are connected to the same things — plus to plus, and minus to minus forming two loops.

While wiring multiple subs in series increases the overall resistance of the circuit, wiring them in parallel decreases the overall resistance of the circuit.

With subwoofers rated at equal impedances. The overall impedance load of multiple subs wired in parallel is equal to the impedance of one sub voice coil divided by the number of subs. So, if you have two 4 ohms subs wired in parallel, their overall impedance load is 2 ohms (4 ohms divided by 2 subs).

Total Impedance = Sub Impedance/# of Subs

Since parallel wiring lowers impedance, it’s highly recommended that you always double check to ensure your totals do not run into unsafe levels especially when bridging an amp to increase the rated power available.

How to Hook Up 2 Subs to a 1 Channel Amp

Now that we’ve explained the different ways to wire subs, here’s how you can connect two subs to a mono channel amplifier.

First of all, start by running a wire from the positive terminal on the amp to the positive terminal on the first subwoofer. If you wish to wire your subwoofers in series, run another wire from the negative terminal of the first subwoofer to the positive terminal of the second subwoofer.

If you wish to wire your subwoofers in parallel, you will need to run two wires between the two subs. The first wire will connect the two positive terminals, and the second will connect the two negative terminals.

Finally, whether your subs are wired in series or in parallel, you need to complete the circuit by connecting the wire from either the first or the second sub’s negative terminal to the negative terminal on the amp.

The main downside to wiring your subs in series is that if one of your subs goes out the others will as well due to the way the subs are connected. In a parallel circuit, only the failed subwoofer will stop producing sound.

What Is Speaker Impedance & Why Does It Matter?

If you already understand what impedance is and why it matters, then you don’t need to further read this article unless you are just curious.

Essentially, speaker impedance refers to the load a speaker places on an amplifier. It’s measured in ohms, and uses the Omega symbol (Ω) for shorthand.

Technically speaking, impedance is the “resistance” a speaker offers to the current supplied by an amplifier. However, unlike resistance which is a constant value, impedance is constantly changing depending on frequency. So, rather than stating the impedance for every frequency, speaker manufacturers state the “nominal” impedance, which is a rough average of the lowest values of the speaker impedance.

Most car speakers are rated by the manufacturers as nominally 2Ω, 4Ω, or 8Ω.

The term “impedance” comes from the Latin word “impedire” and it means “to impede” or “to restrict” the current, so the lower the impedance, the more current can flow. A greater current requires the amp to produce more power. In other words, the lower the impedance, the higher the load on the amp (and the harder it has to work).

All of this can be summarized by:

  • Low impedance → more current → greater load → increased power
  • High impedance → less current → smaller load → decreased power

Looking at the summary above, it appears that the lower the speaker(s) impedance presented to the amplifier, the greater the power the amp delivers through that speaker(s). This is true – up to a point. It is true up to the point where the amplifier is no longer capable of keeping up with the increased demand for current and power. At this point, either the amp fuse will blow, or the protection circuit in the amp engages and turn the amp off to prevent serious damage. For this reason, it’s highly recommended to avoid running an amplifier with a load impedance of less than the stated minimum.

Why Do You Need to Know About Speaker Impedance?

Well, for one simple reason, and that is to make sure the impedance of any speaker connected to an amp is within the capabilities of the latter. This is a real concern when you hooking up multiple speakers to one amplifier. For example, four 4Ω speakers wired in parallel across an amp gives a total load impedance of only 1Ω – which could be way too low unless your amplifier is stable down to 1 ohm load.

Alex Brown

Hey There, my name is Alex Brown, I'm an LA-based sound engineer with over 10 years experience installing, troubleshooting, and repairing commercial, automotive, and household sound equipment. I've installed highly competitive car audio systems, and everything from navigation systems to full car stereo systems, remote starters, alarms and beyond. I enjoy creating solutions and simplifying everyday needs. I also love helping people get great sounding gear, thereby, saving the world from bad sound one customer at a time.

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