Proper subwoofer wiring may seem like a small detail but it can make a big difference in how your system performs. Not knowing how much load you are applying to your amplifier could leave you with an underpowered subwoofer or an underloaded amp. Both of these scenarios can cause damage to your equipment.
First let’s talk about the ways an improperly loaded amplifier can damage your equipment, then we’ll discuss how to calculate your total load in different scenarios so that you can optimize your sound system.
Why You Should Not Underpower Your Subwoofers
I’ve discussed this already in my post on How to Choose the Right Amplifier for Your Subs but I’ll cover it again here.
Let’s say you have a dual 2-Ohm voice coil subwoofer rated for 1000 Watts RMS. Your amplifier can supply 1000 Watts RMS at 1-Ohm or 300 Watts RMS at 4-Ohms.
If you didn’t know any better you might end up wiring the voice coils in series leaving you with a total load of 4-Ohms. With the amplifier in this example you would only get 300 Watts RMS to your 1000 Watt RMS rated subwoofer.
The problem with underpowering your subwoofer, like in this scenario, is that you get what’s known as “clipping” of the audio signal. This is a source of distortion that not only ruins sound quality, it also damages the subwoofer.
Clipping happens when your amplifier is trying to drive the audio signal to the peaks and valleys of the sound wave but it runs out of power. Since it can’t drive the signal all the way, the peaks and valleys end up getting clipped. Check out the figure below to see what this looks like visually.
The clipped audio signal will cause your subwoofer’s voice coils to heat up. The voice coils will eventually fail when exposed to this excess heat over time.
Why You Should Not Underload Your Amplifier
If you take a piece of wire and touch one end to the positive terminal of your battery and the other end to the negative terminal of your battery you have created a short circuit (DO NOT DO THIS…SERIOUSLY!). Since there is virtually zero resistance between the terminals, the current in that wire will be nearly infinite causing heat and fire and generally bad things until something breaks that connection.
Resistance (measured in Ohms) in a circuit is what restricts the current to manageable levels. For all intents and purposes, you can think of the impedance (also measured in Ohms) of your subwoofer’s voice coils as resistance. The closer your overall impedance gets to zero, the closer you are to a short circuit and the more current runs through the amplifier’s output terminals.
In many of the examples that I give, I say that some hypothetical amplifier produces 1000 Watts RMS at 1-Ohm. The truth is that not all amplifiers are stable at a 1-Ohm load. This basically means that the internal circuitry is not built to handle the amount of current that would result from only applying just 1-Ohm of load to the output terminals.
In the example I gave earlier, if you wired the dual 2-Ohm voice coil subwoofer in parallel, the overall impedance of that sub would be 1-Ohm. And if you connect that 1-Ohm sub to an amp that is not 1-Ohm stable, you could cause serious damage and eventually fry the amp.
How to Calculate Total Load
Okay, so now that you know what you should avoid, let’s figure out how to calculate the total load so you can avoid those situations.
First we’ll get the boring math out of the way, and then I’ll give you some examples. In the formulas I give below, RT is the total calculated impedance and R# is the impedance of the individual voice coils.
There are two ways to wire voice coils together; series and parallel.
A series connection is made by daisy chaining the voice coils together. The negative of the first voice coil connects to the positive of the next and so on for as many voice coils as you have. The figure below shows how resistors are connected in series, and the same would apply for voice coils.
The total impedance of multiple voice coils wired in series is just the sum of the individual impedances. The formula looks like this:
A parallel connection is made by connecting the positive terminals of all voice coils together and the negative terminals of all voice coils together. The figure below shows how resistors are connected in parallel and again, the same would apply for voice coils.
There are a couple of different formulas you can use to determine the total impedance of multiple voice coils wired together in parallel.
The formula below is the general formula for calculating the total impedance of any number of parallel voice coils.
If you only have two voice coils, (this can be the two voice coils on a dual voice coil subwoofer or it can be two separate single voice coil subwoofers), you can use the simplified formula below.
Load Calculation Examples
Let’s take a look at a couple of examples.
Four Single 4-Ohm Voice Coil Subwoofers
There are technically two ways this subwoofer setup can be wired together, but only one is realistic. If these four subwoofers were to be wired together in series the total load would be 16-Ohms. This is much too high of a load and chances are the subwoofers will be underpowered.
If they are wired together in parallel, we can use the formula above to calculate the total load.
This subwoofer setup will work perfectly on a 1-Ohm stable, mono amplifier.
Four Dual 4-Ohm Voice Coil Subwoofers
Things can get a little complicated when you’re facing several dual voice coil subwoofers. You might be thinking you only have two options for wiring this setup; wire everything together in series or wire everything together in parallel.
The trouble with that approach is that you end up with either very large or very small total impedance.
Between the four subwoofers, there are a total of eight 4-Ohm voice coils. If these were all wired in series, the total load would be 32-Ohms! I’m pretty sure you wouldn’t even hear anything out of the subs with that high of a load.
On the other hand, if they were wired together in parallel, the total load would be 0.5-Ohms. This is getting dangerously close to that short circuit scenario we talked about earlier. You would be hard pressed to find an amplifier that advertises that it is 0.5-Ohm stable.
To solve this problem, we’re going to get a little tricky and use a combination of series and parallel wiring. There are two useful methods we can use, series/parallel and parallel/series. I’ll show you how to do both so you can see how it’s done, and what kind of results you might expect.
In this wiring method, the voice coils of each subwoofer are wired together in series. You then treat these series combinations as a single voice coil and wire each subwoofer together in parallel.
I know this sounds confusing but it’s really not bad in practice. At the end of this post, there will be a list of diagrams to look at for all types of different configurations.
To calculate the total load, break it down into the same two steps we used for wiring. First determine the total impedance of each individual subwoofer with its voice coils in series.
Each voice coil is 4-Ohms so the total impedance of each subwoofer is 8-Ohms.
Now treat each subwoofer as a single 8-Ohm voice coil sub and calculate the total load with the four of them in parallel.
So the total load of the four dual 4-Ohm voice coil subwoofers connected in a series/parallel configuration is 2-Ohms.
For a parallel/series configuration we will use the same concepts but opposite wiring methods. The two voice coils of each subwoofer are wired in parallel, then each subwoofer is connected in series.
To calculate the total load, first determine the impedance of each subwoofer. Since the voice coils are wired in parallel, and there are only two voice coils, we can use the simplified formula.
So the total impedance of each individual subwoofer is 2-Ohms. Now calculate the total of all four subwoofers connected in series.
The total load of the four dual 4-Ohm voice coil subwoofers connected in a parallel/series configuration is 8-Ohms.
Subwoofer Wiring Size
For systems with less than 1000 Watts RMS, 16-gage speaker wire is adequate. If your system has 1000 Watts RMS or more, you should upgrade to 12-gage speaker wire. These are just some suggested guidelines for minimum wire size. Feel free to upsize the speaker wire if you so choose. As long as the wire fits in the speaker terminals, you won’t harm anything by going as large as you like. Just remember, when it comes to wire size, the larger the gage number, the smaller the wire.
Designing the perfect amp and sub package takes planning. Getting the right amount of power to the subwoofers and impedance matching will ensure that your subwoofer not only sounds great, but also lasts.
If you need some extra help with how to wire your setup, check out the links below for wiring diagrams for a variety of combinations.
Need help with a setup that isn’t on the list below? Leave a comment and I’ll help you out!