How to Set Up a Subwoofer

This article is part of our Home Theater Design Series that covers virtually everything about designing a home theater.

Adding a subwoofer to your home stereo system or home theater system can make a huge improvement in your sound if you know how to properly position the subwoofer and adjust all of the settings. If you are willing to spend just a little bit of time learning how to set up a subwoofer the right way, the addition can transform your system. You might get lucky if you just plop it down, turn it on, and everything winds up perfect, but odds are you’ll need to play around with placement and adjustments to get ideal results.

The main reason people add a subwoofer is the obvious one: you will normally get deeper, and more, bass output. What you may not realize, however, is that adding a subwoofer can also improve the midrange and treble definition of your main speakers. Although, there is a risk of a sub addition making your main speakers sound worse if you just drop one in without some tuning.

We will look at a few different types of cases where you might add a subwoofer. Home theater systems, home audio systems, or adding a sub to a pair of powered speakers all will have some similarities, yet some differences in how you go about getting the best sound.

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Subwoofer Basics

Ask any acoustician what makes the biggest difference in your sound and they will tell you the room. Every room is different, not only in how the materials in the room reflect or absorb sound, but did you know the dimensions of the room can have a big effect on the sound of your subwoofer? As the bass frequencies bounce around in your room, they can build up at certain parts of the room and cause peaks and dips. To experience what we mean, if you have a subwoofer now, put on a track with some consistent deep bass and just walk around your room. You will probably notice that there is a lot more bass in the corners of your room than exactly in the center of your room. Even if you don’t have a subwoofer, you can do this test and experience the similar results.

Where you sit in your room and where you decide to place your subwoofer will affect how you experience these peaks and dips in bass response. First, if you have some flexibility in your seating position, it is best to have your couch or listening chair about two-thirds of the way back into the room. By placing your listening position against the back wall, you will hear more exaggerated bass, and alternatively, in the dead center of the room, you will likely hear less bass.

The same holds true for where you place your subwoofer. Putting your subwoofer directly in a corner will give you the most bass output in the most places in the room. So, there is a fine line to walk between where you sit in the room in relation to where you place the subwoofer. You’ll typically get smoother bass response if you move the subwoofer away from the corner but keep it near a wall.

As you can see, experimentation is key. Also, you might have one of the newer subs from JL Audio, Martin Logan, Paradigm or more that offer some form of room correction. These systems are great for allowing you to place the sub where it has the most output, and then using the EQ system to take out the peaks and smooth things out. Remember, you can cut down a peak electronically, but you can never fill in a dip, so placing your sub where it will have good room-filling output is easier if you have one of these new breed of subs with room EQ built-in.

If you are a more critical listener and enjoy closing your eyes and imagining the performers are in front of you, there is a need to make sure your new subwoofer and main left and right speakers are in sync. This is best accomplished by having the front of your subwoofer parallel to the front of your left and right speakers. Most home theater processors will allow you to do this electronically by adjusting the distance in the setup menu for your main speakers and subwoofer, but most two-channel rigs don’t have this option.

The Magic of a Sub for Midrange and Treble Improvement

You would normally think that adding a subwoofer to a system would just add deep bass, however, if done properly, it can also make a huge improvement on how voices and other instruments sound. Most speakers have drivers (the speaker components) that have to not only handle the deep bass, but also handle the upper bass and lower midrange at the same time. Some two way systems put a lot of the frequency range through the woofer. If you set your subwoofer up in such a way that takes away the deep bass frequencies from your main speakers and sends them to the subwoofer, which is really better made to handle them anyway, then your speaker will give a sigh of relief that it no longer has to strain to try and reproduce deep bass. This means, especially in a two way system, that the woofer is not asked to move as far to produce bass at the same time it’s trying to reproduce midrange, and as a result, the middle frequencies will just sound much clearer.

If you have some fairly large speakers and take the bass away from them by sending it to a sub, you may also hear some treble and imaging improvements. By reducing the bass in the speaker cabinet, you will lower resonances, which in turn will improve your treble clarity.

It’s all pretty magical how you can actually improve all aspects of your sound by adding a subwoofer the right way!

Now let’s look at a few use cases.

How to add a subwoofer to a small pair of powered speakers

Powered speakers are extremely popular right now because they reduce clutter, can sound really good, and many have several input options. Another trend we are seeing on powered speakers is a subwoofer output jack. This allows you to add a subwoofer to your small powered speakers. As we have talked about above, you should get not only deeper bass from the sub, but better midrange and treble too. So what is the best way to set this up? First, you’ll need to see if your powered speakers have just a stereo line level output or a true subwoofer output. If it is a stereo output and not labeled as a subwoofer out, you’ll need to make sure when you connect those jacks with a cable to your subwoofer that you engage the crossover of your subwoofer. You’ll probably want to experiment here on the frequency, but we think you’ll find it sounds best set between 80hz and 120hz for most smaller powered speakers. This should be clear on the back of the subwoofer.

If your powered speakers have something labeled “subwoofer” out, it is likely this output already has a filter on it at the right frequency. If this is the case, when you connect to your subwoofer, set the crossover on the subwoofer to bypass so you are not double filtering things. One way to tell if the output is actually filtering is to play some music with vocals in it, and if you hear the vocals coming through the subwoofer, then it is not filtering and you should use the subwoofer’s crossover.

In either case, if you can, position your subwoofer on the same wall as your main speakers. If you line it up with your main speakers, you may enjoy an improvement in imaging. Once you have things set up, you’ll need to experiment with the level control on your subwoofer to blend it well to your speakers. You want to feel that extra bass, but you do not want it to overwhelm the rest of your music. We suggest you pick a track with acoustic bass and vocals. Turn up the level in small increments until the bass sounds like it is at a similar volume to the pluck of the bass that should be coming from your main speakers. If the bass ever starts to sound like it is overwhelming the vocals then you have it too high. It’s fun to experiment to fine tune things!

How to add a subwoofer to a two channel audio system

Most of the same techniques we have discussed above will apply here. Some stereo receivers or integrated amplifiers will have a subwoofer output to allow you to add a subwoofer to your system. Some will even let you go into a menu and take the bass away from your main speakers and send it all to the subwoofer. Or, you may have a component that has a set of preamp outs that let you run the full signal over to a subwoofer. If this is the case you will definitely want to use the crossover in the subwoofer.

Most of the better subwoofers will have both an audio input and output. This allows you to send an audio signal that is full range into the subwoofer input, use the subwoofer’s crossover to select the signal that stays with the subwoofer, and then send the filtered signal out to the amp driving your main speakers. This will usually only work if you have a separate preamp and power amp, but can work really well to reduce the bass going to your main speakers and give you that open midrange. Just be sure to run high-quality cables in and out of the subwoofer so you have no signal loss.

The placement and set up suggestions we have for this type of system are the same for how to set up a subwoofer with a set of powered speakers. Try to keep the sub on the same wall and ideally the same plane as your main speakers and then experiment with the level. Typically for most speakers the best crossover point to set will be around 80hz. Then go through the listening suggestions we have in the section above.

Adding a subwoofer to a home theater system

This use case is actually the easiest one to implement. All home theater receivers or processors will have a setup menu that allows you to tell the system that you have a subwoofer. When you do this, generally you will want to tell the system your main speakers are small, which should automatically set the crossover to 80hz, or if you have a choice of adjusting the actual frequency, we suggest you start at 80hz. This gives you the magic of taking the bass away from your main speakers and helping them open up! You will also want to make sure you adjust the distances. Use a tape measure to find the distance between your main speakers and your primary listening spot, input that, and do the same for your subwoofer and all of your other speakers.

Some home theater receivers have an auto calibrate mode that can do a great job with correcting room issues and helping with set up, but we have found most of them to be inaccurate in finding the distances for the subwoofer. If you run any kind of auto calibration, be sure and double check the distances after you run it.

Your home theater system will also give you a big head start on getting the levels adjusted. You can do this by ear or by simply downloading a good app for your smartphone that measures “SPL”. There are several on the market that work really well. You then play test tones through your home theater and adjust the levels until they are equal. After doing this, feel free to experiment with the levels and crossover.

In a good home theater, you will also want to experiment with the crossover of your center channel speaker. Sometimes, setting the crossover to 90hz or 100hz will really clean up the voices, especially if your center channel is sitting inside some kind of cabinet. It's great that you have a subwoofer you can route those deep bass signals to, which takes the load off your main speakers!

More than one subwoofer, yes or no?

The answer is absolutely--add as many as you can! Remember those standing waves we talked about? Well, when you add multiple subwoofers to a room, those effects are greatly diminished and everything just cleans up. Without getting into the detailed mathematics, each subwoofer you add into a different location gives you the ability spread bass move evenly throughout the room which can dramatically improve the experience across a couch or set of theater seats. Some of the best home theater systems we have ever heard have had 4 or more subwoofers! Learn more about how to optimize the placement and set up of a subwoofer in a home theater system.

We hope this gives you a good starting point to understanding how to set up a subwoofer, and why adding one (or more) to your system can offer you big improvements.

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