The One Ring is cut from Sauron’s hand by Isildur. Engines ignite as the Apollo 13 spacecraft launches into space on the Saturn V rocket. Sam Flynn battles on the lightcycle grid for the first time.
These are dramatic and pivotal moments in The Lord of the Rings, Apollo 13, and Tron: Legacy, respectively. And they all utilize low frequencies with sound effects or music (or both) to make the experience visceral, bringing the movie to another level.
Without proper subwoofer coverage in a home theater or living room, the presentation will be lacking, whether you’re aware of it or not. Even if you have full-range front speakers with low bass extension, they’re likely not able to reproduce the lowest frequencies found on a movie’s soundtrack. Plus, the placement of those speakers is optimized for stereo, surround, or Atmos sound, not for the best low-frequency performance.
To get a truly cinematic experience in your home, a subwoofer is a necessity. But what about more than one subwoofer? What benefits do two or more subwoofers deliver?
One subwoofer: Boom
Having a single subwoofer in your system is an important step towards hearing the complete sonic intent of a movie. And for many, one subwoofer is the most you’ll ever have in your setup, as the best soundbars like the Samsung HW-Q990F only come with one sub and can’t be expanded. Even if you have a custom, component-based home theater speaker setup, you might only have the space or money for a single sub.
In my case, my SVS SB-1000 Pro sub supports an SVS Ultra Evolution speaker system and delivers satisfying, full bass in my living room. But even with a great performing sub, having only one in a room can lead to a few issues. While bass frequencies are generally omnidirectional, depending on how close the sub is to your listening position, it can be possible to discern where the bass is coming from. And this localization of bass frequencies can distract from what’s happening on the screen.
In addition, no matter where a sub is placed, a single sub will inevitably create standing waves. This happens when the direct sound wave and a reflection of the sound wave meet, with the result being either a boost to the frequency (when the wave forms are in phase) or a dip at that frequency (when the wave forms are out of phase and cancel one another).
These are also called peaks and nulls. When someone refers to a sub being overly boomy, or the bass gets sucked out of the room, it’s likely because of the standing waves created by subwoofer positioning.
This can be helped with room treatments or room correction software that is now commonplace in surround sound processors and AVRs. But another method to help with standing waves and localization is by adding a second sub.
Two subwoofers: Bada boom
If your space allows for it, two subs are ideal for most rooms, as that configuration will start to clear up the single-sub issues discussed above.
Even when it's in the most ideal position in your room, as mentioned, standing waves caused by direct and reflected bass waves will result in peaks and nulls in a sub’s frequency response. So some frequencies will sound louder, in the case of peaks, or softer, where there’s a null. A second sub, in a different location, will have its peaks and nulls at different points on the frequency curve, and when the response curves of the two subs are summed together, it leads to a more even response with more accurate bass across the frequency range for the room.
Having multiple subs in different parts of the room also means the bass is no longer coming from only one direction, so localization is reduced and there is a larger listening sweet spot – potentially enough to cover an entire couch instead of the single seat directly in front of the screen.
Promotional photos used by speaker makers would have us believe that having both subs in the front of the room is the ideal setup. While it’s certainly not a bad choice, especially for aesthetics and to keep cable runs to an AVR short, when it comes to overall performance, it’s better to place one up front and one in the back in opposite corners of the room.
It’s also important to make sure your AVR or processor supports multiple sub outputs, or that your subs have outputs, so you can daisy chain connect them. And always run your room EQ software — be it Dirac Live (my personal favorite), Audyssey, or a proprietary system — to help correct issues with your room.
All the subwoofers: Big bada boom
More is always better, right? Well, when it comes to subwoofers, only to an extent. When you have more than two subwoofers in your system (usually topping out at four in a home theater for non-millionaires), you’ll continue to get many of the benefits when going from one to two subwoofers.
Additional subwoofers will have different peaks and nulls than the original sub or two because of the effect of the room, allowing for an even smoother overall frequency response and more accurate low-frequency performance. There’s also even less potential for localization when there are more than two subs, since the sound will be coming from more directions.
With more subs comes more potential power. This is great if you have a large theater room you’re trying to fill with sound, and it also means that for a mid-sized room, you can get smaller subs, which take up less floor space and might be easier to fit in with your decor.
There are diminishing returns beyond two subs, though, when you take into account the extra space required, as well as the extra cost. If you’re a huge fan of bass or have a big theater, it’s worth considering putting more than two subs in your room. For the rest of us, I’d recommend sticking with two.
No matter what you decide — whether it’s one, two, or 16 subwoofers — the important part is that you have a subwoofer in your system. After purchasing a new TV and speakers, the bass performance is usually an afterthought, if it’s even thought of at all. But once you experience thumping, expansive bass in your home, your movie-watching life will never be the same.
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