Adding a subwoofer can greatly improve your audio system's performance. How big (or powerful) of one should you get?
The real audio power comes from the low end, the bass. When you feel the rumble in your chest, that's bass.
Most of us want this at home, but with myriad subwoofers out there -- and even more specs and sizes -- what's the best choice? Though the simple "the biggest, most powerful you can afford" is easy to say, the correct answer is little more complex.
First, let's go over what we're talking about. A subwoofer is a square(ish) box that supplies all the low-end bass notes in an audio system. Most soundbars and HTIB systems come with subwoofers, but they're often low-powered items.
Can you upgrade?
If you have a wired subwoofer, with a single RCA-style cable running to it, chances are you can upgrade your sub. This could be part of an HTIB, a real 5.1 system, or even a soundbar with a wired sub. Wireless subwoofers that come with soundbars or HTIBs generally are proprietary, and can't be upgraded.
If you have something like the Bose cube speakers, where the speakers connect to the sub, there's likely other processing going on inside the sub, and I would do additional research to make sure you can switch it out without issue.
If you want to add a sub to your system, but don't have a receiver, HTIB, or soundbar with a wired output, you're not out of luck. Some TVs have a subwoofer output (these are rare, however). All TVs have an audio output. Check your owner's manual to see if using the audio output disables the TV's speakers. If it does, sadly, you're out of luck (and should get a soundbar or other audio system anyway).
If it does output audio at the same time as the internal speakers, you can add a subwoofer. The cheapest solution is a wired one, where you take the output of the TV and plug it into the sub. You may need an optical-to-analog adapter for this, which can run in the neighborhood of $25 to $45. You can also do this wirelessly with something like the Audioengine W1, Outlaw Audio OAW3, or subwoofers that come with their own wireless audio transmitters. The trick with this method is tuning the subwoofer's crossover to only produce low-end sounds (generally, under 100Hz is good, 80Hz is very common).
Any discussion of subwoofers is going to revolve around two specs: Driver size and power. We'll get to driver size in a moment. For now, let's talk power. When I sold audio, it was incredibly common for people to shy away from high-powered subwoofers. I get e-mails and comments on other articles that show the same mindset. The thought was, high-powered subwoofers have to be louder than low-powered models. No! This is really important:
A 1,000-watt subwoofer doesn't have to play any louder than a 100-watt subwoofer.
The watt rating is a rough guide to how loud a subwoofer might be able to play, but it doesn't have to be louder. You always control the volume. In fact, a 1,000-watt sub may sound better at "regular" room volumes than a 100-watt sub. Though quite common, 100-watts really isn't that much when we're talking subs. Thanks to digital amplification, 300, 500, and higher wattage subs are quite affordable.
But watt ratings, in themselves, are not a complete judge of a subwoofer's performance. They are just one easily findable spec. There are other factors that you need to consider as well.
Generally speaking, subwoofers are boxes that can fit, just barely, under an end table. Inside is a fairly large driver (the part that makes the noise) and usually the amp that powers it. In order to perform its best, a driver should have some space in the cabinet behind it. So ideally, a 12-inch driver will have a decent size box, while an 8-inch driver could have a smaller box.
The problem is, bass waves are really long, so the driver has to work hard to produce those waves in volumes you can hear. One way to do this is with a bigger driver -- 12 inches is a common size -- but you can find 15-inch models. Some models feature multiple drivers. No, two 6-inch drivers can't equal a single 12-inch, but they'll almost always perform better than a single 6.
The other way is with lots and lots of power. As the driver and cabinet size goes down, the power needs to go way up to compensate. So, in theory, a 8-inch sub in a small box could sound similar to a 12-inch sub in a big box if it had significantly more power.
The cheat-sheet for subwoofer placement is that putting the sub against the wall will add a little bit of volume. Putting it in the corner will add a little more. Either place isn't strictly the most accurate bass response (as in, certain frequencies will be accented over others), but it will get you more volume if that's what you're after.
To get the best bass in your room, sit at your main listening spot, and have someone move the sub. Or, even better, put the sub at your listening position (on your sofa) at ear level (height is important too!), then crawl along the wall till it sounds the best. You'll be amazed how different the bass sounds just a few feet apart. You might get a ton in one place, then move just a few feet forward, and get next to nothing. Because the low-frequency bass waves are so long, they interact with the room itself quite significantly. Room acoustics are cool.
Another option is multiple subs. Again, this doesn't necessarily mean more bass; the goal is better bass. Multiple subs in different locations interact with the room differently because of where they are. Check out Multiple subwoofers: If one's good, two are even better and Brent Butterworth's epic Subwoofers: 4, 2, or 1?, which is probably the best article ever written on the subject of multiple subs.
Steve Guttenberg has written a great article on subwoofer setup I recommend you check out, called, not surprisingly, How to set up a subwoofer.
Certain subs and many receivers have room EQ processing, which plays test tones through your speakers and subwoofer and generates a room-specific equalizer setting. These can do a lot, helping to minimize peaks in the frequency response (over-accentuated notes). They can't fill a gap, however, in frequencies that the room acoustics are making hard to hear. These systems aren't magic. They can't make a cheap, underpowered sub sound like a big high-powered one, nor can they fully counteract the negatives of poor sub placement. They do, however, help, and are worth looking into if you have the option.
Putting it all together
In a small room, a small sub will work just fine (Small, in my parlance, is a 10- or 12-inch sub with at least 100 watts). In larger rooms...not so much. If your room has open walls to the rest of the house, you'll need even more power or a larger sub, as the bass sound will need to fill the entire space. If you have the space and/or the budget, consider multiple subs, as they'll often perform better than a single subwoofer. Placement is crucial, and a little time spent finding the right position can reap huge benefits in bass sound quality.
Good bass vs. more bass (a important last note)
Most people equate subwoofers with the thump-thump they hear from other cars at stoplights. This is bad bass. Volume at the expense of quality. A quality subwoofer, placed correctly in a room, can produce deep sounds realistically, not just the thump-thump. The idea with any speaker system is to accurately recreate all frequencies in the audio spectrum equally. So the best subwoofers don't make a boom sound, but just stronger bass than is possible with small speakers. Good bass isn't necessarily more bass, just better audio fidelity. A more realistic audio representation of what's in the music or movie. If you want to add more bass than that, you can turn certainly turn it up, but the key is that you don't have to.
The problem is, specs alone can't reveal a quality subwoofer over a bad one. They may lead you in the right direction, but a well designed 10-inch, 100-watt sub might sound great, and a poorly designed 12-inch, 500-watt sub might sound terrible. This is where reviews come into play, and are worth seeking out. You can check out our reviews here. Also worth checking out are Brent's extensive subwoofer tests at Sound+Vision magazine, and Gene DellaSala's at Audioholics.
So there's no rule like "12-inch 100-watts for 'X'-size room," but generally speaking, larger, higher-powered subs will probably work better, even in smaller rooms. If you have a large room, or one that's open to the rest of the house, a 12-inch, 100-watt sub isn't likely to cut it. In fact, it's probably safe to consider 12-inch, 100-watt subs as the minimum. Be wary of subs with less than 100 watts, and if the driver is smaller, you'll need a lot more power. There are exceptions, of course, but this should give you a starting point.
Good bass is the first thing most people notice about a home audio system. It easily has the most "wow" factor. That is almost entirely due to the subwoofer. The safest bet is a large sub with a lot of power. You're much better off running a big sub at "4" than a small sub at "10." If you want the best sound, multiple subs, in different locations in a room (or even just in the corners), almost always sound better and more realistic than a single sub.
Though you can certainly improve your sound with just about any subwoofer purchase, if you want to go really hardcore, a local custom installer can probably help you out with installation and placement (there are even some pretty trick in-wall subwoofers).
Got a question for Geoff? Send him an e-mail! If it's witty, amusing, and/or a good question, you may just see it in a post just like this one. No, he won't tell you which TV to buy. Yes, he'll probably truncate and/or clean up your e-mail. You can also send him a message on Twitter: @TechWriterGeoff.