You bought a big high definition television that has a beautiful picture. After that, you spent a little money putting together a 5.1 audio system. Movies and games look and sound better than you ever thought they could in your home. Are you finished? Nope. There is still one piece of the puzzle missing before you can enjoy theater-beating sound in your home. A subwoofer.

The range of human hearing is approximately 16Hz to 20kHz. 16Hz is approximately the lowest note a pipe organ will produce. Sub-16 Hz bass is good too, but you feel it rather than hear it. Generally speaking, most floor standing loudspeakers will reproduce from the upper 30 Hz range up to the audible limit. Bookshelf speakers will not plumb as deep, perhap only going as low as 50 Hz, depending on the loudspeaker. If you want explosions to sound like your room is coming apart, if you want to feel the action onscreen, if you want ultra low bass to slam you in the chest, we need a sub that is flat down to around 20Hz.

Not all subwoofers are created equal. There are many, many horrible subwoofers that are pathetic cubes that sit in the corner and make unnatural, feeble booming sounds. Just because someone threw a 12+ inch driver in a box with an amplifier doesn’t guarantee you room shaking bass. Subwoofer design is part mathematics, part craftsmanship. The two things we are really concerned with in a subwoofer are extension, which is how low a subwoofer will go before loosing steam, and output, or how loud the sub will play.

More so than usual, when shopping for subwoofers we really want to pay attention to the specifications. We are going to know a lot about a subwoofer before we ever hear it from getting an idea about it’s extension and output from the specs. For extension, note the stated frequency response. A subwoofer that has a flat frequency response in the desired range is one that is going to produce the sounds in a realistic manner. By flat, I mean that the variance of output over the produced frequency range will only deviate a small amount. Generally, subwoofer makers will give frequency response numbers for what their subwoofers can produce within a 3 dB (decibel) variance, so what we are hoping to see is +/-3dB from 20Hz-100Hz, which would look something like this:

Actually, the subwoofer from the above chart does +/-3dB from about 23Hz-130Hz, but you follow what I’m saying. The response is flat, so no part of the produced frequency range will be overemphasized or anemic, and will be delivered in a natural manner.

For output or max SPL, a dB number will be given, which represents the subwoofer’s maximum output. We want at least rock concert level. 105+dB, and this is an instance where more is better. Some manufacturers don’t state the max SPL. In that case, we want an onboard amplifier that puts out at least 300 watts.

AV receivers and pre/pros (preamp/processors) will give you a crossover point to set for your subwoofer. This is the point at which your loudspeakers hand off to the subwoofer. This takes some strain off your loudspeakers. They are able to do a better job at reproducing midrange and high frequency sounds when they aren’t trying to muster the deepest tones the track is calling for. Your subwoofer might be able to reproduce 120Hz notes, but your loudspeakers are better off doing it. The THX standard specifies a subwoofer crossover point of 80Hz, and that is perfect for almost everybody.

So you’ve done your homework and found a subwoofer within your budget that will drop low notes like depth charges hitting a submarine. After hooking it up to your equipment there are two important steps you need to take to get the most out of your new subwoofer.

The first step is finding the right placement. We have to find the right spot in the room for the subwoofer. Rooms can often either eat bass, or amplify it, and we need to figure out how the space the subwoofer occupies affects it’s performance. Generally speaking, subwoofers like to be near a corner of the room. Low frequency sounds are non-directional, so while most people probably situate their subwoofer in the front of the room, the back will work if you’re space-constrained. If you are getting boomy bass, try pulling the subwoofer away from the wall a little. If the bass seems a little weak, try sliding that subwoofer closer to the walls in a corner. Experiment. This is an area where I can’t tell you exactly where to place the sub. Every space is different. Centimeters can make a huge difference. You will have to move the subwoofer around to find the best spot for it.

That done, we need to adjust the output of the subwoofer to match the rest of our loudspeakers. Many of you with newer AV receivers will not have to worry about this. Newer receivers from just about every manufacturer come with built-in room tuning software. This will get you darn close, at least close enough that in most cases you won’t need to buy any additional equipment to fine tune.

For those of us whose AV receivers and pre/pros don’t have built-in room tuning equalization, we need to procure an SPL (sound pressure level) meter. An inexpensive SPL meter can be found at Radio Shack, or on ebay. SPL meter in hand, we want to set the meter to “C” weighting. Turn your system up to the volume you watch movies at, and position the meter where your head sits during movie viewing. Using the built-in test tone on your receiver, cycle through all six channels of your 5.1 channel system, and make the necessary adjustments so that your loudspeakers are all putting out the same dBs at the listening position. Now, do the same for the subwoofer, but in this case, set the subwoofer about 5 dB louder than your speakers (if your speakers all register 70dB, adjust your subwoofer gain until you get 75dB with the test tone).

By spending a modest amount of time spent tailoring your system’s output to the room, your 5.1 channel system is now going to produce sound that is not only three dimensional, but will rattle the windows in their panes when called upon to do so.

Having a capable subwoofer will enhance your movie enjoyment greatly. There’s nothing like feeling the “thud” of the approaching T-Rex in Jurassic Park, or fearing your house is going to sustain structural damage when you watch a DVD like The Haunting or U-571. You’ll wonder how you managed so long without one, and friends will love coming to your place for movies and games.

Serious subwoofers can cost serious money. There are, however, some subwoofer producers that can provide a less painful entrance into the world of bass addiction. Some recommendations for acolytes of the Church of Bass: If you’re shopping, take a look at the offerings of SVS, Hsu, Elemental Designs or the soon to be available MFW-15 from AV123.

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