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Bass Basics: Adjusting your home theater subwoofer

 You've just fired up a DVD on your new home audio system. The screen momentarily goes blank: here comes the main feature. No — it's a THX demo! (You weren't expecting that.) Imaginary objects zip around your head in 3-D space...this is promising. And then that famous tsunami-wave of sound, THX's audio "logo"....But wait, where's the bottom-end? Where's the spine-tingling bass?

If your home theater system's bass output sounds too lean, or if it's muddy and distorted, a few key settings on your powered subwoofer and receiver can make all the difference. Here are a few tips to help you get your sub performing at the top of its game.

Set the crossover point

For the best possible sound, you want your front, center, and surround speakers to play only the frequencies they can handle, and your powered sub to play the rest — the deep bass frequencies. That's the job of your system's crossover. To use a common analogy, a crossover works sort of like a "sonic traffic cop," sending the right frequencies to the right speakers. But where should your sub leave off, and your other speakers begin?

To determine the optimum crossover point for your system, you should know what frequencies your main speakers can handle. In my own system, I've got small satellite speakers all the way around. The owner's manual told me they could go down to about 120 Hz, and I set my system's crossover accordingly. (For larger speakers, this number is usually lower — it's not uncommon for bookshelf speakers to get down to 50 or 60 Hz, for example.) Once you've set your crossover frequency to one that matches your speaker setup, sit back and give a quick listen. You can even experiment by adjusting the crossover frequency a little bit one way or the other...after all, what matters is getting your system to sound good to you.

Check your subwoofer's "LFE" setting

What some folks may not know is that their system probably has two subwoofer crossovers, one inside their surround sound receiver and another built into the powered subwoofer itself. And these two crossovers don't play nicely together. If they're both engaged simultaneously, you're probably not getting all the bass that you could.

That's where your subwoofer's "LFE" setting comes in. This acronym stands for "Low Frequency Effects" (not "Loud Family-room Explosion" or "Looking For Explanation"). "LFE" is just the technical name for your home theater receiver's bass channel. This setting tells your subwoofer whether to use its own built-in crossover or the one inside your receiver. In most cases, the latter is the better way to go. That's because most home theater receivers these days have advanced digital bass management that not only tells your subwoofer what frequencies to play, but also tells the rest of your speakers what frequencies not to play.


This Polk Audio subwoofer has a separate unfiltered "LFE" input for use with a home theater receiver.

The LFE control lets you bypass your sub's built-in crossover, so you can use the filtered signal that's coming from your home theater receiver's dedicated bass channel. Some subs accomplish this with a switch that lets you toggle between LFE (unfiltered) and "normal" (filtered) mode, while others have a separate unfiltered LFE input. And if your sub doesn't have either one of these, don't worry — just turn its crossover dial all the way up to help ensure that it won't interfere with your receiver's built-in bass management.

Find the level that sounds best

Finally, there's your subwoofer's level control. It's a straightforward concept, no doubt. But this setting makes a big difference, so it's worth spending a few minutes tweaking and listening to get it right. Keep in mind that more bass isn't necessarily better bass. Try starting at a lower level and gradually bumping it up to where you're feeling plenty of punch, without sacrificing clarity. If you resist the urge to crank your sub's level control way up past twelve o'clock, you stand a better chance of achieving tight, clean bass, and well-balanced overall sound.

Of course, it's all a matter of taste. I'll admit that, for my own part, I probably tend to push my sub a little bit more than others might. But then again, when I pop in a THX-mastered DVD, and that huge-sounding THX demo kicks in, it's like audio nirvana.