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Bass Management 102: Great Lows for Home Theater


Tom Mathew

Here we go again!
Getting great bass out of your home theater system
What's home theater without great bass? Fine tune your system to get the roar and rumble!

This article is part two of a series on home audio bass management. The first one dealt with bass management for stereo sound, while this one tackles the same issue with regards to home theater. Life is, of course, more complicated with home theater as you have a receiver, a subwoofer, and at least five speakers to deal with. As was the case with stereo sound, the key to getting great bass out of a home theater system is knowing your equipment and making good decisions based on what you know. Check the manuals for details, and don't be afraid to experiment.

Setting up your receiver
Dolby? Digital receivers give you a number of options for setting up your home theater, including some control over how to manage the bass. This process can be confusing, but the upside is that once you find a configuration you're happy with, your receiver will remember it. So, you won't have to go in and monkey with the settings every time you pop in a DVD.

For the five Dolby Digital channels that play the full range of frequencies (that is, the front speakers, center channel, and surrounds), you will be given the choice to set them to "Large" or "Small" in the receiver. A "Large" denotation tells the receiver to send a full-frequency signal (including bass information) to that speaker. A "Small" denotation tells the receiver to filter out the bass sounds (usually below 150 Hz) and direct them elsewhere.

The important part here is to assess your speakers' ability to produce low-frequency tones. For example, if you have big, powerful tower speakers in the front, and relatively wimpy surrounds, you would set your front speakers to "Large" and your surrounds to "Small." Your towers can probably handle a full-frequency signal, whereas the bass frequencies sent to your wimpy surrounds would be partially (or totally) lost. The "Small" setting on your surrounds tells the receiver to re-direct the bass to a different channel that (hopefully) can do the job. Where does the "Small" speaker bass go? Read on!
The LFE signal: the ".1" in 5.1 sound
Receiver's line-level subwoofer output
All home theater receivers have a dedicated preamp-level subwoofer output. It's the easiest way to put the ".1" in 5.1 sound.

There is one additional selection to make when configuring your home theater receiver: subwoofer "On" or "Off" (or sometimes "Yes" or "No"). The ".1" in a 5.1 (or 6.1 or 7.1) movie soundtrack refers to the "low-frequency effects" or "LFE" channel — in other words, a discreet channel of deep bass . When you select "On" for your subwoofer, you're instructing your receiver to send the LFE channel to your receiver's line-level subwoofer output jack. If you select "Off," then the receiver blends the LFE information into the signal sent to your front speakers.

When you choose the subwoofer setting in your receiver, you're not just affecting the LFE channel. You're also telling your receiver where to send the filtered bass from your "Small" speakers. If you set your subwoofer to "On," the bass that your "Small" speakers don't get is re-routed to your subwoofer; if the subwoofer is set to "Off," the bass is sent to the front speaker-level outputs.

Putting the bass in home theater
Check out the following questions — some may apply to your system, and if they do, they'll hopefully offer some hookup strategies for getting great home theater bass.
Home theater is just not the same without a subwoofer
For rib-rattling bass, nothing can take the place of a mighty powered sub!

1. What if you don't have a subwoofer?
Well, if you don't have a subwoofer, you should get one, plain and simple. Home theater is just not the same without one. But if space or money constraints prevent it, here's what you do: go into your receiver's menu and set the subwoofer to "Off" and the front speakers to "Large." The LFE signal, as well as the bass from speakers selected as "Small," will be diverted to your front speakers. If you have really beefy towers in the front, then you might experience something resembling home theater.

2. What's the easiest way to hook up a subwoofer for home theater?
Connecting your receiver's subwoofer output to your subwoofer's LFE input is the easiest way. The LFE input is a line-level (preamp) connection that bypasses the subwoofer's built-in crossover filter. Opinions certainly differ — bass management is, at times, tweaky stuff, and often it just comes down to personal preference. But a connection to your powered sub's LFE input should provide your DVDs with sufficient roar and rumble. Unfortunately, not all powered subs have an LFE input.
Every powered subwoofer has a line-level input
From LFE inputs to speaker-level inputs to crossover filters, most powered subs give you lots of options.
3. What if you have a subwoofer, but it doesn't have an LFE input?
All is not lost. Every powered subwoofer on the planet has a line-level input. There are two kinds — one's called "LFE" and the other's called "Normal" or "filtered" or, if there is no LFE option, it might just be labeled "line in." The only difference between the two is that the LFE input bypasses the sub's internal crossover filter, while the Normal input does not. Most subs nowadays have both (sometimes it's a single input with a "Normal/LFE" or "Filtered/Unfiltered" switch that lets you choose between the two).

Some subwoofers only have a Normal line-level input, so you cannot bypass the sub's internal crossover filter. Since the LFE signal is already filtered (usually at around 150 Hz) before it even reaches the sub, you run the risk of your sub's filter interfering with and potentially degrading the LFE signal. Plainly put, two crossover filters fighting with each other can create some very bad sound.

You might be able to get around this problem quite easily. Most (but not all) powered subs offer what's called a "continuously variable" crossover filter, which means there's a dial that lets you adjust the crossover point by single-hertz intervals. Try setting your sub's filter to the highest crossover frequency it will allow, and then take a listen. If it's far enough away from the crossover point of the filtered signal, there might be little or no interference. If so, set the subwoofer to "On" in your receiver, and the line-level LFE signal as well as the bass from "Small" speakers will still go to your sub.

But let's say you can't make your sub's crossover play nice — now what?

4. Is it possible to hook up your subwoofer for home theater if you can't get a satisfactory line-level connection?
The answer is proooooobably. Most (but not all) powered subwoofers have speaker-level inputs and outputs. To make a subwoofer speaker-level connection, just hook up the sub via your receiver's front speaker-level outputs. Then, hook up your front speakers via your subwoofer's speaker level outputs. It's basically a daisy chain from your receiver to your sub to your front speakers.

This configuration will only work if you set your subwoofer to "Off" and your front speakers to "Large." By doing this, a full-frequency signal (including the LFE and the bass from "Small" speakers) will go to the receiver's front speaker-level outputs and on to your subwoofer. The sub's built-in filter will block the higher frequencies and produce only the deep bass. Then, your sub will pass on the unfiltered full-frequency signal to the front speakers.

Some would argue that a speaker-level connection would introduce noise into your low frequencies, and that may very well be the case. But if you can't get a proper line-level connection, or you just want to hear how it sounds in comparison, give it a try.

Tweaking the system
OK, so home theater bass management is not a walk in the park. But taking the time to get the best settings and configurations can have a dramatic affect on your system's performance. Don't make the mistake of thinking that just because sound is coming out of all the speakers in your system that everything is hunky dory. You might only be tapping a fraction of your system's potential. Try a few different setups and see what sounds the best. And while the task might seem somewhat daunting, you don't have to be an electrical engineer to tweak the bass in your home theater system. You just need ears and a little patience.

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