Today’s music and movies can contain a lot of bass. Some large, floorstanding speakers can accurately reproduce the bass found on most music. However, for movies there is a separate channel of sound just for bass, call the Low Frequency Effects channel, or LFE for short. Although the LFE can be directed to the system’s main speakers, I strongly recommend at least one subwoofer for any home theater system. Yes, you read that correctly…at least one. No I am not just trying to sell you more speakers. In fact, if you have a budget in your system for a subwoofer you will usually be better off spending it on two, smaller subwoofers rather than one large one.
Why, you ask? I was just about to explain. Bass below a certain frequency, about 100Hz, is non-directional; you cannot tell where it is coming from. Unfortunately, bass is not uniform. In other words, the amount of bass we hear can vary significantly based on the placement of the subwoofer in the room and your primary seating location. If you are going to be watching movies mostly by yourself, I can help you find the place where the subwoofer will sound the loudest. Place the subwoofer on the floor, right where you will be sitting. Play something with deep, repetitive bass. Some receivers and processors actually have a low frequency test signal as part of their setup menu. Now move around the room and the find the spot where the bass is the loudest. Put the subwoofer there and go sit down where the subwoofer used to be. The bass will be just as loud!
It’s called the Law of Acoustic Reciprocity, and it works. If everyone in the room experiences that same level of bass, consider yourself very lucky. However, typically that is not the case and the amount of bass varies from spot to spot. Sometimes as little as a foot of movement can make the difference between great bass and seemingly no bass. With the first subwoofer placed as above, try moving around the room and see how consistent the bass is. That’s the problem; it isn’t.
Here’s where a second subwoofer comes in. It should be placed in a completely different spot in the room. For example, if the first subwoofer is in the front right corner, place the second subwoofer at the back of the room and away from a corner. How far? Try the halfway point first. Avoid odd fractions of the wall length; they won’t help as much. As for that first subwoofer you placed in the corner, you might try moving it as well to the halfway point of the front or side wall. You might get a little less bass in the prime listening spot, but smoother bass throughout the room.
- Jeff Cowan (guest contributor and all-around audio guy)
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