Why Two Subs are Better than One (or Three)
We often recommend dual subs around here. In fact, if you spend any time on the Internet researching home theater, you’ll find that dual subs are often the suggestion. There are some very technical papers that describe why (check them out here), but we thought we’d run you through, in layman’s terms, why having two subs is better than having one or even three.
When you first create your home theater, the goal is to get a big picture and lots of sound. You want that cinematic experience in your home. But after the initial “wow” wears off, you start to worry about quality. It isn’t enough just to have a big picture, it has to look good as well. Lots of sound is great, but accurate sound is better. Sure, you can buy a subwoofer that can crush a room, but what good is it if it is so uneven that it overshadows the rest of the soundtrack?
What a Single Sub Can Do
Bass is a fickle thing and very hard to get correct in a small room. If you want the bass to sound good in your room, you have a decision to make. Do you want it to sound good in one seat, or multiple seats? If you are the only one in your theater, then you can use the subwoofer crawl and set up one sub to sound as good as it can at that seat using your room correction program on your receiver.
At that one seat, the bass can sound fairly uniform and even. But if you stand up and move around the room, or even switch to another seat on the same couch, you’ll notice massive differences. In one seat, the bass may seem to disappear, and in another, it may be so loud as to be deafening. But in that one seat, it will sound pretty good.
Two Subs are About Uniformity
As we’ve described before, bass sound waves are extremely long. Upwards of 50+ feet. Those waves are bouncing around your room before you can even perceive them. As the waves bounce, they interact with each other. For a long time, those interactions were not well understood. Enter Dr. Floyd Toole et. al. He and his crew did a bunch of mathematical modeling partnered with real-world testing to try and predict how subs and the room interacted to create the bass you hear.
The TL;DR version is that it is mathematically possible to predict the best locations for your subs. The midpoint of opposing walls (left/right or front/back) is the “best” location. Opposing corners (front left/rear right or vice versa) is second followed by any mirrored location. So, if you place one sub on the front wall three feet from the side wall, the second sub should be placed on the back wall three feet from the opposite side wall. All this is assuming you have an enclosed, rectangular room.
When you place your dual subwoofers in these locations, the bass will interact in more predictable ways. When you move around your room with a single sub, you noticed huge variations. With dual subs, the different locations within the room will sound more similar.
Enter Your Room Correction Program
We said “more uniform” and not “more accurate” for a reason. As you move from seat to seat within a room with two subwoofers, you are unlikely to notice “flat” bass. Flat means that every frequency is playing at the same volume. Flat is what we want, but subwoofer placement will not get you all the way there. What it will do, is make the inaccuracies within the room more uniform. If you have a bass boost at 60Hz at your main seat, with dual subs you likely have a bass boost at all the seats. It might not be the same intensity, but it will all be boosted.
This is important because of how room correction programs work. Modern room correction programs ask you to take multiple measurements at different points in your room (they say “seats” but that isn’t really what they want – check out this interview with Chris Kyriakakis of Audyssey for more information). What they are looking for is inaccuracies that can be corrected. If one measurement shows a boost at a specific frequency, but another shows a dip, the program can’t do anything. If it tries to correct the boost, it’ll make the dip worse. If it corrects the dip, the boost will get worse. So it does nothing.
By adding the second subwoofer and placing them both properly, the inaccuracies are more uniform across all the measurements. This gives the room correction program the ability to adjust your bass response so you get the even response that we are all looking for.
But if Two is Good, Three is Better?
Yeah, no. Just like having one sub is worse than having two, adding a third has a similar effect. While two subwoofers will make your bass response more uniform, the third adds back in the inaccuracies. This is one case where more is not necessarily better.
That said, four subs are better than three, two, or one. The benefits of two subs is even greater when you add two more. Now, you have to place them correctly (exactly the same as adding two more subs). Most people choose either center points of all four walls or, more commonly, all four corners. But the unifiormity will be increased even more and your room correction program will have even more to work with.
Do You Really Need Four Subs?
The improvements you hear going from a single sub to two, are pretty huge. You may think your bass has disappeared at first because of how many inaccuracies were corrected. But going to four subs will be a much more subtle change. One that you are unlikely you notice at the main seat or even most of the seats. We highly recommend you run two subwoofers. Four subwoofers are nice, but we usually recommend them only for very large theaters.
Do you run dual subs? Did you experience an improvement in your bass? Let us know in the comments!