Why you don't need two subs

By now you've heard it said many times "two subs are better than one." So it might come as a surprise to hear it's not always the case. Quite often it's the wrong advice. The answer is not quite as simple as the one most audiophiles seek. People like simple ideas that make intuitive sense. This is why myths in audio are so prevalent - they are simple ideas that seem to make intuitive sense, so they spread on forums. When something makes sense, people are reluctant to change their minds. My aim with this post is to arm you with the information to help you make a better choice for your particular situation.

The case for more than one subwoofer

There are only two technical reasons for more than one sub:

1. Output - you want more clean output than a single sub can provide
2. Smooth response - no single sub position can provide a smooth response in the seats that matter

There are many non-technical reasons, but I'm going to stick with what provides an audible benefit for your dollar.

If your goal is to increase output, it's worth keeping in mind that two subs can work against each other. Here is an example:

These two sealed subs have a different response due to their positions. How do they sum when measured together?

Here you can see that in the low bass range, below 43 Hz they actually  provide a less smooth response and lower output than just a single sub in the blue position!

This is where things work against those who buy subs, put them in the room and hope for the best. The point to take away here is that the benefit is not automatic. You can't simply put multiple subs into a room and get the benefit so many are talking about.

So you might be wondering when I'm going to present the case for more than one. Here it is. There are many rooms where one sub isn't enough. Here is a good example of a room that requires two.

This was a fairly typical dedicated rectangular room, with one row of seating in a good sized room. This client came to use looking for the missing midbass punch. The interesting thing here was that they didn't put it quite that way. They initially believed that they were missing bass depth. They had one sub up the front of the room:

The large peak around 26 Hz is provided by the room and it allowed a small sealed sub to punch beyond its weight. It achieved good output to near 20 Hz. But the real problem was in the midbass. There is a large recess around 30 - 45 Hz. In movies a great deal of the action lies in this range. I'd argue this region is more important than 20 - 30 Hz. We tested every possible position in this room. No single position could provide a smooth response. Hence we changed our focus to finding two positions that would work well together.

Along the front of the room, we found a better position:

Moving this sub, we removed a dip to achieve smoother upper bass. Then we found a position for a second sub that just happened to be under an existing coffee table that was large enough to hide a sub.

The second position solves the midbass punch issue. With these two positions, we now have a chance to fix the bass.

The final result was a dramatic increase in bass authority and dynamics. Movies delivered a more visceral experience that was lacking before.

The case for just one subwoofer

For audiophiles who just want the best bass in one listening chair, I've found that about half of the rooms we test need one sub and the other half are better served with two. Here is an example of one room that suits just one sub. All the positions we tested:

 

As you can see, the positions vary enormously. Here are a few positions that are interesting:

 

This client had many subs in the room, most of them in positions that aren't effective. One of them was in the blue position, which performs very well for 2 channel. The orange position is one of the worst. I've shown it here to give an idea of how badly the room can impact the response. The black position is similar to one that he was using, but you can see it provides a lot more free output. In this room, only one sub is required with moderate EQ.

This room is one of the best I've seen for using just one sub. Yet surprisingly, they had many subs running in the room. The message here is clear - always test the room before you decide how many subs you need.

It's surprisingly common for people who just need one sub to have several. If your plan is to buy a sub then hope for the best, I always recommend just one sub. Where you want to take the next step, my advice is always the same. Test the room. This means either learning how to do it, or engaging a service like ours to do it for you.