How to Choose the Right Subwoofer
When looking for a subwoofer for your home theatre or listening room, there are a lot of factors to consider. When asked about the difference between sealed and ported subwoofers, and which one you should choose for your room.
First, let’s quickly review the true purpose of subwoofers and how they work in different situations. It will ultimately ensure that you have all the information necessary to choose the right subwoofer.
Why You Need a Quality Subwoofer
Most people think the number one reason for a subwoofer is to get more bass. It’s true that subwoofers do give you more base, but did you know that if properly implemented, the right kind of subwoofer can also improve the overall sound of your main speakers?
Let’s say you have a pair of Bookshelf or smaller Floorstanding speakers. If you are playing them without a subwoofer, they are being asked to create the entire musical frequency spectrum from the lowest lows to the highest highs. To attempt to recreate those low notes your speakers will utilize the bass driver. It will need to be moving quite a bit. The low frequencies it creates will also shake the speaker cabinet.
So, what if you took those low notes away and sent them somewhere else? Like to a subwoofer? Well, as a result, the bass driver, which if you have a small two-way system is also your midrange driver, does not have to move around as much. What you will hear is vastly improved midrange response. Plus, since the speaker cabinet is not shaking as much from the low tones, everything gets clearer too!
If you’re looking for a subwoofer for your home theatre room, you want something that can deliver lots of low-end impact. The biggest thing that can affect this is the size of the room. If you have a large space, you’ll need a large subwoofer, possibly more than one. Multiple subwoofers in a room are a great way to even out the bass response for all the seating positions in your room so that everyone gets that same great experience.
Lots of companies are selling “boomy” subwoofers. They’re loud, but they’re not as tight, as deep, as fast, or as precise as high-quality subwoofers. For the ultimate home theatre experience, you should be able to hear the difference between thunder and an explosion, or the difference between an upright bass and an electric bass.
This all brings us back around to Sealed vs Ported.
Sealed Subwoofers
A sealed subwoofer is a subwoofer in a sealed box. This type of configuration can be put into a relatively small box, making placement in a room easier.
Bass Roll-off
Every speaker has a range of frequencies that it can produce -- some easier than others. When the frequency response drops off noticeable (usually in the lower frequencies), we call that bass roll-off. For example, if the roll-off started at 40Hz you would still have some bass at 30Hz, just not as loud. Sealed subwoofer typically provide a gentler bass roll-off than ported subwoofers.
Consider Timing
Particularly if you are listening to music, timing is also extremely important. You want the low notes that you sent to the subwoofer to sync up as closely as possible to the ones coming from your main speakers. Sealed subwoofers are like most other speakers, the woofer is the only thing producing sound. Lining everything up is a matter of simple tuning.
As you get into larger rooms, think 2,500 cubic feet or more, however, the bass demand increases greatly. One small, sealed subwoofer in a large room is not going to be enough. You’ll need larger and potentially more than one subwoofer to get the same perceived sound you get in a smaller room.
Ported Subwoofers
A ported subwoofer has the woofer and one or more ports, which let the air escape out of the box. This allows you to get a bigger sound out of one box because there are two different mechanisms moving the air -- the woofer and the port.
A ported subwoofer can move a lot of air and fill up a very large room. Because you need the space inside the box for air, ported subwoofers tend to be larger tit for tat with a sealed subwoofer. This is something to keep in mind when deciding where and how you will be placing the subs in the room.
Bass Roll-off
Ported subwoofers roll-off very fast when compared to sealed subwoofers. If you decide to go with a ported sub, you will want one with a large enough woofer to capture all of the low bass tones.
Consider Timing
Timing is can also be an issue with ported subwoofers. Think about the physics. The air moved by the woofer may sync closely with your other speakers, but the air coming from the port is just slightly behind. Ported subwoofers are harder to design properly as you need to tune the port exactly right with the box size and woofer size.
If you can keep that resonance frequency low enough, our ears will not perceive this difference.
Another issue that comes from ported designs is that some people can hear the sound of the air itself escaping from the port. This is known as “chuffing”.
So, What Should I Buy?
Of course, you can have great ported and sealed subs and bad ported and sealed subs. But let’s say you are getting a subwoofer from a highly rated, reputable manufacturer. As with all things in making great sound, it comes down to the room. A large room (above 2500 cubic feet) will probably need either ported subwoofers or large sealed subwoofers, and more than one would be preferable. If your room is smaller than this, one or two great sealed subwoofers will usually be preferable.
If you have some great small speakers and enjoy listening to music as much or more than watching movies, you’ll likely be able to find a sub that can blend with your main speakers better if it is sealed. If on the other hand you love deep, loud bass effects and have a large room, you’ll probably wind up with a ported design.
And just to confuse you, we have on more type of subwoofer to throw into the mix. Some subwoofers are in a sealed box but have what is called a passive radiator to help extend the bass, instead of having a port. The passive radiator is moved by the back wave of air coming from the main woofer. The movement of air from the passive radiator is greater than what would come out of the port. While it’s more of a design challenge to get this right, a system like this can produce great deep bass and keep the cabinet size relatively small. A great subwoofer or two with this type of design can be a wonderful choice for a larger room, where fitting in a big, ported box or two is difficult.
Ultimately the choice is yours. Of course, getting the right subwoofer is only one small battle. Placement, acoustics, tuning the room, and setting up the EQ all play an extremely important role in how everything will sound.