Three Myths about Ported and Sealed Subwoofers
Sealed subs are musical. Ported subs are boomy. This sub is good for music, that sub is good for movies. If you’ve read statements like these, you are not alone. They abound on the internet. They’ve been said so often that people repeat them simply because they’ve heard them so many times they must be true, right? Wrong. This is one of the oldest “old wives’ tales” of AV and we’re here to dispel it. We walk you through three of our favorite myths about ported and sealed subwoofers to expose the truth!
Author’s Note: We are going to make many references to the SVS Sound line of subwoofers. SVS makes sealed and ported subs in the same line that are meant to be equivalent performers. Not a lot of manufacturers do this so we are using them out of ease of discussion. We are huge fans of SVS subs and encourage you to visit their site. They even offer discounts for dual subwoofers!
Subwoofer Design Differences: Ported versus Sealed
At its core, the difference between ported and sealed subs is simply the design of the subwoofers. Ported subs have some sort of port or hole in the enclosure, while the sealed design does not. As the driver moves in and out, the air can move through the port in the ported design while it is trapped within the sealed subwoofer. This basic design difference between ported and sealed subwoofers leads to a number of performance assumptions and myths. Some have a toe in the pool of truth, most do not. Let’s look at them.
Author’s Note: Many of these myths are very old and probably originated from early, poorly designed subwoofer. While we admit that you can create subs that could “prove” these myths, these would be truly terrible subs and unlikely to be mass-marketed.
Myth 1: Sealed Subs are More Musical
This myth comes from how the drivers inside the subwoofers act. More specifically, how the air acts on the drivers. In a ported design, the driver moves in and out and the air moves out and in the port in reaction. There is little air resistance. In the sealed design, the air inside the cabinet has nowhere to go. This means that when the driver pushed out, it creates low-pressure in the cabinet. When it pulls in, it compresses the air creating high pressure. Regardless, the air inside the cabinet is fighting to keep the driver at the midpoint. The thought is that the air acts as a suspension so that the driver can come back to a resting position more quickly than a ported cabinet.
Obviously, the physics of the cabinet and how the air affects the driver can not be disputed. What people forget is that subwoofer manufacturers take all this into account when they design their boxes. With an appropriately powerful amplifier, the driver in the ported box stops just as quickly as the one in the sealed box. In fact, the sealed box usually needs a more powerful amplifier to counteract the air pressures working against the driver!
Myth 2: Ported Subs are “Boomy” or Add Distortion
Because there is air moving in and out of a port, the ported design must be boomy right? They are usually louder than their sealed brethren so clearly they don’t sound as “tight,” right? Wrong. The idea of boomy comes from the assumption that the port somehow adds unwanted bass. Instead, the port is an integral part of the subwoofer design. The designer analyzes the bass coming from the port and tunes the design to maximize how it works with the sound from the driver. While improperly designed ported subs (or ported subs that are being overdriven) can add “port noise,” a well designed ported sub perfectly combines the bass from the driver and port.
Myth 3: Ported Subwoofers have Timing Issues
Again, people look at the port of a ported subwoofer and think, “That’s got to be doing something bad.” It just isn’t true. The thought here is that the air coming out of the port is not coming out at the same time as the air coming from the driver. This means the “timing” of the sound is somehow off. That timing will somehow muddy the bass.
None of that is true. Yes, the air isn’t leaving at the exact same time, but the bass waves are extremely long. A 20hz wave is over 50 feet long! The waves leaving the driver and port are so long they are wrapping all the way around the cabinet. They hit the walls and bounce back before you can even perceive them. The timing difference is not something you’ll be able to hear. The effect of your room on the perceived bass is far more important than any timing issues between the port and the driver.
For more information about subwoofer myths, check out Data-Bass.com.
The Truth Behind the Myths of Ported and Sealed Subwoofers
When looking at the REAL differences between ported and sealed subwoofer, it helps to look at actual subs. SVS has lines of subs with a sealed box, a ported box, and a ported cylinder options. The two ported designs measure the exact same, the only difference being the shape of the subwoofer. But let’s look at the differences in the measurements between the ported and sealed offerings:
Here we are looking at the SVS 2000 Pro like of subwoofers. The yellow line is the SB-2000 Pro (sealed sub) and the purple is the PB-2000 Pro (ported sub). The differences in the seal versus the ported subwoofers are pretty obvious if you are used to reading these graphs. If you are not, let us walk you through it.
REAL Difference 1: Ported Subs can Play Louder at Low Frequencies
First, you’ll notice that through most of the frequency range (in this case, from 10Hz to 300Hz), the two lines are parallel. The yellow line is consistently below the purple one. This reveals one of the “truths” about the differences between ported and sealed subwoofers: Ported subs can be louder.
But it is not for the reason you think. That purple line is above the yellow, but the SVS Pro line uses the same amp in both subwoofers. Had they used a larger amplifier in the sealed sub, they could have pushed that yellow line farther up. Where we get the “louder” from is actually the left side of the graph. Here we see the yellow line start to drop off before the purple. The ported sub stays flat up to 20Hz and maybe a little past. The yellow starts to lose output at these lowest frequencies.
This is likely one of the reasons for the “boomy” myth. Ported subwoofers, all things being equal, will play lower than a sealed sub. If you are looking for pure extension, a ported sub is the way to go.
REAL Difference 2: Sealed Subs Lose Output Slower than Ported
On the other hand, look at how quickly the output drops off on the left side. The yellow line of the sealed subwoofer has a gradual dropoff while the purple drops like a stone. This is a limitation of the design. Ported subs just hit the limit of their extension and lose output. Sealed drop off more gradually. Theoretically, you could EQ the sealed sub to increase the output at these low frequencies, but that takes a lot of amplifier power and you risk adding distortion to your sound.
Which Sub is for You?
We’ve already written about how to shop for a subwoofer. The key thing to remember is that you need to match the subwoofer to your room. The rule of thumb with subs is that you can get low, small, or cheap – pick two. To get that small sub that has a lot of low-end output, you’ll have to spend big bucks. To get an affordable sub with a lot of low-end output, be prepared to deal with a very large box. If you only have space for a small sub and you don’t have a lot of money, don’t expect a lot of low-end extension.
Port or no, a good sub is a good sub. There are no subs that are good for music but not movies (or vice versa). Stop worrying about a port and start worrying whether or not the sub can fill your room with sound. Don’t believe the myths about ported and sealed subwoofers! Sealed or ported, a sub that is properly matched to your room will sound fantastic for both music and movies.
Ready to shop for a subwoofer? Make sure you are buying the right sub for your room with our Subwoofer Buying Guide!