Sealed or ported subwoofer enclosures - Which is Better?

Sealed or ported subwoofer enclosures… this debate will never be settled because the answer is subjective. The type of music you listen to, the specifications of the subwoofer(s) you choose, the available space to install your subwoofer enclosure, and other contributing factors all play a role in determining whether a sealed or ported (vented) subwoofer enclosure is better. The real answer to this long debated question varies depending on factors like these in each application.

MTX already knows that the only way you're going to get full, rich bass from your car stereo system is to add a subwoofer. The addition of a subwoofer to your system will greatly improve the fun and impact of your music, no matter what kind of music you listen to. When considering what style of enclosure to buy or build for your subwoofers, you have to answer some questions that will lead you to the right answer for your specific listening preferences and vehicle.

Ported/vented subwoofer enclosures

If you like your music “boomy”, vibrating your car’s body panels, you want to consider a ported (vented) enclosure. These types of enclosures, when built with the properly calculated volume and tuned to the correct frequency for the subwoofer, are generally louder than a sealed enclosure. In a vented enclosure the woofer and port work together with the port resonating like a pipe organ. This works with the woofer to generate more bass than a sealed box.

Ported enclosures are generally larger in overall size, so some installations may not have enough available space for a ported enclosure built to the proper specifications. Tuning of the port is critical to maximizing the output capability of the subwoofer. They allow subwoofers to reproduce the lower frequencies found most often in rap and hip hop music.

Tuning the port is a science and is done through calculations including the size and length of the port among other things. But if a port is not tuned correctly, it can limit the performance of your subwoofer(s) and/or have a damaging effect that may eventually cause your sub to fail. MTX Audio subwoofers are designed with built-in protection to reduce the possibility of failure if installed in a vented enclosure that is not tuned properly, but improper tuning will still cause unnecessary stress, and will hinder performance.

Ports/vents can be round, square, triangular, rectangular or any custom shape you can think of. For example, the port of the enclosure shown above is a rectangular slot port in the front of the enclosure. The port/vent shown below is triangular in shape and is also a slot port design but is located on the side of the enclosure.

You typically find ported enclosures in vehicles that compete in SPL (sound pressure level) competitions which measure how loud a vehicle’s sound system is in decibels or dB’s.

Ported enclosures are generally more efficient in regard to the amplifier power necessary to make the subwoofers perform and allow you to use a smaller amplifier than you would need with a comparable sealed enclosure. Another advantage of choosing a ported enclosure is that the air flowing in and out of the port help to keep the subwoofer cooler. Subwoofers in a ported enclosure are a bit more reliable and will last longer than they would in a sealed box simply because they run cooler.

Sealed subwoofers enclosures

Some people prefer sound quality over SPL, or “tight”, more accurate bass over rattling the mirrors of their car. Sealed enclosures aren’t typically as loud as ported enclosures but they still enhance the listening experience greatly by providing more defined low frequency passages such as kick drums. The bass can still be felt in your chest and in the seats of the vehicle as if you were front row at a concert.

Sealed enclosures reproduce the low frequencies more accurately than ported enclosures because the air inside the box acts like a shock absorber, allowing the subwoofer to move back and forth in more control. The sound waves are reproduced more accurately than with a ported enclosure but the subwoofers may require slightly more power from the amplifier to get the woofers to move as much as they would in a ported enclosure. Sealed enclosures are generally smaller and easier to build because there is no port to tune. You simply build the enclosure to the proper specification for your chosen subwoofer(s).

Conclusion

So whether you listen to rap, country, metal, or classical, your sound system can be improved with the addition of a subwoofer. How much space you have available, or are willing to give up, to install a subwoofer can be the deciding factor as to whether you choose a ported or sealed enclosure. But with either choice, build the enclosure to the appropriate specification given by the subwoofer manufacturer. The best subwoofer on the market can and will perform like a $10 flea market model if the enclosure isn’t built properly.

Specifications and definitions to consider

When researching enclosures and subwoofers, below are some of the more important specifications and terms you will need to know in order to make the right decision as to whether a subwoofer and enclosure combination is appropriate for each other.

Driver displacement – Driver displacement is the volume of space displaced inside the enclosure after the subwoofer(s) has been installed. The enclosure volume before the subwoofers are installed minus the driver displacement of each subwoofer will give you a final volume for your enclosure which should be as close to manufacturer spec as possible.

Frequency response – the frequency range that a subwoofer can reproduce under normal circumstances denoted in hertz (Hz).

Recommended enclosure volume – The amount of volume inside the subwoofer enclosure that the manufacturer of a subwoofer recommends (after the subwoofers have been installed) in order for the subwoofer(s) to perform to their maximum potential.

Subwoofer mounting depth – the amount of depth from the bottom of the mounting flange to the back of the subwoofer. You must ensure that your enclosure depth is slightly greater than the mounting depth of your subwoofer in order to make sure there can be a good seal between the mounting flange and the enclosure.

Bottom and top depth – If you find this spec, you are probably looking at a wedge style enclosure. Not all enclosures are a perfect square or rectangle. Some enclosures are wider at the bottom than they are at the top creating an angle that is usually meant to match closely to the angle of a rear seat so the enclosure fits nicely up against the back of the seat inside a trunk.

What does subwoofer phase mean?

Have you ever heard people say their speakers or subwoofers are in phase or out of phase? If so, do you really know what that means? In phase must be correct and out of phase must be wrong… Right? Not necessarily.

Each speaker has a positive (+) and negative (-) terminal. If you were to wire the positive (+) speaker terminal to the wire connected to the negative terminal of the amplifier and the negative (-) speaker terminal to the positive (+) terminal of the amplifier, you would have wired your speaker “Out of phase.”

When there are two woofers in the same enclosure with both woofers facing the same direction and one is wired out of phase, the woofer wired out of phase will move the opposite way. Within the subwoofer box, this can cause damage at high power levels because the woofers are moving in different directions and the pressure inside the enclosure can allow the subwoofers to move too much and/or too little. Too much movement can cause the subwoofer to move outside of linearity and too little movement can prevent the coils from cooling off.

Connecting wires from the positive (+) terminal of the speaker to the positive (+) terminal of the amplifier, and connecting the speaker negative (-) to the amplifier negative (-), is called “wiring in phase" and is the more common type of wiring.

Why would you ever want to wire your speakers or subwoofers “out of phase?” Well, have you ever seen installations where one or more subwoofers are mounted inverted to the listener? This means the back of the subwoofer is mounted outward. It is necessary to wire the inverted woofer “out of phase” in order to make it reproduce the audio signal in sync with the non-inverted subs.

In the out-of-phase diagram above, the two subwoofers on the left and right are mounted inverted and would require wiring to be “out of phase” in order to perform correctly.

To understand what is happening, remember that the audio signal is an analog AC (alternating current) signal. So when the positive signal goes to the speaker, it pushes the subwoofer forward. When the signal sent is negative, the subwoofer pulls backward.

When two woofers are mounted in the same enclosure and one woofer is inverted, you would need to wire it “out of phase” in order to make the sub perform correctly. When the woofers are pointing in different directions, and one is out of phase, the cones will then move together and not cancel out. This arrangement works well if you would like to have the rear side of a subwoofer showing in your installation.

This is how phasing of speakers is done intentionally. But what if you accidentally wire your speakers or subwoofers wrong? Or what if you speaker wires and/or terminals aren’t easily identified as positive or negative? How do you know if your speakers and subwoofers are wired correctly?

How do you know?

The most common symptom of a speaker or subwoofer that is wired “out of phase” (when it shouldn’t be) is loss of bass. If you experience this, there are a couple ways to test the wiring phase.

1. Listen to the audio – Turn the bass to the highest setting and turn the volume to a moderate level, adjust the balance and fade to one particular speaker. Listen to the bass, then change the balance to the opposite speaker. If your speakers are out of phase, you will notice more bass response from one speaker than the other.

2. Test your speakers - If you have access to the speakers, connect a 12v or 14.4v drill battery, flash light battery, etc… to the speaker terminals, the speaker cone will jump forward (away from the magnet) or backward (toward the magnet) on the speaker. When the speaker cone jumps forward (away from the magnet), recognize which terminal is attached to the (+) positive side of the battery, this is the (+) positive terminal of the speaker.

If you wire your speakers or subwoofers and there seems to be a substantial lack of bass, be sure to check your wiring. It could be as simple as switching the wires. Wiring “out of phase” does nOT cause any damage to full range speakers or the amplifier, but subwoofers can be damaged if not wired properly and the problem is not identified soon after installation.

Wiring subwoofers “out of phase” in the wrong application can cause the signal to pull against each wind of the voice coil which will heat up instantly and burn or short out causing the woofer to fail.

Out of phase voice coils on a dual voice coil subwoofer

If the coils are wired out of phase on a dual voice coil subwoofer, damage can occur when signal from a amp is applied. The subwoofer will have no output, and will not be moving. This occurs because the subwoofer has no output in that each voice coil is pushing against the other coil. This condition won’t allow the subwoofer to move or make any sound. At the same time a tremendous amount of heat will be generated because the coil is not moving to cause air to rush by it. If a large amount of power is applied to the subwoofer in this case it will “cook” the coil which can cause premature failure. It’s like trying to ride a bike up a hill by pushing down on both petals at the same time. You won’t get anywhere except hot and sweaty.

In phase voice coils on a dual voice coil subwoofer

When the coils are wired in phase they both work together to move the subwoofer up and down according to the signal from the amplifier creating the bass that one would desire.