August 11, 2016
When purchasing a bass cabinet, there are many factors to consider, such as speaker configuration, size, weight, power handling, portability, and of course, how it sounds. However, a somewhat overlooked component of a speaker enclosure’s overall sound is whether it is sealed or ported. Both cabinet formats have their own benefits and drawbacks, and this article will cover the basic differences and help you determine which one will be the optimal choice for your bass amp setup.
Sealed Bass Cabinets
Sealed bass cabinets are exactly what their name implies- the enclosure is sealed, making it so that no air can escape. This means that all the sound comes from the front of the speakers themselves. The trapped air inside the cabinet acts as a spring controlling the movement of the speaker resulting in a tighter, punchier, and more responsive and articulate sound. The low end of the speaker is rolled off slower, so it may sound a little more rolled off on the low end than a ported cabinet. Note this is determined by the box size and the speaker used, so sealed does not always mean less low end. Another over looked feature of this type of cabinet is that the internal air holds the speaker from over movement at very low frequencies like an internal limiter. If the cabinet is ported, very low frequencies below the port tuning will release the internal air’s hold on the speaker and it could damage the speaker at much lower wattage than the speaker’s handling wattage.
These cabinets are convenient in that they can be more compact and possibly lighter weight than ported cabinets. However, they may be less efficient at low frequencies, therefore they may require a more powerful amplifier, but because they are sealed they usually can take the extra power at lower frequencies. Another advantage is they usually always sound the same wherever they are placed in the room, unlike a rear ported cabinet that changes with its distance from the wall behind it.
This Carvin Audio BR210 is a sealed cabinet.
Ported Bass Cabinets
Ported cabinets, also known as bass reflex cabinets, have ports either in the front or rear. These are used to tune the enclosure to a certain low frequency based on the speaker being used.
More technically, a this type of cabinet design tunes the cabinet to a resonant frequency that works with the speaker to create more output at low frequencies up to the roll off point. This is done by sharpening the low end roll off which peaks up the low frequencies to this roll off point. The port puts out these lower frequencies like another speaker resonating in the cabinet. This lets more air movement and thus the speaker moves more at these low frequencies making the cabinet provide an extended bass response that the same sealed cabinet would not be able to produce at the same power level. As such, these cabinets can sound louder at low bass frequencies.
While big, rumbly bass may be awesome, the transient response of this low bass in this type of cabinet may not be as good as its sealed counterpart. Going back to the spring analogy, the spring in a sealed cabinet is always connected with a fast recoil due to the trapped internal air. In a ported cabinet the spring will release the speaker if the frequency goes below the port tuning due to the air escaping, because the speaker can’t pull it back. A poorly designed port with a “tubby” low end may provide an overwhelming amount of bass that is difficult to tame in certain rooms. In addition, ported enclosures may be larger than sealed enclosures due to the extra cabinet area needed to accommodate the port.
Note as stated a few times, if you go below the ported cabinet’s designed low frequency, the port will unload the speaker, meaning it will not control or hold the speaker any more, which can result in the speaker moving beyond its capability. This can result not only in no sound for a moment, but in damage to the speaker. In some instances of this you can actually hear the voice coil of the speaker hit the back of the magnet plate. This is certain to cause permanent damage.
The Carvin Audio BR115, a ported cabinet.
Choosing the Right Cabinet
The debate of sealed vs. ported is very common in the bass guitar world. The selected speaker enclosure type can have an effect on the type of bass response the speaker will have, but a well designed cabinet that is either sealed or ported for a specific purpose should not be as much of a difference as some may think. And with bass cabinets, a huge part of the overall tone comes from the interaction between the speaker cabinet and your surroundings. If you are making the decision between these two types, keep in mind these basic differences but also remember that no two ported or sealed cabinets will sound the same, and there may be enclosures that sound uncharacteristic- for example, you may find a ported cabinet that sounds punchier than a sealed cabinet! Also note that changing the speakers used may drastically change the sound capability of either type cabinet tuned to the original speakers. Be sure to try as many cabinets as you can while using your amplifier head.
Which cab type are you currently using in your setup? Let us know in the comments!
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