In the previous section, we learned a bit about the different kinds of materials and construction techniques for making a quality speaker box/cabinet, but what kinds of cabinets are there really? Remember, when designing a speaker cabinet you must take the characteristics of the driver you are using into account.

Sealed
A sealed cabinet is basically a box with the driver in one (or more) sides. The air inside the cabinet cannot escape, and so the driver does have to overcome the force of the air as well as its own suspension. This gives a sealed cabinet good dampening properties, but not very good extension as the lower notes require more force than the speaker is able to overcome against the force of air. While the sealed cabinet does have higher sound quality due to the damping characteristics of the air behind the driver, it is also one of the easiest cab designs to produce unwanted standing waves between the different walls of the cab, but this can be overcome through various means, including foam lining, cabinet stuffing, or even internal baffles.

Ported
A ported box is one large helmholtz resonator. To visualize this, imagine a metal ball. If you push the ball on a flat surface, the ball will roll until it hits something. Now imagine a single pipe with air flowing through it. Though the air doesn't have as much momentum as a metal ball, the air in the tube does keep moving in a similar way. if you suddenly attach a spring to the ball, when you push it away from the spring it will keep going until the spring pulls it back, the comes closer until the spring pushes it away. In a similar way that the driver had to push against the air in a sealed cabinet, the momentum of air in the tube pushes against the air in the cab like a spring, resonating back and forth producing sound waves. When a speaker is placed in a box like this, the speaker becomes coupled to the tube and box, and can cause some notes to form through the tube, like blowing across a bottle top. The best part of this cabinet is that it can give much lower extension than a sealed cabinet can due to its resonant properties. But because of that resonance, distortion is introduced, just like a standing wave would be introduced inside of a sealed cabinet. Because of its better extension, ported cabinets are often used for subwoofers and mid/woofers.


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