There are different types of speaker box designs such as ported, sealed or bandpass enclosures. In addition to these designs, some people prefer custom speaker box designs to fit custom enclosures. The design depends primarily on the environment where the speaker box will eventually be situated.
Sealed speaker boxes are speaker enclosures that do not have any holes or ports on the box. The speaker can be touched directly without obstruction (unlike with a bandpass box). Sealed speaker boxes lock the air inside the box. With the speaker pumps creating sound, the pump reverberates the box and the air inside. Since the air and sound have nowhere to escape, they are both trapped inside the box, magnifying the sound. The resulting sound is louder but not necessarily cleaner. The sound is dirtier because the original "kick" is amplified and delayed slightly by the reverberating box. Sealed boxes are commonly found with subwoofer enclosures in car audio installations. Since most car audio subwoofer enclosures are found in the trunk of cars, the distorted bass is not an issue.
Ported speaker box designs produce a cleaner, "tighter" bass and are used in home audio more than car audio. Ported speaker box designs have holes or ports in the box to allow air to pass in and out of the box. This allows the air from the pumping speaker a chance to escape the enclosure. As a result, the sound is tighter, since there is no reverberation or air and sound in the box. Ported speaker box designs typically are not as loud as other designs but produce the highest quality sound, which is why they are most often used in home theater setups.
Bandpass speaker box enclosures are almost exclusively found in car audio installations. Bandpass enclosures have another speaker box covering the outer portion of the speaker. This outer enclosure is usually a strong Plexiglas. The second enclosure acts like another sealed speaker box and amplifies the sound produced by the woofer. It can be thought of as two speaker boxes for one speaker. The resulting sound is significantly louder than a ported box. However, because the face of the speaker is enclosed in a second box, the sound is muffled and slightly distorted. This is why this design is used for subwoofers in car audio.
