A type of speaker enclosure that is completely sealed with no port or other device to let air inside the enclosure flow outside the enclosure. Most speakers’ midrange drivers and tweeters are acoustic suspension units as are many woofers and subwoofers.

The acoustic suspension enclosure, a sealed enclosure, is different from a ported design in that a ported design uses a tube opening to the outside (outside the box) to extend bass output by 2 to 3 dB. An acoustic suspension design is less efficient than a ported design and must use additional amplifier power to achieve the same sound pressure as an otherwise equivalent ported box. However, the acoustic suspension design is able to play lower in the frequency spectrum and provides an arguably tight and more defined sound. The acoustic suspension enclosure is also the easiest to make with the most important (indeed vital) consideration being the size of the box (the box size must meet strict guidelines in order to work properly with a given bass driver putting out the most sound for a given input without sounding bloated).

An acoustic suspension design takes advantage of the sealed enclosure to act as a spring helping to move the bass driver. As the driver moves in, the air inside the box is compressed. As the driver moves out, this compressed air acts like a shock absorber pushing the driver outward. This constant compression and decompression within the sealed enclosure helps this type of speaker enclosure to attain the lowest frequency response (all things being equal). However, it is important that such a design be absolutely sealed so that no air escapes or enters the box. Many high-end subwoofer systems use acoustic suspension designs.