Resonance

The tendency of a vibrating or oscillating system to vibrate or oscillate at certain frequencies more easily than at other frequencies. In a speaker or subwoofer, the enclosure tends to reinforce certain frequencies whose wavelengths are related to the enclosure’s dimensions and internal shape. Also, each speaker driver can exhibit resonances at certain frequencies.

The goal of speaker and subwoofer design is to minimize resonances so the overall frequency response is even throughout the operational frequency range.