Noise enclosures are used to control the noise radiated by industrial machines such as pumps and internal combustion engines. The passive transmission loss of enclosures at low frequency can yield negative insertion loss occurring at resonances of the enclosure panels backed by the internal air cavity. Active noise control provides a means to enhance low frequency performance by eliminating enclosure resonances. The proper design of a noise enclosure will account for operator and maintenance access, ventilation, safety codes, and possible needs for future expansion. The acoustic design of a noise enclosure is driven by the decibel reduction required to meet goals.