Completed while Ritchie was Composer-in-Residence with the Dunedin Sinfonia in 1993, Boum is named after a mysterious echo heard by characters in E.M. Forster's novel A Passage to India. The echo comes to symbolise the mysteries of life and death, and was a starting point to a general theme of existentialism and human struggle that pervades Ritchie's symphony.

An eclectic range of influences can be heard across Boum's four movements. A languid, Eastern-sounding violin theme in the first movement is influenced by gamelan music, referencing the pelog scale. Inspired by traditional music of the Cook Islands, the jaunty second movement is a vigorous scherzo dominated by the sound of log-drum and tom-toms. The third movement is a lament for the victims of the Bosnian war, its evocative opening inspired by the wailing of a Maori karanga, while the fourth movement can be thought of as a symphonic dance, its pulse and motivic ideas reminiscent of rock music.