A room can be compared to a loudspeaker enclosure. Both the room and the enclosure are surrounded by six surfaces. The differences between the two lie in their size and composition. Yet the similarity in construction is great enough to warrant a comparison.
Loudspeakers fall into two general categories. First the resonant enclosure, Fig. 6.2 (a), such as the bass-reflex type, with the characteristic resonance determined by the enclosure's size and the port in the baffle. Then there is the non-resonant type, Fig. 6.2 (b) which employs the largest possible horn mouth to minimise any possible resonant condition.
Fig. 6.2 Two general categories of loudspeaker (a) The resonant type (b) The non-resonant type