Axial Mode

An axial mode is a room resonance that occurs between two parallel surfaces, involving only one dimension of the room. It is the strongest type of room mode because sound bounces directly between two opposing surfaces with minimal spreading. The first axial mode between two walls separated by distance L occurs at f = c/2L. For a room 5 m long, this is approximately 34 Hz. Higher-order axial modes occur at integer multiples of this fundamental frequency. Axial modes dominate the low-frequency behavior of small to medium rooms and are the primary cause of bass coloration in untreated spaces. They produce pressure maxima at the boundaries and velocity maxima at the room center. Broadband bass absorbers placed in corners are the most effective treatment because all axial modes have pressure maxima at room boundaries.