Aspects of the acoustical design and properties of Christchurch Town Hall, New Zealand

The Christchurch Town Hall (2650 seats) is the major hall in a complex which includes a 986 seat theatre. It was opened on 30 September 1972 and was designed primarily as a choral symphony hall. Reverberation time (125 Hz to 2 kHz) in excess of 2·2 seconds with the hall full is provided by a volume of 20 500 m ³ and reflective surfaces. The basic design aim, provision of relatively strong early lateral reflections, is achieved by large interior oblique reflectors which hang free from the boundaries of the reverberant volume. The resulting early lateral energy and long R.T. gives the hall a combination of reverberance, envelopment and clarity. The paper gives an account of design aims and studies including a ray tracing computer program with an interactive graphics output. Measurements of T₆₀, T₁₅ and integrated early energy have been carried out in the hall. Echograms and other measured data are presented. Clarity has been measured by a speech intelligibility test with the Hall empty except for 40 participants. With T₆₀ at 500 Hz 2·7 seconds, the intelligibility was better than the Peutz criterion for public address systems.