Code of practice for the acoustic design of auditoriums and conference halls
1963 Edition

IS 2526 specifies reverberation times at 500 Hz that vary based on the hall's purpose and size. Speech-focused halls require shorter reverberation times, typically between 0.6 to 0.8 seconds for a 1000 cubic meter volume, to maintain clarity. Music venues benefit from longer reverberation times, about 1.2 to 1.6 seconds, to enrich sound. School auditoriums and theatres fall in an intermediate range, around 0.8 to 1.0 seconds. These values increase with room volume and are detailed in the standard's graphical data.

According to IS 2526, seats should be arranged in concentric circular arcs centered behind the curtain line, positioned at a distance equal to that from the curtain line to the rear wall, enhancing both visibility and sound distribution. Staggering seats laterally prevents direct obstruction by those seated ahead, improving sightlines and acoustic clarity. Acoustic design must also include minimizing external noise and HVAC disturbances to ensure clear sound at every seat.

The standard recommends various sound-absorbing materials such as acoustic plaster with insulation granules, perforated or unperforated compressed cane or wood fibreboards, wood particle boards, mineral and glass wool quilts, mats, and tiles, as well as composite units combining perforated hardboard with fiberboard. These absorptive materials should be strategically applied to areas like rear walls, balcony parapets, concave surfaces, and other reflective zones to prevent echoes, sound focusing, and excessive reverberation, ensuring uniform sound quality throughout the space.

Sound amplification becomes necessary when the audience size exceeds 600, background noise levels surpass 45 to 50 dB, or when the hall volume is above 1400 cubic meters or speaker-to-listener distances exceed approximately 23 meters. Amplification systems should provide an average sound pressure level up to 80 dB across the seating area. The design should aim to maintain even sound coverage and minimize echo or reverberation, preferably using low-level loudspeakers or individual headphones to enhance listener comfort.

IS 2526 emphasizes selecting quiet locations for open-air auditoriums, ideally where ambient noise levels are below 45 dB(A) and wind speeds are under 16 km/h to prevent sound distortion. Site planning should include noise surveys and proper orientation to minimize noise intrusion. Mechanical noise from air conditioning or equipment must be isolated effectively. Speech loudness targets are typically 60 to 70 dB, with amplification used if ambient noise or size conditions exceed acceptable limits, ensuring clear audio performance despite the open environment.