The effect of seats on the calibration of cinema sound systems

Standardized loudspeaker calibration is necessary for consistent reproduction across cinemas. Generalized corrections are often made to loudspeaker outputs; however, these may be affected by the seats themselves – the ‘seat dip effect’. This paper aims to assess the impact of seats on the current calibration methods used in cinemas, to determine whether changing microphone height improves the frequency response and perceived sound quality in the calibration seat. A measurement microphone and dummy head were respectively used to assess the sound field and obtain listener preferences in three different venues. Seat dips are noted for all three venues, with decreasing attenuation with height above the seat at frequencies within the expected range . Other modal effects are found: these are attributed in part to room geometry and reflective-boundary boosts. The subjective experiment shows that listeners could identify a difference between calibrations made at different heights, but did not prefer a ‘correctly-calibrated’ sound field over an incorrectly calibrated one. It is concluded that current calibration methods do not successfully account for disturbances caused by room geometry and seating and the effect of these on the direct sound and early reflections.