Précis of the TC-25CSS Theater Testing Report

Abstract

In 2014, SMPTE’s B-Chain Study Group Theater Testing Data Report Group released a major report about the acoustical performance of sound systems in four cinemas and two dubbing stages. This paper provides a precis of this B-Chain report, which is probably the most comprehensive in-depth analysis of cinema audio spaces that has ever been undertaken. The report presents numerous frequency and temporal responses for these sound systems, with in depth analysis of the center channel systems. Being based on the measured impulse responses of the systems, the report’s measurement process departed from current SMPTE standardized methods, which are “time blind.” As such, considerable insights have been gained into the behavior of these systems and the way in which frequency responses develop over time. Of particular interest is the minimal contribution that the reverberant sound field makes to the high-frequency responses. The measured responses indicate significant disparity among venues in the responses at low and high frequencies. One of the report’s conclusions is that the commonly-accepted acoustic mechanism for the roll off of high frequencies known as the X curve does not occur. Discussion of the report’s key features such as the analysis methods, trends in the responses, and conclusions is provided in the paper.