Abstract
This paper evaluates $C_{50}$ in elementary school classrooms and considers utilization of $C_{50}$ as an assessment indicator of acoustic performance. $C_{50}$ is early-to-late arriving sound ratio, recent study reported that $C_{50}$ is more appropriate as a measure of clarity and speech intelligibility than D50 because it is linearly related to subjective responses. The average of $C_{50}$ in elementary school classrooms appeared to be about +2 dB ~ +3 dB throughout 500 Hz ~ 4 kHz. However, absolute evaluation is difficult because there is no suitable reference or standard yet. As deviation of $C_{50}$ according to location is larger than reverberation time, it is expected that $C_{50}$ will be more sensitive when someone assesses acoustic performance of classrooms. Correlation between $C_{50}$ and reverberation time is very high. From logarithmic regression equation, we can estimate appropriate range of $C_{50}$ in elementary school classrooms indirectly, using standard of reverberation time in ANSI.