Room Modes With Regard to Speech Intelligibility in Classrooms: Response to Shalkouhi (2010)

Purpose: To respond to comments by Shalkouhi (2010) on the article "Background Noise Levels and Reverberation Times in Unoccupied Classrooms: Predictions and Measurements" by Knecht, Nelson, Whitelaw, and Feth (2002). Method: The Schroeder frequencies calculated by Shalkouhi (2010) were compared with the octave-band weighting factors used by Steeneken and Houtgast (1980) in their calculation of the Speech Transmission Index. Results: To assess the potential impact of invalid reverberation times measured at 125 Hz on speech understanding in the classrooms, we note that the weight given to the octave band at 125 Hz is 0.0. Conclusions: Since the octave band of background noise centered on 125 Hz has no impact on speech understanding, we suggest that reverberation time measures at 125 Hz are unnecessary. Key Words: classroom acoustics, reverberation time, speech transmission index, Schroeder frequencies