Negative Effect of Acoustic Panels on Listening Effort in a Classroom Environment.

Abstract

Acoustic panels are used to lessen the pervasive effects of noise and reverberation on speech understanding in a classroom environment. These panels, however, predominately absorb high-frequency energy important to speech understanding. Therefore, a classroom environment treated with acoustic panels might negatively influence the transmission of the target signal, resulting in an increase in listening effort exerted by the listener. Acoustic panels were installed in a public school environment that did not meet the ANSI-recommended guidelines for classroom design. We assessed the modifications to the acoustic climate by quantifying the effect of (1) acoustic panel (i.e., without, with) on the transmission of a standardized target signal at different seat positions (i.e., A-D) using the Speech Transmission Index (STI) and (2) acoustic panel and seat position on listening-effort performance in a group of third-grade students having normal-hearing sensitivity using a dual-task paradigm. STI measurements are described qualitatively. We used a repeated-measures randomized design to assess listening-effort performance of monosyllabic words in a primary task and digit recall in a secondary task for the independent variables of acoustic panel and seat position. Twenty-seven, third-grade students (12 males, 15 females), ranging in age from 8.3 to 9.4 yr (mean = 8.7 yr, standard deviation = 0.7), participated in this study. Qualitatively, we performed STI measurements under both testing conditions (i.e., panel and seat location). For the primary task of the dual-task paradigm, participants heard a ten-item list of monosyllabic words (i.e., ten words per list) recorded through a manikin in the classroom environment without and with acoustic panels and at different seat positions. Participants were asked to repeat each word exactly as it was heard. During the secondary task, participants were shown a single, random string of five digits before the presentation of the monosyllabic words. After each list in the primary task was completed, participants were asked to recall the string of five digits verbatim. Word-recognition and digit-recall performance decreased with the presence of acoustic panels and as the distance from the target signal to a given seat location increased. The results were validated using the STI, as indicated by a decrease in the transmission of the target signal in the presence of acoustic panel and as the distance to a given seat location increased. The inclusion of acoustic panels reduced the negative effects of noise and reverberation in a classroom environment, resulting in an acoustic climate that complied with the ANSI-recommended guidelines for classroom design. Results, however, revealed that participants required an increased amount of mental effort when the classroom was modified with acoustic treatment compared to no acoustic treatment. Independent of acoustic treatment, mental effort was greatest at seat locations beyond the critical distance (CD). With the addition of acoustic panels, mental effort was found to increase significantly at seat locations beyond the CD compared to the unmodified room condition. Overall, results indicate that increasing the distance between the teacher and child has a detrimental impact on mental effort and, ultimately, academic performance.