The Effect of Room Volume on Speech Recognition in Enclosures with Similar Mean Reverberation Time

• Main Author: Galster, Jason Alan
• Other Authors: Todd A. Ricketts
• Format: Others
• Language: en
• Published: VANDERBILT 2007
• Subjects: Hearing and Speech Sciences
• Online Access: http://etd.library.vanderbilt.edu/available/etd-12062007-131834/

This project investigated speech recognition in rooms of different size with similar average reverberation times. A comparative analysis of existing literature has provided evidence to support that speech recognition in small rooms may be poorer than in larger rooms when the two spaces have a similar amount of reverberation. This study evaluated speech recognition using sentences binaurally recorded using an acoustic manikin in three rooms of different volume and/or dimension. The three rooms included a small reverberation chamber (48 m3), a university lecture hall (479 m3), and a high school band practice room (474 m3). Speech recognition was tested using bilateral insert earphones in two groups with 13 participants in each group. One group consisted of individuals with normal-hearing and the second group consisted of participants with mild-to-severe hearing impairment. Testing was completed at five signal-to-noise ratios (SNRs) for each group. Several measures, designed to quantify the acoustic characteristics of each room, were made and included mean free path, frequency-specific reverberation time and the Speech Transmission Index (STI). This investigation determined that listeners in both groups showed a significant decrease in speech recognition performance as SNRs decreased and a significant effect of room size. The poorest speech recognition was measured in the smallest room. There was no interaction between SNR and room type for either of the two participant groups. The effect of both change in room size and SNR correlated well with changes in Speech Transmission Index. A rationale was proposed as the source of the room size-specific reverberation effects. This idea speculates that the period during which early reflections are beneficial to speech understanding may decrease as room size increases. This is consistent with measures of decreased mean free path in smaller rooms. In addition, the reverberant field of a small room will contain more reflections than a larger room when the two are matched for reverberation time. It is proposed that the increased number of overlapping reflections also contributes to decreases in speech recognition ability.