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Title page for ETD etd-12062007-131834


Type of Document Dissertation
Author Galster, Jason Alan
Author's Email Address jason@galster.net
URN etd-12062007-131834
Title The Effect of Room Volume on Speech Recognition in Enclosures with Similar Mean Reverberation Time
Degree PhD
Department Hearing and Speech Sciences
Advisory Committee
Advisor Name Title
Todd A. Ricketts Committee Chair
Benjamin W. Hornsby Committee Member
D. Wesley Grantham Committee Member
Kenneth Cunefare Committee Member
Keywords
  • audiology
  • hearing
  • hearing impairment
  • acoustics
  • reverberation
  • room acoustics
  • echo
  • echoes
  • CST
  • STI
  • connected speech test
  • speech transmission index
  • reverberation time
Date of Defense 2007-11-26
Availability unrestricted
Abstract
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.

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