Doctoral Dissertations

Date of Award

8-1989

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Speech and Hearing Science

Major Professor

Anna K. Nabelek, Carl W. Asp

Committee Members

Igor Nabek, Kathleen Warden

Abstract

Loudspeaker-to-listener distance was assessed for consonant and vowel identification scores of 12 adults with normal-hearing and 12 adults with high frequency hearing loss in a 415 ml (i.e., 18 m x 7.2 m x 3.2 m) lecture hall, with a 1.5 s reverberation time, and a 3.3 m critical distance. Outside the critical distance of the lecture hall, the contribution of direct speech energy was negligible as the sound was primarily composed of reflected energy. Each listener was seated at two distances within the critical distance (i.e., 1 and 2 m) and three distances outside the critical distance (i.e., 4, 8, and 15 m) at a zero degree azimuth to the separation between two loudspeakers placed side-by-side. One loudspeaker presented consonant-vowel-consonant-vowel (i.e., CVCV) items from a nonsense syllable test, at 77 dB-A at 1 m. The 24 listeners were tested at all five distances in two speech-to-noise ratio (i.e., S/N) conditions. These were: (1) varied S/N in which the speech level decreased with distance in relation to a 45 dB-A ambient noise level, resulting in a +32 dB S/N at 1 m to a +23 dB S/N at 15 m, and (2) fixed S/N in which a multi-talker babble was presented through the other loudspeaker and adjusted to maintain a +15 dB S/N at all five distances. All 12 hearing-impaired adults were tested IV without a hearing aid. Only 42% (i.e., 5 of 12) of the hearing-impaired listeners wore hearing aids in their personal lives.

Vowel and consonant scores of the normal-hearing adults were significantly better than of the adults with high frequency hearing loss. Consonant scores were higher within the critical distance than outside the critical distance, with no decrease in performance as distance increased in the reverberant field. Vowel scores were unaffected by distance except in the extreme conditions, with scores at 1 m being significantly better than at 15 m. Both consonant and vowel scores were significantly better in the varied than the fixed S/N condition. For both consonant and vowel scores, the Groups x Distances and S/N Conditions x Distances interactions were not significant suggesting similar trends in performance for these conditions. The results of this study suggested that unless a listener moves to within the critical distance of a speech source, decreasing loudspeaker-to-listener distance from one point to another in the reverberant field may not improve aural phoneme identification.

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