[A study on speech intelligibility in traffic noise]

In studying speech intelligibility in traffic noise, I was able to reproduce a sound field with considerable reality by reproducing both speech and traffic noises by the speaker method using a CD. As a result, the following conclusions were reached. 1) The influence of noise on speech intelligibility is similar for the single syllable and adult disyllable in normal persons. 2) The influence of the kinds of noises and changes with time in the sound pressure level on the intelligibility of the single syllable does not easily manifest itself in patients with sensorineural hearing loss. 3) The speech intelligibility depends largely on the blocking effect of the mid-high frequency components of the noise in both normal persons and patients with sensorineural hearing loss. 4) The intelligibility of the second sound of the adult disyllable is good in both normal persons and patients with sensorineural hearing loss. Furthermore, normal persons can understand a significant disyllable word to some extent by means of "uncertain understanding" even when they cannot hear each vowel and consonant clearly. 5) The intelligibility of the vowel is good in both normal persons and patients with sensorineural hearing loss. 6) As for the intelligibility classified by consonant in normal persons, the intelligibility of the nasal sounds (m, n) and voiced consonants (b, d, g, r, z) becomes low in the case of the S/N ratio being poor. 7) In patients with sensorineural hearing loss, the intelligibility of the bulldozer noise was the lowest, followed by motorway noise among the noises applied. The frequency spectrum distribution of the former consisted mainly of mid-high frequencies of 1 kHz or more. A serrated change with an amplitude of about 6 dB, 2 Hz was noted at the sound pressure level. A sine wave-like change with an amplitude of about 7 dB, 1 Hz was recognized at the sound pressure level of the latter. These are considered to be factors which account for a decline in intelligibility. The present study is part of an experiment I conducted at a sound field using TY-89. The results of this experiment suggest that the frequency spectrum intelligibility of noise as well as time-dependent changes in the sound pressure level of the noise exert an influence on communication disruption in patients with sensorineural hearing loss.