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This study investigated the relation between annoyance and single-number quantities to rate heavy-weight floor impact sound insulation. Laboratory experiments were conducted to evaluate the subjective response of annoyance resulting from heavy-weight floor impact sounds recorded in wooden houses. Stimuli had two typical spectra and their modified versions, which simulate the precise change in frequency response resulting from insulation treatments. Results of the first experiment showed that the Zwicker's percentile loudness (N(5)) was the quantity to rate most well annoyance of heavy-weight impact sound over a wide sound level range. The second experiment revealed that arithmetic average (L(iFavg,Fmax)) of octave-band sound pressure levels measured using the time constant "fast" and Zwicker's percentile loudness (N(5)) much better described annoyance by the precise change in the sound spectrum attributable to insulation treatments than Japanese standardized single-number quantities (L(i,Fmax,r), L(iA,Fmax), and L(i,Fmax,Aw)) do. Japanese standardized single-number quantities using the A-weighting curve as a rating curve were found to be excessively influenced by the 63 Hz octave-band sound level and have the great sound level-dependences in the relation with subjective ratings.

Hearing thresholds for pure tones from 2 kHz to 28 kHz were measured. A 2AFC procedure combined with a 3-down 1-up transformed up-down method was employed to obtain threshold values that were less affected by listener's criterion of judgment. From some listeners, threshold values of 88 dB SPL or higher were obtained for a tone at 24 kHz, whereas thresholds could not be obtained from all participants at 26 kHz and above. Furthermore, thresholds were also measured under masking by a noise low-pass filtered at 20 kHz. At frequencies above 20 kHz, the difference of threshold values between with and without the masking noise was a few decibels, indicating that the tone detection was not affected by subharmonic components that might have appeared in the lower frequency regions. The results of measurement also showed that the threshold increased rather gradually for tones from 20 to 24 kHz whereas it increased sharply from 14 to 20 kHz.

The statistical distribution of normal hearing thresholds for pure tones of frontal incidence under binaural, free-field listening conditions was estimated as a function of frequency. First, the form of threshold distribution was investigated with threshold measurement data of the present study and those of other studies. Analytical results indicate that the threshold distribution has a form of normal distribution for the frequency range from 25 Hz to 16 kHz. Second, under the assumption of normality, standard deviations of thresholds were calculated for the frequency range from 25 Hz to 18 kHz by combining available threshold data of different studies. A supplementary experiment showed that thresholds at frequencies above 16 kHz were measurable with high reliability. These results illustrate the profile of our auditory sensitivity more accurately because they account for individual differences.

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